Suomi NPP (National Polar-orbiting Partnership) Mission
NPP is a joint NASA/IPO (Integrated Program Office)/NOAA LEO weather satellite mission initiated in 1998. The primary mission objectives are:
1) To demonstrate the performance of four advanced sensors (risk reduction mission for key parts of the NPOESS mission) and their associated Environmental Data Records (EDR), such as sea surface temperature retrieval.
2) To provide data continuity for key data series observations initiated by NASA's EOS series missions (Terra, Aqua and Aura) - and prior to the launch of the first NPOESS series spacecraft. Because of this second role, NPP is sometimes referred to as the EOS-NPOESS bridging mission.
Three of the mission instruments on NPP are VIIRS (Visible/Infrared Imager and Radiometer Suite), CrIS (Cross-Track Infrared Sounder), and OMPS (Ozone Mapping and Profiler Suite). These are under development by the IPO. NASA/GSFC developed a fourth sensor, namely ATMS (Advanced Technology Microwave Sounder). This suite of sensors is able to provide cloud, land and ocean imagery, covering the spectral range from the visible to the thermal infrared, as well as temperature and humidity profiles of the atmosphere, including ozone distributions. In addition, NASA is developing the NPP S/C and providing the launch vehicle (Delta-2 class). IPO is providing satellite operations and data processing for the operational community; NASA is supplying additional ground processing to support the needs of the Earth science community. 3) 4) 5) 6) 7) 8)
CERES instrument selected for NPP and NPOESS-C1 missions: 9)
In early 2008, the tri-agency (DOC, DoD, and NASA) decision gave the approval to add the CERES (Clouds and the Earth's Radiant Energy System) instrument of NASA/LaRC to the NPP payload. The overall objective of CERES is to provide continuity of the top-of-the-atmosphere radiant energy measurements - involving in particular the role of clouds in Earth's energy budget. Clouds play a significant, but still not completely understood, role in the Earth's radiation budget. Low, thick clouds can reflect the sun's energy back into space before solar radiation reaches the surface, while high clouds trap the radiation emitted by the Earth from escaping into space. The total effect of high and low clouds determines the amount of greenhouse warming. - CERES products include both solar-reflected and Earth-emitted radiation from the top of the atmosphere to the Earth's surface.
In addition, the tri-agency decision called also for adding two instruments, namely CERES and TSIS (Total Solar Irradiance Sensor), to the payload of the NPOESS-C1 mission.
Background: The CERES instrument is of ERBE (Earth Radiation Budget Experiment) heritage of NASA/LaRC, first flown on the ERBS (Earth Radiation Budget Satellite) mission, launch Oct. 5, 1984, then on NOAA-9 (launch Dec. 12, 1984), and NOAA-10 (launch Sept. 17, 1986). The CERES instrument is flown on TRMM (Tropical Rainfall Measuring Mission), launch Nov. 27, 1997, as a single cross-track radiance sensor of short (0.3-5 μm), long- (8-12 μm) and total wave (0.3-100 μm; prototype flight model flown on TRMM). Two further advanced CERES instrument assemblies are also being flown on NASA's Terra mission (launch Dec. 18, 1999) as a dual-track scanner (two radiometers) in XT (Cross-Track ) support or in a RAPS (Rotational Azimuth Plane Scan) support mode. Another CERES instrument system (two radiometers) are being flown on Aqua of NASA (launch May 4, 2002).
The CERES instrument on NPP will provide continuity the long climate data record of the Earth's radiant energy.
Table 2: JPSS (Joint Polar Satellite System) - NPOESS program terminated 10)
Figure 1: Overview of Suomi NPP mission segments and architecture (image credit: NASA) 11)
Figure 2: NOAA POES continuity of weather observations (image credit: NOAA)
The Suomi NPP spacecraft has been built and integrated by BATC (Ball Aerospace and Technologies Corporation) of Boulder, CO (NASA/GSFC contract award in May 2002). The platform design is a variation of BATC's BCP 2000 (Ball Commercial Platform) bus of ICESat and CloudSat heritage. The spacecraft consists of an aluminum honeycomb structure. 12) 13) 14)
The ADCS (Attitude Determination and Control Subsystem) provides 3-axis stabilization using 4 reaction wheels for fine attitude control, 3 torquer bars for momentum unloading, thrusters for coarse attitude control (such as during large-angle slews for orbital maintenance), 2 star trackers for fine attitude determination, 3 gyros for attitude and attitude rate determination between star tracker updates, 2 Earth sensors for safe-mode attitude control, and coarse sun sensors for initial attitude acquisition, all monitored and controlled by the spacecraft controls computer. ADCS provides real-time attitude knowledge of 10 arcsec (1 sigma) at the S/C navigation reference base, real-time spacecraft position knowledge of 25 m (1 sigma), and attitude control of 36 arcsec (1 sigma).
The EPS (Electrical Power Subsystem) uses GaAs solar cells to generate an average power of about 2 kW (EOL). The solar array rotates once per orbit to maintain a nominally normal orientation to the sun). In addition, a single-wing solar array is mounted on the anti-solar side of the S/C; its function is to preclude thermal input into the sensitive cryo radiators of the VIIRS and CrIS instruments. A regulated 28 ±6 VDC power bus distributes energy to all S/C subsystems and instruments. A NiH (Nickel Hydrogen) battery system provides power for eclipse phase operations.
Figure 3: Artist's rendition of the deployed Suomi NPP spacecraft (image credit: BATC)
The C&DHS (Command & Data Handling Subsystem) collects instrument data (12 Mbit/s max total) via an IEEE 1394a-2000 "FireWire" interface (VIIRS, CrIS and OMPS instruments), and stores the data on board. Communications with ATMS occurs across the MIL-STD-1553 data bus. A new 1394/FireWire chipset was developed for the communication support, bringing spaceborne communications (onboard data handling and RF data transmission) onto a new level of service range and performance.
Upon ground command or autonomously, the C&DHS transmits stored instrument data to the communication system for transmission to the ground. Also, the C&DHS generates a real-time 15 Mbit/s data stream consisting of instrument science and telemetry data for direct broadcast via X-band to in-situ ground stations.
Table 3: Some NPP spacecraft characteristics
The spacecraft is designed to be highly autonomous. For satellite safety, the S/C controls computer monitors spacecraft subsystem and instrument health. It can take action to protect itself (for example, in the event of an anomaly that threatens the thermal or optical safety and health of the S/C, then it can enter into a safe or survival mode and stay in the mode indefinitely until ground analysis and resolution of the anomaly). In addition, the satellite is designed to require infrequent uploads of commands (the instruments operate mainly in a mapping mode and therefore require few commands even for periodic calibration activities, and a sufficiently large command buffer is available for storage of approximately 16 days of commands).
The spacecraft has an on-orbit design lifetime of 5 years (available consumables for 7 years). The S/C dry mass is about 1400 kg. NPP is designed to support controlled reentry at the end of its mission life (via propulsive maneuvers to lower the orbit perigee to approximately 50 km and target any surviving debris for open ocean entry). NPP is expected to have sufficient debris that survives reentry so as to require controlled reentry to place the debris in a pre-determined location in the ocean.
Figure 4: Photo of the nadir deck of the NPP spacecraft (image credit: BATC, IPO)
Figure 5: Suomi NPP spacecraft on-orbit configuration (image credit: NASA)
Launch: The NPP spacecraft was launched on October 28, 2011 on a Delta-2-7920-10 vehicle from VAFB, CA (launch provider: ULA). The launch delay of nearly a year was due to development/testing problems of the CrIS (Cross-track Infrared Sounder) instrument. 15) 16) 17)
Orbit: Sun-synchronous near-circular polar orbit (of the primary NPP), altitude = 824 km, inclination =98.74º, period = 101 minutes, LTDN (Local Time on Descending Node) at 10:30 hours. The repeat cycle is 16 days (quasi 8-day).
Figure 6: Photo of the NPP launch (image credit: NASA)
Secondary payloads: The secondary payloads on the Suomi NPP mission are part of NASA's ElaNa-3 (Educational Launch of Nanosatellites) initiative. All secondary payloads will be deployed from standard P-PODs (Poly Picosatellite Orbital Deployer). 18)
• AubieSat-1, a 1 U CubeSat of AUSSP (Auburn University Student Space Program), Auburn, AL, USA.
• DICE (Dynamic Ionosphere CubeSat Experiment), two nanosatellites (1.5U CubeSats) of the DICE consortium (Utah State University, Logan, UT, USA) with a total mass of 4 kg.
• E1P-2 (Explorer-1 PRIME-2) flight unit-2, a CubeSat mission of MSU (Montana State University), Bozeman, MT, USA.
• RAX-2 (Radio Aurora eXplorer-2), an NSF-sponsored 3U CubeSat of the University of Michigan, Ann Arbor, MI, USA
• M-Cubed (Michigan Multipurpose Minisat), a 1U CubeSat of the University of Michigan, Ann Arbor, MI. M-Cubed features also the collaborative JPL payload called COVE (CubeSat On-board processing Validation Experiment).
Orbit of the secondary payloads: After the deployment of the NPP primary mission, the launch vehicle transfers all secondary payloads into an elliptical orbit for subsequent deployment. This is to meet the CubeSat standard of a 25 year de-orbit lifetime as well as the science requirements of the payloads riding on this rocket. The rocket will take care of the maneuvering and when it reaches the correct orbit, it will deploy all of the secondary payloads, into an orbit of ~ 830 km x ~ 350 km, inclination = 99º.
The NPP satellite collects instrument data, stores the data onto a solid-state recorder of about 280 Gbit capacity. A two-axis gimbaled X-band antenna is mounted on a post above the payload to provide a high bandwidth downlink. Source science data are generated at a rate of about 12.5 Mbit/s. Global, or stored mission data will be downlinked at X-band frequencies (8212.5 MHz, data rate of 300 Mbit/s) to a 13 m ground receiving station located at Svalbard, Norway.
Two wideband transmissions carry NPP mission data: SMD (Stored Mission Data) and HRD (High-Rate Data). These transmissions are distinct from the narrowband data streams containing the satellite's housekeeping telemetry. Mission data are collected from each of the five instruments (ATMS, VIIRS, CrIS, OMPS, CERES).
These data, along with spacecraft housekeeping data, are merged and provided to the ground on a real-time 15 Mbit/s downlink, called HRD direct broadcast. Instrument and housekeeping data are also provided to the SSR (Solid State Recorder) for onboard storage and playback as SMD. The SMD are stored in the spacecraft's SSR and downlinked at 300 Mbit/ss through playback of the SSR once per orbit over the NPP/NPOESS SvalSat ground station in Svalbard, Norway.
The HRD stream is similar to the SMD as it consists of instrument science, calibration and engineering data, but it does not contain data from instrument diagnostic activities. The HRD is constantly transmitted in real time by the spacecraft to distributed direct broadcast users. Output to the HRD transmitter is at a constant 15 Mbit/s rate.
Data acquisition: In early 2004, IPO in cooperation with NSC (Norwegian Space Center), installed a 13 m antenna dish - a dual X/S-band configuration, at SGS (Svalbard Ground Station), located at 78.216º N, 20º E on the Norwegian Svalbard archipelago (also referred to as Spitzbergen) near the town of Longyearbyen. The SGS complex is owned by the Norwegian Space Center (Norsk Romsenter), Oslo, Norway, and operated by the Tromsø Satellite Station (TSS) through its contractor KSAT (Kongsberg Satellite Services). SGS is the primary data downlink site for global stored mission data (SMD) from NPP. Svalbard is located at a high enough latitude to be able to "see" (i.e., track) all 14 daily NPP satellite passes. 19)
The global NPP data will be transmitted from Svalbard within minutes to the USA via a fiber-optic cable system that was completed in January 2004 as a joint venture between the IPO, NASA, and NSC. Once the data stream is in the USA, the RDRs (Raw Data Records) will be processed into SDRs (Sensor Data Records) and EDRs by the Interface Data Processing Segment (IDPS). The performance goal calls for EDR delivery within 3 hours of acquisition. - NPP also focuses on ground segment risk reduction by providing and testing a subset of an NPOESS-like ground segment. Developed algorithms can be thoroughly tested and evaluated. This applies also to the methods of instrument verification, calibration, and validation.
Note: The new antenna and fiber-optic link at SGS are already being used to acquire data of five to ten Coriolis/WindSat passes/day and delivery of the data to users in a reliable and timely manner. Subsequent to the NPP mission, the Svalbard site and the high-speed fiber-optic link will also serve as one node in a distributed ground data communications system for NPOESS acquisition service.
The TT&C function uses S-band communications with uplink data rates of up to 32 kbit/s and downlink rates of up to 128 kbit/s. The NOAA network of polar ground stations will be used for mission operations (back-up TT&C services via TDRSS through S-band omni antennas on the satellite).
Figure 7: Overview of Suomi NPP spacecraft communications with the ground segment (image credit: NASA) 20)
Suomi NPP broadcast services:
In addition, NPP will have a real-time HRD (High Rate Data) downlink in X-band (7812.0 MHz ± 0.03 MHz) direct broadcast mode to users equipped with appropriate field terminals. The objectives are to validate the innovative operations concepts and data processing schemes for NPOESS services. NPP world-wide users will already experience NPOESS-like data well in advance of the first NPOESS flight in 2013. The NPP broadcast services to the global user community are: 21) 22) 23) 24)
• X-band downlink at 30 Mbit/s
• Convolutional coding
• QPSK (Quadra-Phase Shift Keying) modulation
• An X-band acquisition system of 2.4 m diameter aperture is sufficient for all data reception. NASA will provide:
• Real-Time Software Telemetry Processing System
• Ground-Based Attitude Determination module
• Stand-alone Instrument Level-1 and select Level-2 (EDR) algorithms
• Instrument-specific Level 1 (SDR) & select Level-2 (EDR) visualization & data formatting tools
Figure 8: The field terminal architecture of the NPP / NPOESS satellites (image credit: NASA, NOAA, IPO)
The DRL (Direct Readout Laboratory) of NASA/GSFC is committed to promote continuity and compatibility among evolving EOS direct broadcast satellite downlink configurations and direct readout acquisition and processing systems. The DRL bridges the EOS missions with the global direct readout community by establishing a clear path and foundation for the continued use of NASA's Earth science DB data. The DRL is also involved in continued efforts to ensure smooth transitions of the Direct Broadcast infrastructure from the EOS mission to the next generation NPP (NPOESS Preparatory Project) and NPOESS (National Polar-orbiting Operational Environmental Satellite System) missions in the future. In an effort to foster global data exchange and to promote scientific collaboration, the DRL with support from other groups, is providing the user community access to Earth remote sensing data technologies and tools that enable the DB community to receive, process, and analyze direct readout data.
DRL developed IPOPP (International Polar Orbiter Processing Package), the primary processing package that will enable the Direct Readout community to process, visualize, and evaluate NPP and NPOESS sensor and EDRs (Environmental Data Records), which is a necessity for the Direct Readout community during the transition from the Earth Observing System (EOS) era to the NPOESS era. DRL developed also the NISGS (NPP In-Situ Ground System). The IPOPP will be: 25)
• Freely available
• Portable to Linux x86 platforms
• Efficient to run on modest hardware
• Simple to install and easy to use
• Able to ingest and process Direct Broadcast overpasses of arbitrary size
• Able to produce core and regional value-added EDR products.
Table 4: NPP & NPOESS Direct Readout link characteristics
• September 25, 2017: Hurricane Maria was analyzed in visible and infrared light as NASA-NOAA's Suomi NPP passed overhead over two days. NASA's GPM satellite also provided a look at Maria's rainfall rates. 26)
- On Sept. 23 at 8:12 a.m. EDT (12:12 UTC) the GPM (Global Precipitation Measurement) mission core observatory estimated of hourly rainfall in multiple intense rainfall bands of thunderstorms around Maria's western side. Rain was found falling at a rate of over 137 mm/hour and some thunderstorm tops in these rain bands were found to reach heights above 15.7 km. GPM is managed by NASA and JAXA (Japan Aerospace Exploration Agency).
Figure 9: The GPM core observatory estimated of hourly rainfall of Hurricane Maria. Rain was found falling at a rate of over 137 mm/hour (image credit: NASA/JAXA, Hal Pierce)
- On Sept. 24 at 1:54 p.m. EDT (17:54 UTC), the VIIRS (Visible Infrared Imaging Radiometer Suite) instrument aboard NASA-NOAA's Suomi NPP satellite captured a visible light image of Hurricane Maria that showed the eye had become cloud filled. Maria was located northeast of Bahamas and far off the Florida east coast (Figure 10).
Figure 10: The VIIRS instrument provided this image of Hurricane Maria when it was northeast of Bahamas and east of the Florida east coast (image credit: NOAA/NASA Goddard Rapid Response Team)
- On Sept. 25 at 2:12 a.m. EDT (06:12 UTC) the VIIRS instrument aboard NASA-NOAA's Suomi NPP satellite provided tan infrared image of Hurricane Maria (Figure 11). The infrared image provided forecasters with temperature data that showed where the strongest storms were located within the hurricane. Coldest clouds tops and strongest storms were in the southeastern quadrant where temperatures were as cold as or colder than minus minus 62.2º C. NASA research has shown that storms with cloud top temperatures that cold can produce heavy rainfall.
Figure 11: The VIIRS instrument aboard NASA-NOAA's Suomi NPP satellite provided this infrared image of Hurricane Maria. Coldest cloud tops (red) and strongest storms were in the southeastern quadrant (image credit: NOAA/NASA Goddard Rapid Response Team)
• September 9, 2017: Meteorologists struggled to find the right words to describe the situation as a line of three hurricanes—two of them major and all of them threatening land—brewed in the Atlantic basin in September 2017. 27)
- Forecasters were most concerned about Irma, which was on track to make landfall in densely populated South Florida on September 10 as a large category 4 storm. Meanwhile, category 2 Hurricane Katia was headed for Mexico, where it was expected to make landfall on September 9. And just days after Irma devastated the Leeward Islands, the chain of small Caribbean islands braced for another blow—this time from category 4 Hurricane Jose.
- The VIIRS instrument on the Suomi NPP satellite captured the data for a mosaic of Katia, Irma, and Jose as they appeared in the early hours of September 8, 2017. The images were acquired by the VIIRS "day-night band," which detects light signals in a range of wavelengths from green to near-infrared, and uses filtering techniques to observe signals such as city lights, auroras, wildfires, and reflected moonlight. In this case, the clouds were lit by the nearly full Moon. The image is a composite, showing cloud imagery combined with data on city lights.
Figure 12: Suomi NPP image of Hurricanes Katia, Irma and Jose, captured on September 8, 2017 (image credit: NASA Earth Observatory,images by Joshua Stevens and Jesse Allen, using VIIRS day-night band data from the Suomi NPP, story by Adam Voiland)
Figure 13: MODIS on NASA's Terra satellite acquired a natural-color image of Irma at 16:00 UTC on September 8, 2017 (image credit: NASA Earth Observatory,images by Joshua Stevens and Jesse Allen, using MODIS data from LANCE (Land Atmosphere Near real-time Capability for EOS), story by Adam Voiland)
• On September 6, 2017, Hurricane Irma slammed into the Leeward Islands on its way toward Puerto Rico, Cuba, and the U.S. mainland. As the category 5 storm approaches the Bahamas and Florida in the coming days, it will be passing over waters that are warmer than 30 degrees Celsius (86 degrees Fahrenheit)—hot enough to sustain a category 5 storm. Warm oceans, along with low wind shear, are two key ingredients that fuel and sustain hurricanes. 28)
- The map of Figure 14 shows sea surface temperatures in the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico on September 5, 2017. The data were compiled by NOAA's CRWP (Coral Reef Watch Program), which blends observations from the Suomi NPP, MTSAT, Meteosat, and GOES satellites and computer models. The mid-point of the color scale is 27.8°C, a threshold that scientists generally believe to be warm enough to fuel a hurricane. The yellow-to-red line on the map represents Irma's track from September 3–6.
- By definition, category 5 storms deliver maximum sustained winds of at least 252 km/ hour. When it hit the Leeward Islands, Irma's winds surpassed 295 km/ hour, making it the strongest storm to ever hit the islands and one of the strongest storms ever measured in the Atlantic basin.
Figure 14: Sea surface temperatures in the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico on September 5, 2017. NOAA compiled the data from the Suomi NPP, MTSAT, Meteosat, and GOES satellites and computer models (image credit: NOAA, NASA Earth Observatory image by Joshua Stevens and Jesse Allen)
• September 6, 2017: With dozens of wildfires burning across the western United States and Canada, many North Americans have had the acrid taste of smoke in their mouths during the past few weeks. On September 5, 2017, the NIFC (National Interagency Fire Center) reported more than 80 large fires burning in nine western U.S. states. People living in large stretches of northern California, Oregon, Washington, and Idaho have been breathing what the U.S. government's Air Now website rated as "hazardous" air. 29)
- The natural-color mosaic of Figure 15 was made from several scenes acquired on September 4, 2017, by the VIIRS (Visible Infrared Imaging Radiometer Suite) on the Suomi National Polar-orbiting Partnership (Suomi-NPP) satellite. The OMPS (Ozone Mapper Profiler Suite ) on Suomi NPP also collected data on airborne aerosols as they were swept by winds from west to east across the continental United States (second image).
- The OMPS map depicts relative aerosol concentrations, with lower concentrations appearing in yellow and higher concentrations appearing in dark orange-brown. Note that the sensor detects aerosols in high-altitude plumes more readily than lower plumes, so this map does not reflect air quality conditions at "nose height." Rather it shows where large plumes of smoke were lofted several kilometers up into the atmosphere.
- On September 5, roughly 7.8 million acres had burned in the United States since the beginning of 2017, according to NIFC. "While it is unlikely that this season will be record-breaking for modern fire record keeping in the western United States, it is above normal relative to the last decade—which has seen abundant fire activity," said John Abatzoglou, a fire researcher at the University of Idaho. Unusually warm and dry conditions across a broad swath of the West has fueled the active fire season, noted Abatzoglou. A wet winter in some parts of the West also contributed by triggering the growth of more grass in the spring—grass that turns into fuel for fires in the summer.
Figure 15: VIIRS natural color image, acquired on Sept. 4, 2017 (image credit: NASA Earth Observatory, images by Joshua Stevens and Jesse Allen, using Suomi NPP VIIRS data, Story by Adam Voiland)
Figure 16: The OMPS map depicts relative aerosol concentrations, with lower concentrations appearing in yellow and higher concentrations appearing in dark orange-brown (image credit: NASA Earth Observatory, images by Joshua Stevens and Jesse Allen, using Suomi NPP OMPS data provided courtesy of Colin Seftor (SSAI), Story by Adam Voiland)
• September 3, 2017: Hurricane Harvey changed the landscape of southern Texas and the lives of millions of people. The storm also changed the surface profile of the Gulf of Mexico, though those effects are likely to be short-lived. 30)
- When Harvey crossed the Yucatán Peninsula into the Gulf of Mexico on August 22–23, 2017, the tropical depression moved into waters that were 1.5 to 4º Celsius warmer than the long-term regional average for sea surface temperatures. Hurricanes feed off of warm ocean temperatures, like a fire relies on a steady oxygen supply to keep burning. "So this deep, warm pool of water helped provide additional fuel for Harvey to intensify," said Dalia Kirschbaum, a scientist and natural hazards specialist at NASA/GSFC (Goddard Space Flight Center).
- Once in the Gulf, Harvey grew rapidly and sped toward the Texas coast as a category 4 hurricane — then lingered for five days as a potent tropical storm. In the process, the storm dropped unprecedented amounts of rainwater on Houston and southern Texas while churning up the Gulf of Mexico.
- The maps of Figure 17 show sea surface temperatures in the western Gulf of Mexico on August 23 and August 30, 2017, as well as the storm track for Harvey. The pair of maps of Figure 18 show sea surface temperature anomalies; that is, how much the surface layer was above or below the long-term average temperature for this time of year. The data for all of the maps were compiled by Coral Reef Watch, which blends observations from the Suomi NPP, MTSAT, Meteosat, and GOES satellites with computer models.
- All of the fresh rainwater and the ocean mixing from the storm combined to dramatically alter the surface waters of the Gulf. Cooling naturally as it rose through the atmosphere, the water that fell back onto the sea as rain likely would have been cooler than the surface waters. At the same time, the winds and waves of the storm worked to disperse warm surface water and to bring up cooler water from the ocean depths.
- In theory, the cooler water now near the surface of the northern Gulf of Mexico should make it less likely for a new storm to develop or intensify there in the coming weeks. However, the waters of the Gulf are not exactly cool. Scientists generally agree that SSTs (Sea Surface Temperatures) should be above 27.8°C to promote the development and intensification of hurricanes. (There are some exceptions.) So even some of the light blues on our sea surface temperature maps are still warm enough for storms.
Figure 17: Surface temperatures in the Golf western Gulf of Mexico, acquired on August 23 and August 30, 2017, as well as the storm track for Harvey. The data were compiled by Coral Reef Watch, which blends observations from the Suomi NPP, MTSAT, Meteosat, and GOES satellites with computer models (image credit: NASA Earth Observatory, images by Joshua Stevens, using data from Coral Reef Watch and Unisys, Story by Mike Carlowicz)
Figure 18: Western Golf of Mexico sea surface temperature anomalies - difference from the long-term average temperature for this time of the year. The observations were in the time frame August 23 and August 30, 2017. The data were compiled by Coral Reef Watch, which blends observations from the Suomi NPP, MTSAT, Meteosat, and GOES satellites with computer models (image credit: NASA Earth Observatory, images by Joshua Stevens, using data from Coral Reef Watch and Unisys, Story by Mike Carlowicz)
Table 5: Overview of the VIIRS data product performance - continuing with the JPSS (Joint Polar Satellite System) missions 31)
• On June 17,2017, lightning reportedly ignited a deadly wildfire that spread across the mountainous areas of Pedrógão Grande—a municipality in central Portugal located about 160 km northeast of Lisbon. The MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA's Terra satellite captured a daytime image of smoke billowing northward from areas of active burning on June 18. The following night the blaze continued to burn so bright that it was visible from space. 32)
- VIIRS (Visible Infrared Imaging Radiometer Suite) on the Suomi NPP satellite captured a nighttime image of the fire at 2:48 a.m. local time (01:48 UTC on June 19, 2017, Figure 19). For comparison, the second image of Figure 20 shows the same area in the predawn hours of June 16. Turn on the image-comparison tool to see the fires brighten the rural landscape between the urban areas. Note that some differences in brightness and sharpness are due to the presence of more cloud cover in the June 19 image. The fire was imaged by a special "day-night band" that detects light in a range of wavelengths from green to near-infrared and uses light intensification to detect dim signals.
- Fires across Portugal's forested landscape during the warm, dry summer months are not uncommon. In 2016, hundreds of fires raged on the mainland and also on the Portuguese island of Madeira. The high death toll associated with this week's fire, however, led The New York Times and other media to report it as "Portugal's worst forest fire in more than half a century."
Figure 19: VIIRS nighttime image of the fires in Portugal acquired on June 19, 2017 (image credit: NASA Earth Observatory, image by Jesse Allen, using VIIRS day-night band data from the Suomi NPP, story by Kathryn Hansen)
Figure 20: VIIRS image of the same region in Portugal acquired in the predawn hours on June 16, 2017 (image credit: NASA Earth Observatory, image by Jesse Allen, using VIIRS day-night band data from the Suomi NPP, story by Kathryn Hansen)
• May 16, 2017: Image comparison: Unlike most satellite imagery and data, views of Earth at night tell a distinctly human story. From fires to fishing boats to urban neon, lights show where people have made their homes, set up their industries, and laid down their roads. The lack of light usually reflects rural or uninhabited areas, though sometimes it means there is not enough electricity to keep lights on through the night. 33)
- Changing patterns of light over time also tell us something. The images above show differences in nighttime lighting between 2012 and 2016 in Syria and Iraq, among several Middle Eastern countries. Such images interest demographers, engineers, and social scientists because they can indicate economic development or the lack of it. Some changes reflect increases or decreases in electric power generation or in the steadiness of the supply. Even areas that switch to LEDs or other energy efficient lights can show up over time.
- Night light images also have value for international relief and humanitarian organizations, which can use this data to pinpoint areas in need. NASA makes its Earth observations freely and openly available (often via the Web) to those seeking solutions to important global issues. Several current applied sciences efforts within NASA are aimed at making satellite data more readily accessible for disaster response and the delivery of aid.
- Each image of Figures 21 and 22 is drawn from a global composite that was made by selecting the best cloud-free nights in each month over each land mass on Earth. The data come from the VIIRS (Visible Infrared Imaging Radiometer Suite) on the NASA-NOAA Suomi NPP satellite. VIIRS includes a special "day/night band," a low-light sensor that makes quantitative measurements of light emissions and reflections, allowing researchers to distinguish the intensity, types, and sources of night lights and to observe how they change over several years.
- A research team led by Miguel Román of NASA's Goddard Space Flight Center recently released new global maps of Earth at night from 2012 and 2016. Román and colleagues are collaborating with institutions such as the U.S. Federal Emergency Management Agency and the United Nations to enable near-real-time applications of such data, in addition to fundamental research.
- In the images of Figures 21 and 22, the changes are most dramatic around Aleppo, but also extend through western Syria to Damascus. Over the four years, lighting increased in areas north of the Syrian border in Turkey and to the west in Lebanon. According to a 2015 report from the Voice of America, as much as 80 percent of the lights have gone out in Syria over the past few years.
Figure 21: VIIRS image on Suomi NPP of the Syria and Irak region acquired in 2012 (image credit: NASA Earth Observatory, images by Joshua Stevens, story by Michael Carlowicz)
- In Iraq, some northern sections near Mosul saw a decrease in light over the years, while areas around Baghdad, Irbil, and Kirkuk saw increases. Note, too, the change in electric light patterns along the Tigris and Euphrates river basins.
- International agencies such as the United Nations Institute for Training and Research Operational Satellite Applications Program (UNITAR-UNOSAT) have used such imagery in the past few years "to track fast-moving conflicts and to update our UN colleagues on where the front lines might be," said Lars Bromley, a remote sensing specialist with the agency. UNOSAT works to "improve the integration of satellite imagery and geospatial data in supporting global UN operations and activities in the areas of disaster response, humanitarian support, human security, and human rights." Nighttime imagery helps relief and peacekeeping groups identify areas that are most in need of aid and support.
Figure 22: VIIRS image on Suomi NPP of the Syria and Irak region acquired in 2016 (image credit: NASA Earth Observatory, images by Joshua Stevens, story by Michael Carlowicz)
• April 12, 2017: NASA scientists are releasing new global maps of Earth at night, providing the clearest yet composite view of the patterns of human settlement across our planet. This composite image, one of three new full-hemisphere views, provides a view of the Americas at night. The clouds and sun glint — added here for aesthetic effect — are derived from MODIS instrument land surface and cloud cover products. 34)
- In the years since the 2011 launch of the NASA-NOAA Suomi- NPP (National Polar-orbiting Partnership) satellite, a research team led by Earth scientist Miguel Román of NASA/GSFC (Goddard Space Flight Center) has been analyzing night lights data and developing new software and algorithms to make night lights imagery clearer, more accurate and readily available. They are now on the verge of providing daily, high-definition views of Earth at night, and are targeting the release of such data to the science community later this year.
- Today they are releasing a new global composite map of night lights as observed in 2016, as well as a revised version of the 2012 map. The NASA group has examined the different ways that light is radiated, scattered and reflected by land, atmospheric and ocean surfaces. The principal challenge in nighttime satellite imaging is accounting for the phases of the moon, which constantly varies the amount of light shining on Earth, though in predictable ways. Likewise, seasonal vegetation, clouds, aerosols, snow and ice cover, and even faint atmospheric emissions (such as airglow and auroras) change the way light is observed in different parts of the world.
Figure 23: Earth at Night map (image credit: NASA Earth Observatory images by Joshua Stevens, using Suomi NPP VIIRS data from Miguel Román, NAS/GSFC) 35)
Suomi NPP observes nearly every location on Earth at roughly 13:30 and at 1:30 hrs (local time) each day, observing the planet in vertical 3000 km strips from pole to pole. VIIRS includes a special "day-night band," a low-light sensor that can distinguish night lights with six times better spatial resolution and 250 times better resolution of lighting levels (dynamic range) than previous night-observing satellites. And because Suomi NPP is a civilian science satellite, the data are freely available to scientists within minutes to hours of acquisition.
Figure 24: Composite image of Mid-Atlantic and Northeastern U.S. (Boston-Washington corridor) at night, 2016 (image credit: NASA Earth Observatory images by Joshua Stevens, using Suomi NPP VIIRS data from Miguel Román, NASA/GSFC)
• February 22, 2017: Yet another series of atmospheric rivers has drenched California and the American West in a stunning turnaround from five years of drought. Many parts of California have received nearly twice as much rain as normally falls in the first five months of a water year, which began on October 1. 36)
- Flood and landslide warnings are in effect in many counties, particularly in the Sacramento Valley, which is crossed by several rivers and sits downstream from several large reservoirs and dams. According to news reports, more than two dozen mud/debris flows have been reported across California, and at least 30 major roads have been flooded at various times in the past week. Spillways have been opened at the Anderson, Oroville, and Monticello dams, among others.
- The map of Figure 26 shows satellite-based measurements of rain, snow, and other wintry precipitation as it has accumulated over California, Nevada, Utah, and Arizona this year. Specifically, it adds the daily precipitation totals from December 31, 2016, to the evening of February 20, 2017. These are remotely-sensed estimates, and local amounts can be significantly higher when measured from the ground. The brightest areas on the map depict as much as 1000 mm of precipitation.
- More than 12 cm of rain fell in parts of northern California and along the western foothills of the Sierra Nevada on February 19–20. Daily rainfall records for February 20 were doubled in San Jose (4.75 cm) and San Francisco (5.5 cm ). According to Colorado State University meteorologist Phil Klotzbach and National Weather Service sources, San Francisco has received 41.6 cm of rain since January 1, while Oakland has received 52.85 cm; the typical yearly total is 58 cm.
- During an atmospheric river event in southern California on February 17–18, new rainfall records were set in Death Valley (1.65 cm) and Santa Barbara (10.6 cm). More than 100,000 people lost power in the Los Angeles Metropolitan area on February 17 due to the storms.
- Las Vegas Valley set a new record rainfall on February 18, measuring 1.1 cm that day. Locations on the west side of the valley received double that amount. Meanwhile, in northern Nevada, Mount Rose has been buried under 12.7 m of snow this winter. The Mount Rose Highway between Reno and Lake Tahoe has been closed by an avalanche that dropped 6 m of snow on the road.
Figure 25: VIIRS on Suomi NPP captured a natural-color image of conditions over the northeastern Pacific. Note the tight arc of clouds stretching from Hawaii to California, a visible manifestation of the atmospheric river pouring moisture into western states (image credit: NASA Earth Observatory, images by Jesse Allen and Joshua Stevens using VIIRS data)
Figure 26: Precipitation accumulated over the western states in 2017. The data come from IMERG (Integrated Multi-Satellite Retrievals for GPM), a product of the Global Precipitation Measurement mission (image credit: NASA Earth Observatory, images by Jesse Allen and Joshua Stevens using IMERG data of GPM)
• February 14, 2017: After extreme drought and water shortages plagued California for years, a series of winter storms pushed reservoirs in the Sacramento Valley to the brim in January and February 2017. Rivers and reservoirs are swollen throughout California. VIIRS on Suomi NPP captured the image of Figure 27 on Feb. 11, 2017. 37)
- For comparison, the image of Figure 28 shows the same area on November 9, 2016, before the wet weather arrived. Large amounts of water have pooled in the Yolo Bypass, a water storage area designed to minimize flooding in Sacramento. Sediment stirred up during the flooding has turned waterways throughout northern California—including San Pablo Bay and Suisun Bay—a dark shade of brown.
- With weather stations in the northern Sierra Nevada recording remarkably high levels of precipitation for the 2016-2017 water year, reservoir levels are well above the historical average in the Sacramento Valley and elsewhere in California. As of February 11, 2017, Lake Oroville stood at 151% of the historical average. Folsom Lake was at 144%, Lake Shasta was at 138%, Don Pedro Reservoir was at 141%, and Lake McClure was at 182%.
- At the Oroville Dam, the situation became dire on February 7, 2017, when a large hole appeared in the main concrete spillway, a part of the dam managers use to release excess water in a controlled fashion. The hole limited how much water authorities could safely release through the spillway, so water levels in the reservoir continued to rise. A few days later, water began flowing over an emergency spillway that has never before been used. When the emergency spillway began showing worrisome signs of erosion on February 12, authorities ordered the evacuation of 188,000 people living downstream.
- Lake Oroville's levels have declined since the evacuation order and the risk of a catastrophic failure has lessened. But reservoir managers remain concerned that rain showers forecast for this week could elevate reservoir water levels and stress the spillways again. As of 11 a.m. on February 13, the evacuation order remained in effect.
Figure 27: VIIRS on Suomi NPP captured this natural-color image of sediment-filled waterways in the Sacramento Valley on February 11, 2017 (image credit: NASA Earth Observatory, image by Jesse Allen, caption by Adam Voiland)
Figure 28: For comparison, VIIRS on Suomi NPP captured this natural-color image on Nov. 9, 2016, before the wet weather arrived (image credit: NASA Earth Observatory, image by Jesse Allen, caption by Adam Voiland)
• February 13, 2017: NASA has awarded the SNPPS (Suomi National Polar-Orbiting Partnership Sustainability) contract to BATC (Ball Aerospace and Technology Corp.) of Boulder, Colorado. This is an indefinite-delivery/indefinite quantity, cost-plus fixed-fee contract with the ability to issue task orders. Under this contract, Ball Aerospace will continue to provide sustaining engineering services to the JPSS (Joint Polar Satellite System) Flight Project and NOAA's Office of Satellite and Product Operations for the mission operations systems and subsystems, and deactivation of the Suomi NPP satellite. This effort will maintain the current operational phase of the satellite through the Suomi NPP mission life, including deactivation and contract closeout. 38)
- Suomi NPP provides continuity for NASA's EOS (Earth Observing System) and is a bridge between NOAA's legacy POES (Polar Orbiting Environmental Satellite) missions and the JPSS-1 (Joint Polar Satellite System-1) satellite, under development and integration at BATC. Its sensor complement has surpassed expectations for low noise and accuracy, and has provided useful data to forecasters beginning well before it gained operational status. The NWS (National Weather Service) uses Suomi NPP global measurements in its numerical weather prediction models. NPP's advanced imagery of clouds, ocean surface, land features and other physical parameters is key data for civilian and DoD forecasters. Suomi NPP's precise observations are improving the accuracy of global forecasts three to seven days in advance of significant weather events, including hurricanes and winter storms. 39)
• January 12, 2017: Starting from 14 :18 UTC on January 12, 2017, the Suomi NPP VIIRS Day/Night Band began to be produced operationally using the NOAA STAR (Satellite Applications and Research) Center delivered calibration parameters based on onboard and pitch maneuver data, which were previously delivered by external partners based on dark ocean special collect data. STAR has improved the calibration which will result in better radiometric quality especially for low radiances. With the new calibration, users should expect to see a significant reduction of erroneous negative radiances especially during new moon. 40)
• December 7, 2016: Many parts of eastern China were put on orange alert on December 4, 2016, when heavy smog veiled large swaths of the country. The haze stranded passengers at airports in northern China and slowed down city life in Beijing, which reached orange alert level on December 1. 41)
- An orange alert signals heavy pollution—a PM2.5 (particulate matter) density of more than 150 micrograms per cubic meter of air—for three consecutive days. Such high concentration of fine particles in the air can cause lung and heart problems for vulnerable individuals, including asthmatics, children, and the elderly.
- Low winter temperatures exasperate smog since they cause temperature inversions. Warm air settles atop a layer of cooler, denser, smog-ridden air, trapping it like a lid. High concentrations of smog frequently appear in cities like Beijing during winter.
Figure 29: VIIRS on the Suomi NPP satellite acquired this natural-color image of northeastern China on December 6. Photos taken from the ground also showed low visibility—less than 200 m, according to news reports. On December 5, People's Daily reported smog blanketing more than 60 Chinese cities (image credit: NASA Earth Observatory, image by Jeff Schmaltz)
• November 5, 2016: The Indian state of Punjab is known as India's breadbasket. Despite its relatively small size, Punjab ranks among the nation's top wheat and rice producers. For a few weeks in October and November, Punjab also becomes a major producer of air pollution. 42)
- Punjab has two growing seasons and two main crops. Rice is planted in May and grown through September; wheat is planted in November and grown through April. Since rice leaves behind a significant amount of plant debris after harvest, many farmers burn the leftover debris in October and November to quickly prepare their fields for the wheat crop.
- In early October 2016, Earth-observing satellites began to detect small fires in Punjab, and the number of fires increased rapidly in the following weeks. By November, thousands of fires burned across the state, and a thick pall of smoke hovered over India. VIIRS (Visible Infrared Imaging Radiometer Suite) on the Suomi NPP satellite captured a natural color image on November 2, 2016 (Figure 30). The map of Figure 31 shows the locations of the fires VIIRS also detected.
- Since the fires are small, short-lived, and burn at relatively low-temperatures, the smoke generally stays near the surface. On November 2, winds carried a stream of smoke — likely mixed with small particles of soil, dust, and partially burned plant material — toward New Delhi. The smoke from Punjab combined with urban pollution from vehicles, industry, and fireworks to push levels of particulate matter in the capital city to unusually high levels.
Figure 30: Thick smoke over northern India and Pakistan created by the fires of plant debris after the rice harvest. The image was acquired on Nov. 2, 2016 by the VIIRS instrument on Suomi NPP (image credit: NASA Earth Observatory, image by Joshua Stevens)
Figure 31: The fire locations detected by the thermal bands of VIIRS on Suomi NPP (image credit: NASA Earth Observatory, image by Joshua Stevens)
• October 28, 2016: After five years in space, the NOAA/NASA Suomi NPP mission continues to contribute significant advances in severe weather prediction and environmental monitoring leading to better forecasts and situational awareness for the nation and users worldwide. Suomi NPP is a bridge to NOAA's next generation JPSS (Joint Polar Satellite System) weather satellites. The JPSS-1 satellite is scheduled to launch in 2017 to complement the data from Suomi NPP. 43)
Currently NOAA's primary polar-orbiting weather satellite, Suomi NPP, provides critical input into weather forecasts beyond 48 hours and is increasing the consistency and accuracy of forecasts three to seven days in advance of a severe weather event for NOAA's National Weather Service. These data are also provided to other federal, state and local users; commercial weather sector; and international partners.
Research scientists throughout the United States and the world use Suomi NPP data as they study severe weather, atmospheric and oceanographic phenomena and climate. Data produced by Suomi NPP are derived from a new generation of instruments that will also fly on future JPSS satellites: Visible Infrared Imaging Radiometer Suite (VIIRS), Cross-track Infrared Sounder (CrIS), Advanced Technology Microwave Sounder (ATMS), and Ozone Mapping and Profiler Suite-Nadir (OMPS). Suomi NPP provides the first mission using these instruments, and also flies the fifth flight model of the Cloud and Earth Radiant Energy System (CERES).
Suomi NPP data are used to generate dozens of environmental data products, including measurements of atmosphere, oceans and land conditions. These include:
- Atmospheric temperature/moisture profiles
- Thunderstorms, tornado potential
- Ice detection
- Precipitation and floods
- Dense fog
- Volcanic ash
- Fire and smoke
- Sea surface temperature, ocean color
- Sea ice extent and snow cover /depth
- Polar satellite derived winds (speed/direction/height
- Vegetation greenness indices and health
- Oil spills.
It takes Suomi NPP 14 orbits to observe the entire Earth in one day. The weather and environmental mission data from its five instruments for each orbit are stored and transmitted to Earth every orbit.
Suomi NPP stored mission data is collected by a ground station in Svalbard, Norway, and is then routed to the NOAA Satellite Operations Facility in Suitland, Maryland, where it is processed and distributed. With JPSS-1, there will also be a transmission to antennas at McMurdo Station, Antarctica near the South Pole to enable data to be received and routed every half orbit, cutting the time processed data is sent to users by half. — In addition, Suomi NPP data are accessed by users through the use of direct broadcast antennas to quickly access Suomi NPP observations made while in view of each direct broadcast antenna to support critical missions (Ref. 43).
• In August 2016, tourists on a luxury cruise departed Seward Alaska and steered toward the waterways of the Canadian Arctic Archipelago. The excursion is one example of the growing human presence in an increasingly ice-free Northwest Passage — the famed high-latitude sea route that connects the northern Atlantic and Pacific oceans. In mid-August 2016, the southern route through the Passage was nearly ice-free. 44) 45)
- For most of the year, the Northwest Passage is frozen and impassible. But during the summer months, the ice melts and breaks up to varying degrees. The VIIRS (Visible Infrared Imaging Radiometer Suite) on the Suomi -NPP satellite captured the image of Figure 32 of the Northwest Passage on August 9, 2016. A path of open water can be traced along most of the distance from the Amundsen Gulf to Baffin Bay.
- "It was a warm winter and spring," said NASA sea ice scientist Walt Meier. That means that the seasonal ice—ice that grew since the end of last summer, and the type found throughout most of the Passage—is thinner than normal. Thinner ice can melt more easily, break up, and move out of the channels. A scattering of broken ice is visible just east of Victoria Island. "It looks pretty thin and disintegrating," Meier said. "I think an ice-strengthened ship could get through without too much trouble."
- The open water this year flows along the southern route, or "Amundsen route." It's not unusual for the southern route to open up to some degree, as it is more protected than the northern route and receives less sea ice directly from the Arctic Ocean.
Figure 32: The VIIRS instrument on Suomi NPP captured this image of the nearly ice-free Northwest Passage on August 9, 2016 (image credit: NASA Earth Observatory , Jeff Schmaltz)
• June 25, 2016: There's more than one way to feed a phytoplankton bloom in the Gulf of Alaska (Figure 33). Iron, a key nutrient for the growth of these tiny plant-like organisms, can enter the gulf waters from the air—via volcanic eruptions or airborne dust from dry lakebeds and streams. Other times, the nutrient stays closer to the ground, catching a ride to the gulf with the meltwater of thawing glaciers. 46)
- NASA scientists noted that this is the time of year when melt water from Alaska's glaciers flows through rivers and out into the Gulf of Alaska. The meltwater carries a supply of "rock flour," or "glacial flour"—the dusty remains of bedrock ground up by a glacier. Where it reaches the Gulf of Alaska, this rock flour imparts a milky turquoise color to the water.
- The rock flour also supplies the gulf with the iron, a nutrient that promotes phytoplankton growth by helping the organisms to process nitrate. Eddies such as the ones visible in this image help distribute the iron offshore, where it mixes with nitrate-rich waters. As a result, conditions are just right for an offshore bloom of phytoplankton. The bloom is visible here as swirls of green.
- Runoff is highest from June through September. By fall, iron still makes its way into Gulf of Alaska, but it takes a different path. Low river levels in the fall mean that more riverbed sediments are exposed to winds. Winds can loft huge plumes of riverbed dust into the air, some of which settles back down on gulf waters and fertilizes blooms.
Figure 33: The VIIRS instrument on Suomi NPP captured this image of the Gulf of Alaska on June 9, 2016 (image credit: NASA Earth Observatory, image by Norman Kuring)
• June 15, 2016: The Suomi NPP satellite collected this natural-color image with the VIIRS (Visible Infrared Imaging Radiometer Suite) instrument which detected hundreds of fires burning in Central Africa on June 13, 2016 (Figure 34). Actively burning areas, detected by MODIS's thermal bands, are outlined in red. Each hot spot is an area where the thermal detectors recognized temperatures higher than background. The location, widespread nature, and number of fires suggest that these fires were deliberately set to manage land. Farmers often use fire to return nutrients to the soil and to clear the ground of unwanted plants. 47)
Figure 34: Fires in Central Africa acquired with VIIRS on Suomi NPP on June 13, 2016 (image credit: NASA, image of Jeff Schmaltz)
• Light Pollution, June 10, 2016: The Milky Way, the brilliant river of stars that has dominated the night sky and human imaginations since time immemorial, is but a faded memory to one-third of humanity and 80 percent of Americans, according to a new global atlas of light pollution produced by Italian and American scientists. The atlas takes advantage of low-light imaging now available from the NOAA/NASA Suomi -NPP (National Polar-orbiting Partnership) satellite, calibrated by thousands of ground observations. 48) 49)
- Light pollution is one of the most pervasive forms of environmental alteration. In most developed countries, the ubiquitous presence of artificial lights creates a luminous fog that swamps the stars and constellations of the night sky. "We've got whole generations of people in the United States who have never seen the Milky Way," said Chris Elvidge, a scientist with NOAA's National Centers for Environmental Information. "It's a big part of our connection to the cosmos — and it's been lost."
- Elvidge, along with Kimberly Baugh of NOAA's Cooperative Institute for Research in Environmental Sciences, is part of a team that developed a global atlas of light pollution published in the journal Science Advances. Using high-resolution satellite data and precision sky brightness measurements, their study produced the most accurate assessment yet of the global impact of light pollution.
- Light pollution is most extensive in countries like Singapore, Italy and South Korea, while Canada and Australia retain the most dark sky. In Western Europe, only small areas of night sky remain relatively undiminished, mainly in Scotland, Sweden and Norway. Despite the vast open spaces of the American west, almost half of the U.S. experiences light-polluted nights.
- "In the U.S., some of our national parks are just about the last refuge of darkness – places like Yellowstone and the desert southwest," said co-author Dan Duriscoe of the National Park Service. "We're lucky to have a lot of public land that provides a buffer from large cities."
- Light pollution does more than rob humans of the opportunity to ponder the night sky. Unnatural light can confuse or expose wildlife 50) like insects, birds and sea turtles 51), often with fatal consequences.
• May 2016: Preparation for Emergency Conjunction Avoidance Maneuvers for the Suomi NPP mission. In January 2014, the Suomi NPP MOT (Mission Operations Team) responded to several close approaches. The MOT started RMM (Risk Mitigation Maneuver) planning for four threats during this period. Three of these events did not lead to an executed RMM due to dissipated threat levels from new tracking data. At the moment when these events were cancelled, the MOT had completed most of the steps needed to make an RMM ready for execution. 52)
- Preparation for an RMM demands a significant resource and time allocation from the Suomi NPP MOT, which requires significant lead times and limits the MOT's ability respond to several close approaches simultaneously. Suomi NPP operates at an altitude of approximately 824 km which is identified to be a dense and potentially hazardous debris environment. Due to this dense environment, the MOT experiences frequent close approach events. It was soon realized that the MOT needed improved tools and processes to optimize RMM planning and reduce response times to close approach events. Reducing response times is necessary as better detection capabilities in the near future are expected to increase the number of predicted close approaches.
- The MOT typically executes an RMM twelve to twenty four hours before the TCA (Time of Closest Approach) to minimize the size of the avoidance maneuver. The current method takes approximately twenty hours or two business days of preparation prior to executing the maneuver, requiring the RMM process to be started approximately seventy-two hours before TCA. Additional tracking is required to reduce uncertainties in the position of the approaching object, which is taking place during the period that the MOT is preparing the maneuver. The largest step in the process is the creation, validation, and testing of the DAS (Detailed Activity Schedule) command load containing the commands to execute an RMM. This step requires roughly ten to twelve hours of time to accomplish and required each burn time and duration to be tested using an aging simulator.
- Creating a method of executing an RMM using pre-verified maneuver sequences stored on the spacecraft will remove this ten- to twelve-hour step from the process, allowing more time for uncertainties to reduce prior to responding, and will remove the dependency on a single point of failure simulator and mission planning system resources.
- The OSMS (Onboard Stored Maneuver Sequence) system uses a set of on-board CBM (Command Block Memory) sequences, a sequence of relative time commands, and a set of ground system scripts to command an RMM without the need for a DAS. This system was put through a period of ground testing and on-orbit testing and integration. Once declared operational, this system will significantly improve how much time is needed to execute an RMM.
- The OSMS system consists of components for the spacecraft and ground system. The spacecraft portions of the system are a series of CBM sequences containing all instructions for executing an RMM. The ground components of the system are comprised of ground scripts that will configure and execute the on-orbit CBM sequences.
- The on-orbit CBM is made up of four sequences. Two sequences consist of maneuver commands for the spacecraft, each covering one of the two delta-V modes. The two other sequences contain the commands to prepare the CERES (Clouds and the Earths Radiant Energy Systems) and OMPS instruments for a maneuver and return both instruments to science mode following the RMM. Each maneuver sequence has two sections. The first section is a series of configurable slots that the ground scripts will populate with time delays appropriate for placing the delta-v burn of the RMM at the desired time. The second section contains the maneuver sequence. In the maneuver sequence, there are three empty slots that are populated by the ground scripts. The first two slots are reserved for CBM execution commands for the CERES and OMPS sequences. The third slot is reserved for the delta-v burn command and is populated with the appropriate command and desired magnitude for the burn.
- The ground portion of the system consists of two scripts. The first script will ask the user when the ΔV burn of the RMM should be scheduled, the duration of the burn in milliseconds, and whether CERES and OMPS should be configured for the maneuver. After taking into account the user inputs, it will:
1) Select the delta-v burn mode based on requested duration
2) Calculate the delay needed to place the burn as requested by the user
3) Insert the needed delays in the delay section of the maneuver CBM
4) Insert the CBM calls for the CERES and OMPS sequences
5) Insert the burn command with the appropriate magnitude based on selected burn duration
6) Execute the maneuver CBM sequence.
- The second script, the back out script, will clean up the maneuver CBM sequences and conduct a check to confirm the on-orbit CBM is in its pre-maneuver configuration.
Before the OSMS system could be declared operational, a series of tests had to be performed. The MOT developed a set of ground and on-orbit tests to validate OSMS.
Ground Test Results: All post-test artifacts from the ground test sets were reviewed by the MOT. Analysis of the simulator command logs confirmed that all OSMS CBM sequences executed in their proper order and at the requested times. All burn options were proven valid after comparing test results with predicted results. Command logs and ground system logs confirmed that the setup and back out scripts performed as desired. After reviewing results, it was concluded that all OSMS components were ready to be deployed to the operational ground system and uplinked to the spacecraft.
On-Orbit Test Results: At the time of paper submission, the no-burn and open-loop mode tests have been successfully performed. The no-burn test was performed on November 18, 2015. The no-burn test confirmed that the OSMS ground scripts would perform properly on the operational ground system and placed all commands within two seconds of their desired times. The open-loop test was performed on February 24, 2016, but due to ground track restrictions, the closed-loop test will not be performed for several months. During the open-loop test, OSMS performed DMU (Drag Makeup Maneuver) 22 and placed all commands within one second of their desired execution times. Despite the lack of closed-loop maneuver testing, the no-burn and open-loop test confirmed that the OSMS system can command an RMM without the need for the creation, validation, and testing of a DAS.
In summary, the results gathered so far show promise for the OSMS system. All time delays and burn options were validated, removing the need to simulate future maneuvers. The OSMS system can perform open-loop burn RMMs without the need for a DAS. Once the closed-loop test can be completed, the need for a DAS for RMM execution can be safely removed. Removing the need for creating, validating, and testing the DAS will eliminate ten to twelve hours of RMM preparation time and lower the total time to respond to an RMM from two days to less than one day. With a less than one-day response time, the MOT can delay the start of RMM preparations. The delay will allow time for additional tracking information to be received, reducing positional uncertainty in the approaching object and reducing the calculated risk of conjunction. Reduced risk of conjunction/collision often eliminates the need for executing the maneuver, saving the team the time and effort of a planning exercise for an event that is not executed.
• May 3, 2016: The Taklimakan (Taklamakan) desert in China is one of the driest, most barren expanses on Earth. Flanked by mountain ranges on three sides and parched by the resulting rain shadow, parts of the Tarim Basin receive no more than 10 mm of rain per year. It is no surprise that plant life is scarce. With little vegetation to hold sand in place, some 85% of the Taklimakan consists of shifting sand dunes. Only the dune fields of Saudi Arabia's Rub' al Khali cover a larger area. Taklimakan's dunes can soar up 200 to 300 meters. With so much sand and so little vegetation or moisture, dust storms are a regular occurrence, particularly in the spring. 53)
- The Tarim Basin is bordered by the Kunlun Shan mountains to the south and the Tian Shan mountains to the north (the Tian Shan is covered with snow and partly obscured by clouds in this image of Figure 35) . The basin opens up on its eastern edge, but that is not generally a way out for dust. Prevailing low-altitude winds almost always blow from the east, keeping most dust below 5 km—about the height of the mountain ranges—and trapped within the basin. In spring, strong surface winds can sometimes lift dust up to 10 km. These particles can then be transported by higher-altitude winds that send them across China and the Pacific. In this case, however, the dust appears to be relatively low in the atmosphere.
Figure 35: On May 1, 2016, the VIIRS (Visible Infrared Imaging Radiometer Suite) on the Suomi NPP satellite captured this natural-color image of northeasterly winds pushing a wall of dust southwest across the Tarim Basin (image credit: NASA Earth Observatory, image by Jeff Schmaltz)
• On March 6, 2016, news and social media was buzzing with spectacular photographs of the northern lights (aurora borealis) painting skies across the United Kingdom with brilliant shades of green and pink. — The event was impressive from above as well. Using the DNB (Day-Night Band ) of VIIRS (Visible Infrared Imaging Radiometer Suite), the Suomi NPP satellite acquired this view of the aurora borealis on March 7, 2016. Auroras appear as white streaks over Iceland, the North Atlantic, and Norway. The DNB sensor detects dim light signals such as airglow, gas flares, city lights, and reflected moonlight. In the image of Figure 36, the sensor detected the visible light emissions that occur when energetic particles rain down from Earth's magnetosphere into the gases of the upper atmosphere. 54)
- It is not often that the northern lights are visible south of Scotland and Northern Ireland, but a geomagnetic storm colored night skies over a much wider swath of the country. The storm reached a G3 or "severe" level on NOAA's geomagnetic storm scale, according to the Space Weather Prediction Center. On March 7, the Kp index—a metric for global geomagnetic storm activity—rose as high as 7 on a scale that goes to 9.
- The brilliant colors of the aurora are provoked by activity the Sun: Solar energy and particles speed toward Earth in a steady stream called the solar wind, or they rush out in massive eruptions known as CMEs (Coronal Mass Ejections). These storms from the Sun disturb geospace (the space around Earth) and energize particles already trapped in the magnetosphere and radiation belts. Electrons then race down Earth's magnetic field lines and crash into the gases at high altitudes of the atmosphere. Oxygen gives off a green color when excited; nitrogen produces blue or red colors.
Figure 36: The VIIRS instrument of Suomi NPP acquired this image of the aurora borealis on March 7, 2016 (image credit: NASA Earth Observatory , Adam Volland)
• January 27, 2016: It's wintertime in the Northern Hemisphere, which means spectacular phytoplankton blooms return to the Arabian Sea. Blooms show up this time of year in the Arabian Sea because of the winter monsoon. Winds shift from southwesterly to northeasterly, stirring up currents that bring nutrients up from the depths and out from coastal tributaries. The change in wind direction also picks up dust from the arid lands of southwestern Asia, carrying it out over the sea. This dust contains mineral nutrients that phytoplankton need to fuel their growth. 55)
- Dust storms help fertilize the ocean. They move nitrate, phosphate, and iron from the land into ocean surface waters around the world. Research published in October 2014 found that winter blooms in the Arabian Sea could occasionally be attributed to the nutrients received from dust storms like this one.
Figure 37: VIIRS on Suomi NPP acquired on Dec. 21, 2015 this image of a phytoplankton bloom off the coast of Oman (left), Pakistan (center), and India (right), image credit: NASA Earth Observatory, Norman Kuring
Legend to Figure 37: The image was composed with data from the red, green, and blue bands from VIIRS, in addition to chlorophyll data. A series of image-processing steps were then applied to highlight color differences and bring out the bloom's more subtle features.
• Dec. 1, 2015: The composite visible image of Figure 38 shows a thick line of agricultural fires stretching from west to east across Central Africa. Visible-light images were taken from the VIIRS instrument aboard the Suomi NPP satellite on Nov. 27, 2015 at 12:50 UTC. The VIIRS image showed the heat signatures from fires (in red) from Burkina Faso and northern Ghana, Togo and Benin stretch eastward across southern Nigeria, Chad and Sudan, Cameroon, Central Africa Republic, South Sudan and Ethiopia. 56)
Figure 38: A line of fires seen by the VIIRS instrument on the Suomi NPP satellite on Nov. 27, 2015 (image credit: NASA/GSFC, Jeff Schmaltz)
• On October 28, 2015, the joint NOAA/NASA Suomi NPP mission is 4 years on orbit providing successful observations. The mission was declared the primary satellite for weather in May of 2014. — As of August 31, 2015, Suomi NPP has orbited the Earth 19,900 times, and provided 4.9 PB of data archived in the NOAA CLASS (Comprehensive Large Array-data Stewardship System) archive. This data provides weather and environmental data for a wide variety of forecasting, monitoring and assessment needs. The Suomi NPP ATMS data were operationally assimilated by the NOAA Centers for Environmental Prediction within 7 months of the Suomi NPP launch, three times faster than any prior POES (Polar-orbiting Operational Environmental Satellite) microwave sounder. CrIS was operationally assimilated within 13 months, also setting a new record for infrared sounder assimilation. CrIS would have been assimilated within 9 months; however, the operational assimilation was delayed by supercomputer upgrades and hurricane season freezes which delayed changes in the assimilation system. Suomi NPP data can be obtained without any restrictions from: http://www.class.ncdc.noaa.gov/saa/products/welcome 57)
- The Suomi NPP satellite has been working very well. There are a few anomalies that recur, however these do not significantly impact operations or data availability. The program is closely monitored for system health. In addition, the program has established a longevity plan to guide risk mitigation efforts to realize the maximum life possible. One mitigation measure has been implemented into operations on the ATMS instrument.
- Data availability has been outstanding, as shown in Figure 39, even though the initial version of the ground segment is aged and has relatively limited capabilities. This performance is a strong testament to the efforts of the JPSS (Joint Polar Satellite System) ground project team.
Figure 39: Suomi NPP mission data availability summary (image credit: NOAA)
- When Suomi NPP was launched, CrIS was operated in a reduced spectrum mode because in the early phase of NPOESS the success of carbon monoxide and other trace gas products from similar precursor instruments, such as NASA's AIRS (Atmospheric InfraRed Sounder ) were unknown. Both were also operated at the lower data rate because there concerns about margin in the on-board data bus. - Following on-orbit and ground test activities, CrIS full spectrum capability was implemented in December 2014, and OMPS full data rate has been prepared for implementation in 2016.
- Another major operational improvement for users has been the demonstration of direct readout. NOAA was provided additional funding following the super-storm Sandy (hurricane Sandy was he deadliest and most destructive hurricane of the 2012 Atlantic hurricane season) to make several investments that will provide mitigation of impacts in the event of a gap in afternoon polar weather satellite observations. One of the investments has been to upgrade NOAA direct readout terminals to handle the X-band feed from Suomi NPP and the subsequent JPSS missions as well all of the heritage POES and EUMETSAT sounder data. The purpose of this is to provide an alternative avenue to retrieve data with very low latency to feed to the Numerical Weather Program.
• August 21, 2015: In the summer of 2015, wildfires raged across the western United States and Alaska. Many of those fires burned in the U.S. Northwest, visible in Figure 40 from late August, 2015. According to the Northwest Interagency Coordination Center, the Okanogan Complex Fire in Washington was among the larger active fires; as of August 20, the fire had burned 91,314 acres (370 km2). In Oregon, the Canyon Creek Complex Fire had burned 48,201 acres (195 km2), destroyed 26 residences and threatened another 500. Both fires were less than 40 percent contained. Meanwhile, firefighters have made progress on the large, damaging Cornet-Windy Ridge Fire in Oregon, which as of August 20 was 70 percent contained. 58)
Figure 40: This image was acquired in the early morning local time on August 19, 2015 with the VIIRS (Visible Infrared Imaging Radiometer Suite) sensor on the Suomi NPP satellite. The image was made possible by the instrument's "day-night band," which uses filtering techniques to observe dim signals including those from wildfires. Labels point to the large, actively burning fires in the region (image credit: NASA)
• Aug. 6, 2015: The NOAA/NASA Suomi NPP satellite passed over powerful Typhoon Soudelor when it was headed toward Taiwan. The VIIRS instrument aboard Suomi NPP captured an infrared image of the typhoon. The infrared image showed some thunderstorms within the typhoon with very cold cloud top temperatures, colder than -53ºC. Temperatures that cold stretch high into the troposphere and are capable of generating heavy rain.
Figure 41: VIIRS image of Typhoon Soudelor, acquired on August 7 (UTC), 2015 when it was headed toward Taiwan (image credit: UWM/CIMSS/SSEC, William Straka III)
• May 26, 2015: Physical oceanographers will sometimes point out that the ocean has weather and seasons, much like the atmosphere. Masses of water with different temperatures, salinities, and nutrient levels clash and mix like warm and cold fronts in the air. Different plant-like species—phytoplankton—bloom, spread, and die back with the different conditions. Ocean currents swirl in turbulent fronts and eddies—much like tornadoes and hurricanes, though far more productive than destructive.
- Springtime in the North Atlantic Ocean is a time of great change, turbulence, and productivity. Increasing sunlight, nutrient runoff from land and upwelling from the deep, and changeable atmospheric weather all conspire to color the ocean surface with interesting patterns. The composite image (Figure 42) shows the northwest Atlantic Ocean on May 14, 2015, with the New England and Canadian Maritimes in the background. The image was constructed from data acquired by VIIRS (Visible Infrared Imaging Radiometer Suite) sensor on the Suomi NPP satellite. Colors were enhanced to make the blooms more visible. 59)
Figure 42: Composite image of the VIIRS instrument of the northwest Atlantic Ocean, acquired on May 14, 2015 (image credit: NASA Earth Observatory, Norman Kuring)
Legend to Figure 42: On the left side of the image, several circular patterns are traced out by the light green phytoplankton near the surface. These rings are likely eddies that have spun off of the Gulf Stream, which turns east toward Europe in this region. The underwater plateau known as George's Bank is also made visible (indirectly) by the plankton. The Labrador Current and the Gulf Stream meet in this area, and the relatively shallow water promotes an abundant crop of phytoplankton, marine plants, shellfish, finfish, and marine mammals, all the way up the food chain. The bank is marked by bright swirls of color in the image.
Patches and swirls of phytoplankton continue to the north and east from the bank, indicating regions where there are significant nutrients near the surface and other water conditions that promote blooms. Though it is very difficult to identify the genus and species of phytoplankton from a satellite, researchers working from ships in the North Atlantic confirmed that at least some of the phytoplankton blooming in May were diatoms, including Guinardia delicatula.
The Gulf of Maine and George's Bank have historically been some of the most productive fishing grounds on the planet. Overfishing and pollution brought significant declines in the late 20th century, though regulation and changes in fishing practices may now restore some of the abundance in the local waters. Researchers from the Woods Hole Oceanographic Institution, North Carolina State University, and NOAA have been regularly monitoring the region with ship-based studies, ocean models, and automated, moored instruments in order to keep track of phytoplankton and algae species, particularly those that lead to toxic algae blooms.
• Feb. 25, 2014: In late February 2015, a significant winter storm stirred up dust and sand across much of the Arabian Peninsula. The low-pressure system energized strong northwest winds that carried dust from as far as northern Saudi Arabia, Iraq, and Kuwait to the shores of the Persian Gulf and the Arabian Sea. 60)
- The VIIRS ( Visible Infrared Imaging Radiometer Suite) on the Suomi NPP satellite captured these images of the sand storm on February 23 and 24. Because of the desert landscape and the widespread nature of the event, the airborne particles are easier to see over open water (Figure 43).
- Sand storms are common in the region at this time of year, though this one seems particularly potent and long-lasting—five days so far. Poor visibility has been the biggest danger, causing hundreds of automobile accidents across Oman, Saudi Arabia, and the UAE (United Arab Emirates). Visibility dropped as low as 500 m at Al Maktoum International Airport in Dubai.
- The weather system brought rain and snow to several locations, and rough seas along the coast. Temperatures in Muscat, Oman, dropped from 38ºC on February 20 to 20°C on February 24. The city of Dubai (UAE) deployed thousands of workers to clear dust and debris from the streets. News reports said more than 21 tons of sand had been cleared from the city alone. Government authorities in several countries warned people to stay inside as much as possible and to cover their noses and mouths when walking outside. The storms are a particular danger to people with asthma and other respiratory diseases.
Figure 43: VIIRS image of the persistent sand storm on the Southern Arabian Peninsula acquired on Feb. 24, 2015 (image credit: NASA Earth Observatory, Jesse Allen)
• Debris avoidance maneuver for Suomi NPP: — The Suomi NPP mission team monitored a possible close approach of a debris object on Sept. 28, 2014. The risk was assessed to be high enough to start planning a spacecraft maneuver to put the satellite into a safer zone, out of the path of the object classified in a size range of 10 cm up to 1 m. 61)
- It was determined that the object (travelling at almost 27,400 km/h) was approaching at a nearly "head on" angle, and could potentially only miss the Suomi NPP satellite by approximately 100 m on Sept. 30, if no action was taken. With that knowledge, the decision was made on Sept. 29, for NSOF (NOAA's Satellite Operations Facility) in Suitland, Maryland, to reposition Suomi NPP. Operational control as well as planning and execution of all Suomi NPP maneuvers take place at NSOF.
- Since Suomi NPP's launch in October 2011, this recent reposition was the fourth Risk Mitigation Maneuver to avoid space debris. In this case, the object was a section of a Thorad-Agena launch vehicle used between 1966 and1972 primarily for Corona U.S. reconnaissance satellites.
- A previous Suomi NPP risk mitigation maneuver in January 2014 avoided a discarded booster from a Delta 1 launch vehicle, a type of rocket made in the United States for a variety of space missions from 1960 to 1990. There is also a significant amount of debris in Suomi NPP's orbit from the Chinese Fengyun-1C, a meteorological satellite China destroyed in January 2007 in a test of an anti-satellite missile. Another threat near Suomi NPP's orbit is the debris resulting from a 2009 collision of a functioning commercial communications satellite and a defunct Russian satellite.
• Sept. 25, 2014: A joint NOAA/NASA satellite is one of several satellites providing valuable information to aviators about volcanic hazards. An aviation "orange" alert was posted on August 18, 2014, for Bárðarbunga, a stratovolcano located under the Vatnajökull glacier in Iceland, indicating the "volcano shows heightened or escalating unrest with increased potential of eruption." 62)
Much of the information leading to that alert came from satellites including VIIRS (Visible Infrared Imaging Radiometer Suite) instrument on board the Suomi NPP spacecraft. The VIIRS instrument is suited to detect the relatively unique spectral signature difference of volcanic clouds often absorb and reflect radiation as a function of wavelength in a manner that is very different from other cloud types.
• July 5, 2014: Large amounts of Saharan sand began to arrive in the Americas in June 2014. On June 23, a lengthy river of dust from western Africa began to push across the Atlantic Ocean on easterly winds. A week later, the influx of dust was affecting air quality as far away as the southeastern United States. The image of Figure 44 was released on July 5, 2014 in NASA's Earth Observatory series. 63)
Figure 44: The composite image, acquired with data from VIIRS on Suomi NPP, shows dust heading west toward South America and the Gulf of Mexico on June 25, 2014 (image credit: NASA Earth Observatory)
Legend to Figure 44: The dust flowed roughly parallel to a line of clouds in the intertropical convergence zone, an area near the equator where the trade winds come together and rain and clouds are common. Saharan dust has a range of impacts on ecosystems downwind. Each year, dust events like the one pictured here deliver about 40 million tons of dust from the Sahara to the Amazon River Basin. The minerals in the dust replenish nutrients in rainforest soils, which are continually depleted by drenching, tropical rains. Research focused on peat soils in the Everglades show that African dust has been arriving regularly in South Florida for thousands of years as well.
In some instances, the impacts are harmful. Infusion of Saharan dust, for instance, can have a negative impact on air quality in the Americas. And scientists have linked African dust to outbreaks of certain types of toxic algal blooms in the Gulf of Mexico and southern Florida.
• December 2013: NASA scientists have revealed the inner workings of the ozone hole that forms annually over Antarctica and found that declining chlorine in the stratosphere has not yet caused a recovery of the ozone hole. — More than 20 years after the Montreal Protocol agreement limited human emissions of ozone-depleting substances, satellites have monitored the area of the annual ozone hole and watched it essentially stabilize, ceasing to grow substantially larger. However, two new studies show that signs of recovery are not yet present, and that temperature and winds are still driving any annual changes in ozone hole size. 64)
Figure 45: The area of the ozone hole, such as in October 2013, is one way to view the ozone hole from year to year. However, the classic metrics have limitations (image credit: NASA, Ozone Hole Watch)
The 2012 ozone hole was the second-smallest hole since the mid 1980s. To find out what caused the hole's diminutive area, the researchers, Susan Strahan and Natalya Kramarova, turned to data from the NASA-NOAA Suomi National Polar-orbiting Partnership satellite, and gained a first look inside the hole with the satellite's OMPS (Ozone Mapping and Profiler Suite). Next, data were converted into a map that shows how the amount of ozone differed with altitude throughout the stratosphere in the center of the hole during the 2012 season, from September through November.
The map revealed that the 2012 ozone hole was more complex than previously thought. Increases of ozone at upper altitudes in early October, carried there by winds, occurred above the ozone destruction in the lower stratosphere.
The classic metrics create the impression that the ozone hole has improved as a result of the Montreal protocol. In reality, meteorology was responsible for the increased ozone and resulting smaller hole, as ozone-depleting substances that year were still elevated. The study has been submitted to the journal of Atmospheric Chemistry and Physics (Ref. 64).
Figure 46: A look inside the 2012 ozone hole with the Ozone Mapper and Profiler Suite shows how the build-up of ozone (parts per million by volume) in the middle stratosphere masks the ozone loss in the lower stratosphere (image credit: NASA)
• December 2013: Daytime measurements of reflected sunlight in the visible spectrum have been a staple of Earth-viewing radiometers since the advent of the environmental satellite platform. At night, these same optical-spectrum sensors have traditionally been limited to thermal infrared emission, which contains relatively poor information content for many important weather and climate parameters. These deficiencies have limited our ability to characterize the full diurnal behavior and processes of parameters relevant to improved monitoring, understanding and modeling of weather and climate processes. Visible-spectrum light information does exist during the nighttime hours, originating from a wide variety of sources, but its detection requires specialized technology. Such measurements have existed, in a limited way, on USA Department of Defense satellites, but the Suomi NPP satellite, which carries a new Day/Night Band (DNB) radiometer, namely VIIRS, offers the first quantitative measurements of nocturnal visible and near-infrared light. 65)
- VIIRS includes a high-sensitivity DNB that is panchromatic (sensitive to all visible colors) and collects highly detailed imagery of the Arctic even under low light levels (Figure >47). VIIRS DNB imagery has vastly superior information content compared with emissive or thermal IR imagery collected at the same time under the very low thermal contrast conditions that occur frequently in the Arctic during winter (Figure 48). The imagery is enabling significant improvements in forecasting weather and sea ice changes. 66)
Figure 47: VIIRS image of of Alaska and the Chukchi and Beaufort Seas taken under moonlight. DNB provides high-contrast imagery even under the low thermal contrast conditions prevalent in the Arctic winter [image credit: NOAA/CIRA (NOAA/Cooperative Institute for Research in the Atmosphere)at Colorado State University)]
Figure 48: VIIRS imagery in the MI5 spectral band (left) and the DNB (right) of the western Chukchi Sea. Note how the sea ice structure and other surface detail so readily apparent in the DNB image is not visible at all in the thermal IR image (image credit: NOAA/CIRA)
• Aug. 2013: Tracking of the Chelyabinsk Meteor Plume. On Feb. 15, 2013, a meteor (or meteoroid) with a mass of ~ 10,000 tons exploded above the Russian city of Chelyabinsk. Travelling at a speed of ~18 km/s, the meteoroid quickly became a brilliant fireball as it passed over the southern Ural region, exploding in an air burst over Chelyabinsk. The atmosphere absorbed most of the released energy, which was equivalent to nearly 500 kilotons of TNT making it ~30 times more powerful than either of the atomic bombs detonated at Hiroshima and Nagasaki. About 1,500 people were injured, Over 4,300 buildings in six cities across the region were damaged by the explosion. 67)
- Some of the surviving pieces of the Chelyabinsk bolide (meteor) fell to the ground. But the explosion also deposited hundreds of tons of dust up in the stratosphere, allowing a NASA satellite to make unprecedented measurements of how the material formed a thin but cohesive and persistent stratospheric dust belt. 68) 69)
About 3.5 hours after the initial explosion, the OMPS (Ozone Mapping Profiling Suite) instrument's limb profiler on the NASA/NOAA Suomi NPP spacecraft detected the plume high in the atmosphere at an altitude of about 40 km, quickly moving east at more than 300 km/h. The day after the explosion, the satellite detected the plume continuing its eastward flow in the jet stream and reaching the Aleutian Islands. Larger, heavier particles began to lose altitude and speed, while their smaller, lighter counterparts stayed aloft and retained speed – consistent with wind speed variations at the different altitudes.
By Feb. 19, 2013, four days after the explosion, the faster, higher portion of the plume had snaked its way entirely around the Northern Hemisphere and back to Chelyabinsk. But the plume's evolution continued: At least three months later, a detectable belt of bolide dust persisted around the planet.
The scientists' model simulations, based on the initial Suomi NPP observations and knowledge about stratospheric circulation, confirmed the observed evolution of the plume, showing agreement in location and vertical structure.
Figure 49: Model and satellite data show that four days after the bolide explosion, the faster, higher portion of the plume (red) had snaked its way entirely around the northern hemisphere and back to Chelyabinsk, Russia (image credit: NASA/GSFC)
• July/August, 2013: Each year, hundreds of millions of tons of dust are picked up from the deserts of Africa and blown across the Atlantic Ocean (Figure 50). That dust helps build beaches in the Caribbean and fertilizes soils in the Amazon region. It affects air quality in North and South America. And some say dust storms might play a role in the suppression of hurricanes and the decline of coral reefs. 70)
Figure 50: Tracking dust across the Atlantic: the image was aquired by the VIIRS instrument on July 31, 2013 (image credit: NASA)
Legend to Figure 50: Dust from the Sahara Desert and other points in interior Africa were lofted into the sky in late July 2013. Figure 50 shows the general westerly and northwesterly progression of the airborne particles across the Atlantic Ocean. (Note that the milky lines running vertically across each image are caused by sunglint, the reflection of sunlight off the ocean directly back at the sensor.) Such an image helps to reveal wind patterns (trade winds) that steer plumes and clouds. At several points, dust stretched continuously from North Africa to South America.
The dust also was detected by the OMPS (Ozone Mapping Profiling Suite) on Suomi NPP. The maps of Figure 51 show the relative concentrations of aerosol particles on July 31 and August 1-2, 2013. While designed to measure ozone in the atmosphere, OMPS gathers ultraviolet spectral information that reveals the presence of smoke and airborne dust. Lower concentrations appear in yellow, and greater concentrations appear in orange-brown. Each map includes roughly six satellite passes. Note: sunglint also causes some vertical banding in these images.
Dust has long blown across the Atlantic from Africa, but only during the past several decades of satellite observations have meteorologists begun to appreciate the vast scale of these events. While estimates of the dust transported run to hundreds of millions of tons per year, humankind still knows relatively little about the effects on phytoplankton productivity, climate, and human health. 71)
Figure 51: The 3 images show the Saharan dust storm of the OMPS instrument acquired on July 21 to August 2, 2013 (image credit: NASA)
Table 6: First results of a long-term VIIRS LST (Land Surface Teperature) validation 72)
Figure 52: Schematic description of a USCRN (US Climate Reference Network) station (image credit: NOAA, NASA)
• June 21, 2013: Images crafted from a year's worth of data collected by the Suomi NPP satellite, provide a vivid depiction of worldwide vegetation (Figure 53). The image, provided by NASA and NOAA on June 19, 2013, shows the difference between green and arid areas of Earth as seen in data from the VIIRS (Visible-Infrared Imager/Radiometer Suite) instrument aboard Suomi NPP. VIIRS detects changes in the reflection of light, producing images that measure vegetation changes over time. 73) 74) 75)
Vegetation Index: There are many types of indices that measure vegetation and many are calculated by using satellite data to compare the relative difference between how much energy is absorbed by the land surface versus how much is reflected back into space. Plants absorb visible light to undergo photosynthesis, so when vegetation is lush, nearly all of the visible light is absorbed by the photosynthetic leaves, and much more near-infrared light is reflected back into space. However for deserts and regions with sparse vegetation, the amount of reflected visible and near-infrared light are both relatively high. The VIIRS sensor on the Suomi NPP satellite is sensitive to these different types of visible and near-infrared light.
Figure 53: Vegetation as seen by Suomi NPP (image credit: NASA/NOAA)
Suomi NPP continues the observations of Earth from space that were pioneered by NASA's Earth Observing System. The satellite's five instruments are providing scientists with data to extend more than 30 key long-term datasets. These records, which include observations of the ozone layer, land cover, atmospheric temperatures and ice cover, provide critical data for global change science.
Suomi NPP also collects critical data for our understanding of long-term climate change while increasing our ability to improve weather forecasts in the short term. NOAA meteorologists are incorporating Suomi NPP information into their weather prediction models to produce forecasts and warnings that already are helping emergency responders anticipate, monitor, and react to many types of natural events.
• VIIRS instrument calibration: 78)
- VIIRS continues to operate and calibrate satisfactorily (as planned and expected)
- Overall on-orbit performance meets the design requirements (such as SNR/NEdT)
- Continuous and dedicated calibration efforts are critical for maintaining SDR data and calibration quality
- The modulated RSR, as a result of mirror degradation, have been developed and applied to sensor SDR calibration and data production.
• December 05, 2012: Scientists unveiled an unprecedented new look at our planet at night at the American Geophysical Union meeting in San Francisco, CA. A global composite image, constructed using cloud-free night images from the Suomi NPP satellite, shows the glow of natural and human-built phenomena across the planet in greater detail than ever before. 79)
Figure 54: Composite map of the world assembled from data acquired by the Suomi NPP satellite in April and October 2012 (image credit: NASA Earth Observatory/NOAA NGDC)
Figure 55: This image of the continental United States at night is a composite assembled from data acquired by the Suomi NPP satellite in April and October 2012 (image credit: NASA Earth Observatory/NOAA NGDC, Ref. 79)
Legend to Figure 55: The image was made possible by the satellite's "day-night band" of the VIIRS (Visible Infrared Imaging Radiometer Suite) instrument, which detects light in a range of wavelengths from green to near-infrared and uses filtering techniques to observe dim signals such as city lights, gas flares, auroras, wildfires and reflected moonlight.
• On October 28, 2012, Suomi NPP celebrated its first anniversary on orbit. 80)
• October 2012: Hurricane Sandy (also referred to as Superstorm Sandy) made landfall along the southern New Jersey coast on the evening of Oct. 29, 2012. The Suomi NPP satellite acquired the accompanying image (Figure 56) of the storm around 3:35 a.m. Eastern Daylight Time on October 30 (UTC 7:35 hours on Oct. 30). The full moon, which exacerbated the water height at the time of the storm surge, lit up the tops of the clouds. 81)
Sandy's clouds stretched from the Atlantic Ocean westward to Chicago. Clusters of lights gave away the locations of cities throughout the region, but along the East Coast, clouds obscured city lights, many of which were out due to the storm. On October 30, CNN reported that several millions of customers in multiple states were without electricity.
On Nov. 1, 2012, the reported death toll from hurricane Sandy's flooding and high winds has now reached 160 (88 in the U.S., 54 in Haiti, 11 in Cuba), with first damage estimates ranging from $20 – $55 billion. 82)
Figure 56: Suomi NPP VIIR (Visible Infrared Imaging Radiometer Suite) image of Hurricane Sandy on Oct. 30, 2012 (image credit: NASA)
Figure 57: Suomi NPP VIIRS true-color imagery from bands M3–M5, composited from three consecutive daytime passes on 17 June 2012, shows the continental United States and surroundings in vivid color detail (image credit: NOAA) 84)
• In July 2012, Suomi NPP started the Direct Broadcast Service with the HRD (High Rate Data) link. Direct Broadcast data is unique in that it provides real-time data on a regional basis which enables quick evaluation of events at a local level. Researchers world-wide are then able to use customized algorithms, or mathematical formulas, turning raw data into images to help manage quickly changing regional events, such as rapidly spreading forest fires, rushing flood waters and floating icebergs at the poles that could affect the shipping and fishing industries. 85)
Ultimately, Suomi NPP's direct broadcast data does two things: continue NASA's role in data continuity by picking up where MODIS will leave off, and enable users to pluck data that is of importance to them from the reservoir of information that comes down from Suomi NPP.
The DRL (Direct Readout Laboratory) at NASA/GSFC organizes and manages the funneling of data to the roughly 200 ground stations around the world that will use it. The DLR also provides the user community with a baseline processing system called IPOPP (International Polar Orbiter Processing Package). This framework is a real-time data processing system that enables the user community to process, generate and visualize direct broadcast data as it is transmitted to Earth (Ref. 85).
• In early March 2012, NASA has completed commissioning of the Suomi NPP spacecraft and its sensor complement. With the completion of commissioning activities, operation of the Suomi NPP has now been turned over to the JPSS (Joint Polar Satellite System) team. NOAA's JPSS Program provided three of the five instruments and the ground segment for Suomi NPP. A government team from the NOAA Satellite Operations Facility in Suitland, Md., will operate the satellite.86) 87)
• In February 2012, the CrIS (Cross-track Infrared Sounder) became operational. Hence, CrIS is joining the other four instruments aboard the Suomi NPP spacecraft. 88)
Figure 58: The ozone suite on Suomi NPP continues more than 30 years of ozone data (image credit: NASA)
Legend to Figure 58: The image shows the thickness of the Earth's ozone layer on January 27th from 1982 to 2012. This atmospheric layer protects Earth from dangerous levels of solar ultraviolet radiation. The thickness is measured in Dobson units, in this image, smaller amounts of overhead ozone are shown in blue, while larger amounts are shown in orange and yellow.
• The CERES instrument cover was opened on January 26, 2012. The "first light" process represented the transition from engineering checkout to science observations. The next morning CERES began taking Earth-viewing data, and on Jan. 29 scientists produced an image from the scans. 90)
Legend to Figure 59: The thick cloud cover tends to reflect a large amount of incoming solar energy back to space (blue/green/white image), but at the same time, reduce the amount of outgoing heat lost to space (red/blue/orange image). Contrast the areas that do not have cloud cover (darker colored regions) to get a sense for how much impact the clouds have on incoming and outgoing energy.
• The former NPP (NPOESS Preparatory Project) spacecraft has been renamed to Suomi NPP (National Polar-orbiting Partnership) on January 24, 2012 to honor the late Verner Suomi (1915-1995), a longtime UW (University of Wisconsin) -Madison professor and meteorologist (Ref. 1).
Suomi NPP is currently in its initial checkout phase before starting regular observations with all of its five instruments. The commissioning activities are expected to be completed by March 2012.
Legend to Figure 60: This composite image uses a number of swaths of the Earth's surface taken on January 4, 2012. The VIIRS instrument gets a complete daily view of Earth.
• The VIIRS instrument acquired its first visible range measurements on November 21, 2011 (Figure 62). To date, the images are preliminary, used to gage the health of the sensor as engineers continue to power it up for full operation.
Legend to Figure 61: Rising from the south and setting in the north on the daylight side of Earth, VIIRS images the surface in long wedges measuring 3,000 km across. The swaths from each successive orbit overlap one another, so that at the end of the day, the sensor has a complete view of the globe. The Arctic is missing because it is too dark to view in visible light during the winter.
Legend to Figure 63: This global image shows the ATMS channel 18 microwave antenna temperature at 183.3 GHz on November 8, 2011. This channel measures atmospheric water vapor; note that Tropical Storm Sean is visible in the data, as the blue patch, in the Atlantic off the coast of the Southeastern United States. The ATMS data were processed at the NOAA Satellite Operations Facility (NSOF)
Sensor complement: (ATMS, VIIRS, CrIS, OMPS, CERES)
The NPP instruments will demonstrate the utility of improved imaging and sounding data in short-term weather "nowcasting" and forecasting and in other oceanic and terrestrial applications, such as harmful algal blooms, volcanic ash, and wildfire detection. NPP will also extend the series of key measurements in support of long-term monitoring of climate change and of global biological productivity. 96)
Figure 64: Nadir deck view of the NPP spacecraft (image credit: NASA)
ATMS (Advanced Technology Microwave Sounder)
A NASA-provided new-generation instrument developed by NGES (Northrop Grumman Electronic Systems) in Azusa, CA as prime contractor (NGES is teamed with BAE Systems and Lockheed Martin). The objective is to combine the passive-microwave observation capabilities of three heritage instruments, namely AMSU-A1/A2 and AMSU-B/MHS, into a single instrument with a correspondingly reduced mass and power consumption and with advanced microwave-receiver electronics technologies. ATMS is a passive total power microwave sounder whose observations (measurement of microwave energy emitted and scattered by the atmosphere), when combined with observations from an infrared sounder (CrIS), provide daily global atmospheric temperature, moisture, and pressure profiles. ATMS observations are co-registered with those of CrIS. 97) 98) 99)
ATMS will replace instruments currently flying on the POES satellites. The new instrument is about one-third the size and mass of the existing microwave sounding instruments (on POES and on Aqua). This miniaturization of ATMS is enabled by the application of new technologies, principally in the area of microwave electronics. Also, this miniaturization enables the use of smaller spacecraft to fly ATMS and the other required instruments, thereby reducing the cost of future weather and climate research satellites.
ATMS is a cross-track scanning total power microwave radiometer, with a swath width of 2300 km and a spot size of approximately 1.5 km [the native observation resolution is finer than 1.5 km (in fact about 0.5 km), but ground processing performs a spatial averaging computation to increase the SNR]. Thus, the spatial resolution of the ATMS data products is 1.5 km.
The microwave emissions from the atmosphere entering the antenna apertures are reflected by a scanning, flat-plate reflector to a stationary parabolic reflector, which focuses the energy to a feed-horn. Behind the feedhorn, channels are frequency-diplexed into separate channels that are then amplified and fed though a bandpass filter to a detector.
The microwave detectors and associated electronics filter the microwave signal to measure 22 separate channels from 23 to 183 GHz, and convert the channels into electrical signals that are then digitized. Beginning with the front-end microwave optics, the 22 channels of the ATMS are divided into two groups: a low-frequency (23 to 57 GHz) group, and a high-frequency (88 to 183 GHz) group. The low frequency channels, 1 through 15, are primarily for temperature soundings and the high-frequency channels, 16 through 22, are primarily for humidity soundings (water vapor profiling).
Each group has an antenna aperture followed by a diplexing subsystem to further separate the channels. The input antenna elements are two flat reflectors joined together mechanically and driven by a single scan-drive motor with its associated control electronics. The single scanner design is necessary to realize the small sensor volume of approximately 40 cm x 60 cm x 70 cm.
The ATMS instrument data are transmitted to the spacecraft via a MIL-STD-1553B bus interface. ATMS has a mass of about 75 kg and consumes about 130 W of orbital average power. The ATMS science data rate is 20 kbit/s (average) and 28 kbit/s (max).
Table 7: Channel characteristics of ATMS
Instrument calibration: The instrument includes on-board calibration sources viewed by the reflectors during each scan cycle. The calibration of the ATMS is a so-called through-the-aperture type, two-point calibration subsystem. The warm reference point is a microwave blackbody target whose temperature is monitored. In addition, cold space is viewed during each scan cycle. Both calibrations provide for the highly accurate microwave sounding measurements required by the operational and science applications of ATMS data.
Table 8: Some performance parameters of ATMS
There are three antenna beamwidths. The temperature sounding channels are 2.2º (Nyquist-sampling in both along-scan & down-track directions) while the humidity channels are 1.1º. Channels 1 and 2 have a larger beam width of 5.2º. This is due to the limited volume available on the spacecraft for ATMS.
Figure 65: Functional block diagram of ATMS (image credit: NASA)
Figure 66: Schematic illustration of ATMS (image credit: NASA)
Figure 67: Elements of the ATMS design configuration (image credit: NASA)
Figure 68: Alternate view of ATMS (image credit: IPO)
On the ground, ATMS raw data are converted into brightness temperature measurements by channel, are radiometrically corrected using calibration data, and are ortho-rectified. ATMS brightness temperatures by channel are then used in conjunction with the corresponding data from the infrared sounder (CrIS) to retrieve atmospheric temperature and humidity profiles for use in data assimilation algorithms for operational or climate research use.
Data availability requirements:
• Make Raw Data Records (RDRs), Sensor Data Records (SDRs), and Environmental Data Records (EDRs) available within 180 minutes of observation, minimally 95% of the time over an annual basis
- RDR definition: Full resolution, digital sensor data, time-referenced and locatable in earth coordinates with absolute radiometric and geometric calibration coefficients appended, but not applied, to the data.
- SDR definition: Data record produced when an algorithm is used to convert Raw Data Records (RDRs) to geolocated, calibrated detected fluxes with associated ephemeris data. Calibration, ephemeris, and any other ancillary data necessary to convert the sensor units back to sensor raw data (counts) are included.
- EDR definition: Data records produced when an algorithm is used to convert SDRs to geophysical parameters (including ancillary parameters, e.g., cloud clear radiation, etc.).
• Make RDRs, SDRs, and EDRs available for at least 98% of all observations over an annual basis
• Provide a High Rate Direct-broadcast (HRD) link for in-situ users
• Store at least two and a half orbits of mission data on the satellite
Figure 69: Photo of the ATMS instrument (image credit: NASA) 100)
Data products: The NPP instrument data will be used to produce 29 of the 59 NPOESS EDRs. Of the 59 NPOESS EDRs six are considered key performance parameters. That is, the mission must as a minimum successfully generate those EDRs to be considered successful. NPP will generate data for all six of the key performance EDRs (Table 9).
Table 9: Key NPP EDRs
• Use of advanced low noise amplifier technology for atmospheric sounding (ATMS). Current microwave instruments split the arriving radiation into channels of frequencies, and then amplify them into electrical currents.
• S/C on-board processing using reconfigurable computing and RAM-based field-programmable gate arrays for generation of information products (option).
On-orbit ATMS instrument performance: Assessments of the on-orbit data from the Suomi NPP ATMS indicate all performance parameters are within expected values, confirming radiometric performance superior to AMSU. Furthermore, pitch-maneuver data has been used to develop a physical model for the scan-dependent bias effect, which has been a long-standing issue with cross-track scanning radiometers. Such a model can be used for developing a correction algorithm that could further reduce radiometric calibration errors relative to that of prior instruments. 101)
VIIRS (Visible/Infrared Imager and Radiometer Suite)
Raytheon Santa Barbara Remote Sensing (SBRS) is the prime contractor for this instrument to NGST. VIIRS is an advanced, modular, multi-channel imager and radiometer (of OLS, AVHRR/3, MODIS, and SeaWiFS heritage) with the objective to provide global observations (moderate spatial resolution) of land, ocean, and atmosphere parameters at high temporal resolution (daily). 102) 103) 104) 105) 106) 107) 108) 109)
VIIRS is a multispectral (22-band) opto-mechanical radiometer, employing a cross-track rotating telescope fore-optics design (operating on the whiskbroom scanner principle), to cover a wide swath. The rotating telescope assembly (RTA of 20 cm diameter) concept of SeaWiFS heritage allows a low straylight performance. An observation scene is imaged onto three focal planes, separating the VNIR, SWIR/MWIR, and TIR energy - covering a spectral range of 0.4 - 12.5 µm. The VNIR FPA (Focal Plane Array) has nine spectral bands, the SWIR/MWIR FPA has eight spectral bands, and the TIR FPA four spectral bands. The integral DNB (Day Night Band) capability provides a very large dynamic range low-light capability in all VIIRS orbits. The detector line arrays [16 detectors in each array for the SWIR/MWIR and TIR bands, 32 detectors in the array for the VNIR and DNB (Pan) bands] of the whiskbroom scanner are oriented in the along-track direction. This arrangement provides a parallel coverage of 11.87 km along-track in one scan sweep (cross-track direction). The wide along-track coverage permits sufficient integration time for all cells in each scan sweep. One cross-track scan period of RTA is 1.786 s in length. The data quantization is 12 bits (14 bit A/C converters for lower noise).
Typical data products (types) of VIIRS include atmospheric, clouds, earth radiation budget, clear-air land/water surfaces, sea surface temperature, ocean color, and low-light visible imagery. A swath width of 3000 km is provided (corresponding to FOV=±55.84º) with a spatial resolution for imagery related products of no worse than 0.4 km to 0.8 km (nadir to edge-of-scan). The radiometric bands provide a resolution about twice in size to the imagery bands. Note: Most derived data products will be produced at somewhat coarser resolutions by aggregation of on-board data.
Figure 70: General configuration of the VIIRS instrument (image credit: IPO)
The VIIRS instrument design employs an all-reflective optics assembly taking advantage of recent optics advances: a) single 4 mirror imager, b) 2 dichroics and 1 fold, c) aluminum DPT-bolt together technology (DPT = Diamond Point Turning). A rotating off-axis and afocal TMA (Three Mirror Anastigmatic) telescope assembly is employed [Note: The telescope rotates 360º, thus scanning the Earth scene, and then internal calibration targets.]. The aperture of the imaging optics is 19.1 cm in diameter, the focal length is 114 cm (f/5.97). The VIIRS optical train consists of the fore optics (TMA), the aft optics [an all-reflective FMA (Four Mirror Anastigmatic) imager], and the back-end optics, which include microlenses for the cooled focal planes.
A total of 22 spectral bands have been selected as defined in Table 10. VIIRS features band-to-band registration for all bands (optical alignment of all FPAs). A total of three focal planes and four FPAs (Focal Plane Arrays) cover the spectral range of the instrument, one FPA for DNB (Day-Night Band), one for VNIR, SWIR/MWIR, and TIR. The DNB spectral range of 0.5-0.9 µm CCD detector features four light-sensitive areas (3 with TDI, one without) and near-objective sample spacing.
Figure 71: Illustration of VIIRS instrument elements (image credit: Raytheon SBRS)
The VNIR FPA employs a PIN (Positive Insulator Negative) diode array/ROIC (Readout Integrated Circuit) design collocated with the DNB monolithic CCD. All detectors in the SWIR/MWIR/TIR regions employ photovoltaic (PV) detectors with an element spacing of 12 µm. A ROIC (Readout Integrated Circuit) at each FPA provides improved noise levels and built-in offset correction. A cryogenic module (three-stage radiative cooler) provides FPA cooling.
A single-board instrument computer provides a processing capability including data aggregation, data compression [lossless (2:1 Rice compression) and lossy (JPEG) algorithms are used], and CCSDS data formatting.
VIIRS calibration is performed with three on-board calibrators: a) a solar diffuser (SD) provides full aperture solar calibration, b) a solar diffuser stability monitor (SDSM) for the RSB (Reflective Solar Bands), and c) a BB (Blackbody)for the TEBs (Thermal Emissive Bands) calibration. Instrument calibration of VIIRS is based on that of the MODIS instrument: 110) 111) 112)
• VNIR: 1) View of a spectralon plate at the poles every few days; 2) Deep space view
• SWIR/MWIR/TIR: 1) View of blackbody every scan; 2) Deep space view
As a result of the MODIS-based calibration methods, VIIRS also carries out a series of MODIS-like on-orbit calibration activities, which include regularlyscheduled lunar observations and periodical BB warmup and cool-down (WUCD) operations. A number of MODIS event scheduling and data analysis tools have also been modified for VIIRS applications. Both BB and space view (SV) observations are made on a scanby-scan basis. VIIRS SD calibration is performed every orbit over the South Pole. Currently (2013) the SDSM, designed to track SD on-orbit degradation, is operated on a daily basis. Similar to MODIS operation, the VIIRS BB is nominally controlled at a constant temperature (292.5 K). On a quarterly basis, the BB performs a WUCD operation, during which its temperatures vary from instrument ambient to 315 K. 113)
VIIRS calibration validation: The VIIRS on-orbit calibration performance has been continuously assessed using data collected from its on-board calibrators and from the scheduled lunar observations. The yaw maneuvers have provided valuable data to update the prelaunch LUTs (Look-up Tables), generating new values for the SD bi-directional reflectance factor (BRF) and SD attenuation screen (SAS) transmission product, and SDSM Sun view screen transmission. A pitch maneuver was executed to validate the TEB response versus scan-angle (RVS). The BB WUCD operations scheduled on a quarterly basis have shown an excellent TEB detector nonlinearity and NEdT performance over a wide range of temperatures.
The NASA VCST (VIIRS Characterization Support Team) has provided independent evaluation of the VIIRS calibration and SDR product quality, and has met its design requirements of making recommendations for SDR operational code improvements and calibration coefficients LUT updates. The VCST will continue to support operational processing system to improve radiometric quality and investigate uncertainty assessment and new methodologies for VIIRS SDR improvements (Ref. 113).
Figure 72: Major subsystems/components of VIIRS (functional block diagram)
The NPP Instrument Calibration Support Element (NICSE) is one of the elements within the NASA NPP Science Data Segment (SDS). The primary responsibility of NICSE is to independently monitor and evaluate on-orbit radiometric and geometric performance of the VIIRS instrument and to validate its SDR (Sensor Data Record).
The NICSE interacts and works closely with other SDS Product Evaluation and Analysis Tools Elements (PEATE) and the NPP Science Team (ST) and supports their on-orbit data product calibration and validation efforts. The NICSE also works closely with the NPP Instrument Calibration Support Team (NICST) during sensor pre-launch testing in ambient and thermal vacuum environment. 114)
Figure 73: Schematic of VIIRS rotating TMA (Three Mirror Anastigmatic) telescope assembly
The VIIRS instrument has a mass of 275 kg, power of ~ 200 W (operational average), and a size of 134 cm x 141 cm x 85 cm. The data rate is 10.5 Mbit/s (high rate mode) and 8 Mbit/s (average rate) mode with 10:1 JPEG compression). The VIIRS instrument features a SBC (Single Board Computer) for all instrument operations and control; it communicates with the S/C via an IEEE 1394a cable interface.
Some operational features of VIIRS:
• All functions are individually commandable
• Macro commands (stored sequences, all macros are reprogrammable) simplify the commanding and reduce the uplink data
• Time-tagged commands allow delayed execution (provides for 30 days autonomous operations)
• The swath widths and locations are individually programmable by band (improved resolution views of selected target near nadir)
• Diagnostic mode features improved versatility
Table 10: Definition of VIIRS spectral bands
Table 11: Overview of the FPA design of VIIRS
Some key EDRs of VIIRS: 115)
• SST (Sea Surface Temperature). VIIRS is capable to provide a nadir resolution of 750 m (by aggregating detectors 3:l in-track near nadir, 2:l in-track aggregation out to a 2,000 swath, and 1:1 out to 3,000 km) to simultaneously optimize spatial resolution and noise performance. - The SST solution combines the traditional long-wave infrared (LWIR) split window with a second split window in the mid-wave infrared (MWIR) for a globally robust SST algorithm. The MWIR split window has a higher transmissivity than the traditional LWIR split window for improved atmospheric correction. The low-noise design is operable day and night with 0.25 K precision, and 0.35 K total measurement uncertainty (rms error).
• Imagery and cloud detection/typing. The imagery solution provided on VIIRS includes six high-resolution bands and an additional 16 moderate-resolution bands. One of these, a reflective panchromatic band (DNB), is operable in low-light conditions down to a quarter moon. A swath with of 3000 km is provided.
• Soil moisture. A VIIRS/CMIS data fusion solution was derived. The approach combines the fine spatial resolution of VIIRS with traditional coarser-resolution microwave-derived soil moisture retrievals to achieve excellent results over both open and partially vegetated scenes. The estimation procedure involves two steps: 1) CMIS estimates soil moisture at coarse spatial resolution. This involves inversion of dual-polarized microwave brightness temperatures. 2) CMIS-derived low-resolution soil moisture is linked to the scene optical parameters, such as NDVI (Normalized Difference Vegetation Index), surface albedo, and LST (Land Surface Temperature). The linkage of the microwave-derived soil moisture to NDVI, surface albedo and LST is based on the "Universal Triangle" approach of relating land surface parameters. The three high-resolution optical parameters are aggregated to microwave resolution for the purpose of building the linkage model. The linkage model, in conjunction with high-resolution NDVI, surface albedo, and LST, is then used to disaggregate microwave soil moisture into high-resolution soil moisture.
VIIRS will collect radiometric and imagery data in 22 spectral bands within the visible and infrared region ranging from 0.4 to 12.5 µm. These data are calibrated and geolocated in ground processing to generate Sensor Data Records (SDRs) that are equivalent to NASA Level 1B products. The VIIRS SDRs in turn will be used to generate 22 EDRs (Environmental Data Records) including two KPPs (Key Performance Parameters): SST (Sea Surface Temperature) and Imagery. Since the quality of these EDRs depends upon the quality of the underlying SDRs, adequate SDR quality is crucial to NPP mission success. 116)
Figure 74: Photo of the VIIRS instrument (image credit: NASA, Raytheon) 117)
DNB (Day Night Band) overview in VIIRS:
The DNB will measure VIS radiances from the Earth and atmosphere (solar/lunar reflection and both natural and anthropogenic nighttime light emissions) during both day and night portions of the orbit. In comparison to the OLS (Operational Linescan System) of the DMSP series, some of the DNB channel improvements include 1) reduced instances of pixel saturation, 2) a smaller IFOV, leading to reduced spatial blurring, 3) superior calibration and radiometric resolution, 4) collocation with multispectral measurements on VIIRS and other NPOESS sensors, 5) and generally increased spatial resolution and elimination of cross-track pixel size variation. 118)
The DNB is implemented as a dedicated focal plane assembly (FPA) that shares the optics and scan mechanism of the other VIIRS spectral bands. This integral design approach offers lower overall system complexity, cost, mass, and volume compared to a separate DNB sensor. Unlike the OLS, the DNB will feature radiometric calibration, with accuracy comparable to the other VIIRS spectral bands.
To achieve satisfactory radiometric resolution across the large dynamic range (seven orders of magnitude) of day/night radiances encountered over a single orbit, the DNB selects its amplification gain dynamically from three simultaneously collecting stages (groups of detectors residing upon the same FPA). The stages detect low-, medium-, and high-radiance scenes with relative radiometric gains of 119,000:477:1 (high:medium:low gain). Each of the three stages covers a radiance range of more than 500:1, so that the three together cover the entire required radiance range with generous overlap. Two identical copies of the high-gain stage are provided, which improves the SNR at very low signal levels and allows for the correction of pixels impacted by high-energy subatomic particles. The scene is scanned sequentially such that each scene is imaged by all three gains virtually simultaneously.
The signals from all gain stages are always digitized, using 14 bits for the high-gain stage and 13 bits for the medium- and low-gain stages. This fine digitization assures the DNB will have a sufficiently fine radiometric resolution across the entire dynamic range. Logic in the VIIRS Electronics Module (EM) then selects, on a pixel-by-pixel basis, the most appropriate of the three stages to be transmitted to Earth. In general, the VIIRS EM logic chooses the most sensitive stage in which the pixel is not saturated. This imaging strategy produces nonsaturated calibrated radiances in bright areas, and data with a lower dynamic range in the darkest areas with less SNR and radiometric accuracy.
In summary, the VIIRS DNB feature will bring significant advances to operational and research applications at night (over OLS operations) due to the increased sensitivity of the instrument.
VIIRS features 15 reflective solar bands (RSB) in the range of 0.4-2.25 µm. The reflective bands use sunlight reflected from a SD (Solar Diffuser) after passing through an attenuating SDS (Solar Diffuser Screen) as a reference illumination source. The RSB calibration is currently performed by offline trending of calibration scale factors derived from the SD and SV (Space View) observations. These calibration scale factors are used to periodically update LUT (Look-Up Tables) used by the ground processing to generate the calibrated earth radiance and reflectance in the Sensor Data Records (SDR).
RSB calibration data is acquired once per orbit when sunlight incident on the SD uniformly illuminates the VIIRS detectors, providing a large and calculable reference radiance level. The calibration scale factor is the ratio of the calculated SD radiance at the RTA entrance aperture to the SD radiance measured by the instrument using calibration coefficients derived from the pre-launch calibration. The calibration scale factor in effect measures the change in instrument "gain" as the instrument ages on orbit relative to the gain measured during pre-launch instrument response characterization.
TED (Thermal Emissive Band) calibration: 121)
VIIRS has 7 thermal emissive bands use an OBC-BB (On-Board Calibrator Blackbody) maintained at a constant elevated temperature as a reference illumination source. The 7 emissive bands are centered at 3.74, 11.45, 3.75, 4.05, 8.55, 10.76, and 12.01 µm. The two emissive image bands are mainly for cloud imagery and precise geolocation. The 5 moderate-resolution emissive bands are used to determine surface temperature and cloud top pressure. The only dual gain band TEB M13 is used for determining surface temperature at low radiance, and fire detection at high radiance.
The VIIRS emissive band calibration concept is a common two-point calibration by viewing onboard blackbody and cold space. However, the VIIRS emissive band calibration algorithm is more complicated than other sensors such as AVHRR and MODIS, because of the instrument response verses the scan angle. The TEBs (Thermal Emissive Bands) are calibrated using OBC-BB that has been carefully characterized in prelaunch activities. The OBC-BB emissivity is estimated to be 0.99609-0.99763 for the TEB bands based on prelaunch testing in the thermal vacuum chamber. The OBC-BB temperature is carefully controlled using heater elements and thermistors. The calibration algorithm, based on measured BB temperature and emissivity, computes radiances and compares it with counts to determine gain adjustments.
VIIRS significantly outperforms the legacy AVHRR in spatial, spectral, and radiometric accuracy. Early assessment of the VIIRS TEB calibration shows the sensor is stable and exceeds the specification. The onboard calibration accuracy for NEdT compares very favorably with pre-launch thermal vacuum tests. Consistency tests among VIIRS, MODIS, AVHRR, and CrIS further confirm the stability and accuracy of the VIIRS TEB.
CrIS (Cross-Track Infrared Sounder)
The FTS (Fourier Transform Spectrometer) instrument is being developed by Exilis (former ITT Aerospace/Communications Division) of Ft. Wayne, IN, as the prime contractor. CrIS, of HIRS/4 (POES) and AIRS (Aqua) heritage, is a high-spectral and high-spatial resolution infrared sounder for atmospheric profiling applications. The overall objective is to perform daily measurements of Earth's upwelling infrared radiation to determine the vertical atmospheric distribution (surface to the top of the atmosphere) of temperature (profiles to better than 0.9 K accuracy in the lower troposphere and lesser accuracy at higher altitudes), moisture (profiles to better than 20-35% accuracy depending on altitude) and pressure (profiles to better than 1.0% accuracy ) with an associated 1.0 km vertical layer resolution. The Michelson interferometer sounder has over 1300 spectral channels, it covers a spectral range of 650-2550 cm-1 (or 3.9 to 15.4 µm), with a spectral resolution of 0.6525 cm-1 (LWIR), and a ground spatial resolution (IFOV) of 14.0 km. The IFOVs are arranged in a 3 x 3 array. The swath width is 2300 km (FOV of ±48.33º). 122)
Figure 75: Illustration of the CrIS instrument (image credit: ITT, IPO)
The "unapodized spectral resolution" requirement is defined as I/(2L), where L is the maximum optical path difference from ZOND (Zero Path Difference) to MPD (Maximum optical Path Difference). The on-axis unapodized spectral resolution for each spectral band shall be ≤to the values given in Table 12. Since L determines the unapodized spectral resolution, the nominal value for L is also given in the table. 123)
Table 12: Spectral requirements of the CrIS instrument
The flight configuration for the CrIS DPM (Detector Preamplifier Module) consists of three spectrally separate (SWIR, MWIR and LWIR) FPAAs (Focal Plane Array Assemblies), three (SWIR, MWIR and LWIR) signal flex cable assemblies, a warm signal flex cable/vacuum bulk head assembly, and the DPM warm electronics CCAs (Circuit Card Assemblies). The FPAAs are cooled to cryogenic temperature (98 K SWIR, MWIR, 81 K for LWIR) by the detector cooler module. The cryogenic portions of the DPM (FPAAs, and signal flex cable assemblies) mate to the ambient temperature portions of the DPM (warm signal flex cable assembly and the ambient temperature portions of the transimpedance amplifier, mounted within the CCAs) through the vacuum bulk head assembly mounted on the detector cooler assembly housing. 124)
The baseline CrIS instrument design consists of nine independent single-function modules: [telescope, optical bench, aft-optics, interferometer (FTS), ICT (Independent Calibration Target), SSM (Scene Selection Module), detectors, cooler, processing and control electronics, and instrument structure]. 125)
• 8 cm clear aperture
• A collimator is used to perform the spatial and spectral characterizations
• 4-stage split-patch passive cooler (81 K for LWIR patch temperature, 98 K for MWIR/SWIR patch)
• High-performance PV (photovoltaic) detectors
• 3 x 3 arrays (14 km IFOVs)
• Three spectral bands (SWIR, MWIR, TIR), co-registered so that the FOVs of each band see the radiance from the same region of the Earth's atmosphere
• All-reflective telescope
• Proven Bomem plane-mirror Michelson interferometer with dynamic alignment
• Deep-cavity internal calibration target based on MOPITT design
• Two-axis scene selection module with image motion compensation
• A modular design (allowing for future addition of an active cooler and >3 x 3 arrays
Table 13: Key performance characteristics of CrIS
The primary data product of the CrIS instrument are interferograms collected from 27 infrared detectors that cover 3 IR bands and 9 FOVs. 126)
Data of CrIS will be combined in particular with those of ATMS to construct atmospheric temperature profiles at 1 K accuracy for 1 km layers in the troposphere and moisture profiles accurate to 15% for 2 km layers. 127)
Figure 76: Illustration of the CrIS instrument (image credit: IPO)
Figure 77: Photo of the CrIS instrument (image credit: Exelis)
CrIS + ATMS = CrIMSS (Cross-track Infrared Microwave Sounding Suite)
CrIS is designed to work in unison with ATMS (Advanced Technology Microwave Sounder); together they create CrIMSS (Cross-track Infrared Microwave Sounding Suite). The objective of CrIMSS is to provide global 3D soundings of atmospheric temperature, moisture and pressure profiles. In addition, CrIMSS has the potential to provide other surface and atmospheric science data, including total ozone and sea surface temperature. ATMS provides high spatial resolution microwave data to support temperature and humidity sounding generation in cloud covered conditions. Note: See ATMS description under NPP.
Table 14: CrIMSS mission products (EDRs)
Figure 78: The basic observation scheme of CrIMSS to construct vertical profiles of temperature, moisture & pressure EDRs for NPOESS (image credit: IPO)
Post-launch evaluation of CrIMSS EDRs: 128)
As a part of post-launch validation activities, CrIS/ATMS SDRs generated for February 24, 2012 were used to produce CrIMSS-EDR products. Aqua-AIRS/AMSU SDRs acquired for this day were processed to generate AST heritage algorithm (version 5.9) products. Both these EDR products were evaluated with matched ECMWF analysis fields and RAOB measurements.
The CrIS and ATMS instruments aboard the Suomi NPP satellite provide high quality hyper-spectral Infrared (IR) and Microwave (MW) observations to retrieve atmospheric vertical temperature, moisture, and pressure profiles (AVTP, AVMP and AVPP), and many other EDRs (Environmental Data Records). The CrIS instrument is a Fourier Transform Spectrometer (FTS) instrument with a total of 1305 IR sounding channels. The instrument is similar to other hyper-spectral IR sounding instruments, namely, the IASI (Infrared Atmospheric Sounding Interferometer) aboard MetOp (Meteorological Operational satellite program), and the AIRS (Atmospheric Infrared Sounder) aboard the Aqua satellite. All these hyper-spectral IR sounders are accompanied by MW sounding instruments to assist in the generation of high quality geophysical products in scenes with up to 80% cloud-cover. The IASI instrument is accompanied by the 15-channel AMSU-A (Advanced Microwave Sounding Unit) and the 5-channel MHS (Microwave Humidity Sounder). The Aqua-AIRS is accompanied by the AMSU-A instrument. The ATMS instrument that accompanied the CrIS has a combination of channels similar to that of AMSU-A and MHS. Details of these instruments and their channel characteristics are described in many publications.
Figure 79: Post-launch evaluation of CrIMSS OPS-EDR Product with Aqua-AIRS/AMSU heritage algorithm retrievals and ECMWF analysis fields (image credit: NOAA, NASA)
Legend to Figure 79: Global 850-hPa temperature retrieval for 02/24/2012: (a) CrIMSS second stage ‘IR+MW' retrieval; (b) ATMS-only retrieval; (c) Corresponding ECMWF analysis; (d) Aqua-AIRS retrieval; (e) Aqua-AMSU retrieval; (f) corresponding ECMWF analysis. The CrIMSS OPS-EDR product depicts patterns reasonably well, and difference maps generated (retrieval vs. truth, not shown) also shows reasonable promise with the AIRS heritage algorithm results.
The AVTP (Atmospheric Vertical Temperature Profile) and AVMP (Atmospheric Vertical Moisture Profile) retrievals produced by the Cross-track Infrared Sounder and the Advanced Technology Microwave Sounder suite (CrIMSS) official algorithm were evaluated with global ECMWF (European Center for Medium Range Weather Forecast) analysis fields, radiosonde (RAOB) measurements, and AIRS (Aqua-Atmospheric Infrared Sounder) heritage algorithm retrievals.
The operational CrIMSS AVTP and AVMP product statistics with truth data sets are quite comparable to the AIRS heritage algorithm statistics. Planned updates and improvements to the CrIMSS algorithm will alleviate many issues observed with ‘day-one' focus-day results and show promise in meeting the Key Performance Parameter (KPP) specifications.
OMPS (Ozone Mapping and Profiler Suite):
OMPS is a limb- and nadir-viewing UV hyperspectral imaging spectrometer, designed and developed at BATC (Ball Aerospace & Technologies Corp.), Boulder, CO. The objective is to measure the total amount of ozone in the atmosphere and the ozone concentration variation with altitude. OMPS is of SBUV/2, TOMS and GOME heritage. Also, the OMPS limb-sounding concept/technology was already tested with ISIR (Infrared Spectral Imaging Radiometer) flown on Shuttle flight STS-85 (Aug. 7-19, 1997) and with SOLSE/LORE flown on STS-87 (Nov 19 - Dec. 5, 1997). The vertical resolution requirement demands an instrument design to include a limb-viewing sensor in addition to a heritage-based nadir-viewing sensor. 129) 130) 131)
Table 15: Overall mission requirements for OMPS ozone observations 132)
The OMPS instrument design features two coregistered spectrometers in the OMPS nadir sensor and a limb sensor, measuring the limb scatter in the UV, VIS, and NIR. The instrument has a total mass of 56 kg, an average power consumption of 85 W, a size of 0.35 m x 0.54 m x 0.56 m, and a data rate of 165 kbit/s.
Figure 80: Schematic view of the OMPS instrument (image credit: IPO)
1) Nadir-viewing instrument:
The nadir sensor wide-field telescope feeds two separate spectrometers, a) for total column observations (mapper) and b) for nadir profiling observations. The total column spectrometer (300-380 nm spectral range, resolution of 0.42 nm) has a 2800 km cross-track swath (FOV = 110º and an along-track slit width of 0.27º) divided into 35 IFOVs of nearly equal angular extent. The CCD pixel measurements from its cross-track spatial dimension are summed into 35 bins. The summed bins subtend 3.35º (50 km) at nadir and 2.84º at ±55º. The along-track resolution is 50 km at nadir due to spacecraft motion during the 7.6 second reporting period. Measurements from this spectrometer are used to generate total column ozone data with a resolution of about 50 km x 50 km at nadir.
The nadir profile spectrometer (250-310 nm) has a 250 km cross-track swath corresponding to a single cell (cross-track FOV = 16.6º, and 0.26º along-track slit width). Co-registration with the total column spectrometer provides the total ozone, surface and cloud cover information needed for nadir profile retrievals. All of the cross-track pixels are binned spatially to form a single cell of 250 km x 250 km. Some instrument parameters are: 133)
- The telescope is a three mirror, near telecentric, off-axis design. The FOV is allowed to curve backward (concave in the anti-ram direction) by 8.5º at 55º cross-track in order to maintain straight entrance slits for the spectrometers. The mirrors are made with a glass which matches the thermal expansion of Titanium, are coated with an enhanced aluminum, and have an rms surface roughness of < 15Å.
- Each of the 2 spectrometers has a CCD detector array, a split column frame transfer CCD 340 x 740 (column x row) operated in a backside illuminated configuration. The pixel pitch is 20 µm in the column (spectral) dimension and 25 µm in the row (spatial) dimension and every pixel in both the active and storage regions contains a lateral overflow antiblooming structure integrated into a 4-phase CCD architecture.
- Both spectrometers sample the spectrum at 0.42 nm, 1 nm FWHM end-to-end resolution
- Electronics: a) CCD preamplifier electronics in sensor housing, b) main electronics box performs A/D conversion and on-orbit pixel correction
- The OMPS nadir instrument has a mass of 12.5 kg and a size of 31 cm x 32 cm x 20 cm.
Polarization compensators are used to reduce polarization sensitivity for both Nadir instruments. Long-term calibration stability is monitored and corrected by periodic solar observations using a "Working" and "Reference" reflective diffuser system (similar to that successfully deployed on the TOMS sensors).
Figure 81: The nadir-viewing OMPS instrument (image credit: BATC)
2) Limb profiler:
The limb profiler consists of the following major elements: telescope, the spectrometer, and the calibration & housing mechanism. It uses a single prism to disperse three vertical slits directed along-track, each separated by 250 km at the limb tangent point (one slit views in the orbital plane and the other two slits view to either side of the orbital plane). The vertical slits are separated by 4.25° across track corresponding to 250 km at the tangent points. Each slit has a vertical FOV of 1.95° corresponding to 112 km at the limb to cover altitudes from 0 to 60 km in the atmosphere and also allow for pointing errors, orbital variation, and the Earth's oblateness. Individual pixels on the CCD are spaced every 1.1 km of vertical image and have a vertical resolution of 2.2 km. The instrument uses prism spectrometers to cover the spectral range from 290 nm to 1000 nm.
To accommodate the very high scene dynamic range, these slit images pass through a beam splitter to divide the scene brightness into three brightness ranges. As a result there are nine limb images of the dispersed slits on the CCD. The measured limb radiances in the ultraviolet, visible, and near-infrared provide data on ozone, aerosols, Rayleigh scattering, surface and clouds that are used to retrieve ozone profiles from the tropopause to 60 km. 134)
Some limb sensor parameters: The sensor consists of a telescope with three separate cross-track fields of view of the limb, a prism spectrometer covering 290 to 1000 nm, and a solar-diffuser calibration mechanism. The sensor provides 2.2 km vertical resolution profiles of atmospheric radiance with channel spectral resolutions (FWHM) ranging from 0.75 nm at 290 nm to 25 nm at 1000 nm and handles the demanding spectral and spatial dynamic range (4-5 orders in magnitude variation) of the limb-scattered solar radiation with the required sensitivity for ozone retrievals (polarization compensators are also used). The large scene dynamic range is accommodated by using two separate apertures in each telescope, producing two optical gains, and by using two integration times, producing two electronic gains. All six spectra (resulting from three slits viewed through two apertures) are captured on a single CCD FPA. The window above the detector is coated with filters for the ultraviolet and visible regions of the spectra to reduce stray light. The limb sensor has a 38 second reporting period (corresponding to 250 km along-track motion) that includes multiple interspersed exposures at long and short integration times.
Limb-viewing measurements of scattered UV sunlight can be registered in altitude if the altitude errors correspond to a rigid vertical shift, if the instrument measures radiances dominated by single Rayleigh scattering at altitudes where good temperature and pressure data are available from another source. 135)
Figure 82: OMPS limb sensor mechanical layout
The staring spectrometer architecture and hyperspectral coverage eliminate the need for any continuous-action mechanisms, increasing the reliability of the sensor.
OMPS calibration: Solar illuminated diffusers are used for radiometric and spectral calibrations (two diffusers for each sensor). The working diffuser is used weekly and the reference diffuser is used twice annually to monitor the on-orbit degradation of the working diffuser.
Table 16: Performance parameters of the OMPS spectrometers
In March 2009, BATC had completed integration and risk reduction testing of OMPS PFM (Proto Flight Model) for NPP. 136)
The OMPS program will create five ozone data EDR products:
• Total ozone column: High performance total column environmental data record
• Nadir ozone profile: Heritage SBUV/2 nadir profile data records
• Limb ozone profile: High performance ozone profile product
• Infrared total ozone: data records from CrIS (Cross-track Infrared Sounder) radiances.
• Calibrated radiances: Heritage TOMS V7 total column data records
Secondary OMPS products are: SO2 index, aerosols (index and profile), UV-B radiance on Earth's surface, NO2, surface albedo, and cloud top height.
CERES (Clouds and the Earth's Radiant Energy System):
CERES is a NASA/LaRC instrument built by Northrop Grumman (formerly TRW Space and Technology Group) of Redondo Beach, CA (PI: Bruce Wielicki). The CERES instrument measures the reflected shortwave (SW) and Earth emitted radiances. The objectives are to continue a consistent database of accurately known fields of Earth's reflected solar and Earth's emitted thermal radiation. CERES satisfies four NPOESS EDRs, in combination with other instruments: 137) 138) 139) 140) 141) 142)
- Net solar radiation at TOA (Top of the Atmosphere)
- Downward longwave radiation at the surface
- Downward shortwave radiation at the surface
- Outgoing longwave radiation at TOA.
The CERES EDRs are essential to understanding Earth weather & climate.
- Measurement of clear sky fluxes aids in monitoring climate forcing and feedback mechanisms involving surface radiative characteristics
- These data are fundamental inputs to atmospheric and oceanic energetics
- They provide a basic input to extended range (10 day or longer) weather forecasting
- They provide a measure of the effect of clouds on the energy balance, one of the largest sources of uncertainty in climate modeling.
The legacy to CERES builds on the highly successful ERBE (Earth Radiation Budget Experiment) scanners flown on NOAA spacecraft. In addition CERES instruments are flown on the TRMM, Terra and Aqua missions of NASA. The CERES FM-5 (Flight Model 5) is being used on Suomi NPP.
The CERES instrument consists of three major subassemblies: 1) Cassegrain telescope, 2) baffle for stray light, and 3) detector assembly, consisting of an active and compensating element. Radiation enters the unit through the baffle, passes through the telescope and is imaged onto the IR detector. Uncooled infrared detection is employed.
Figure 83: Cross section of the CERES telescope (image credit: NASA/LaRC) 143)
A CERES instrument consists of 2 identical scanners: total mass of 114 kg , power = 100 W (average, 2 instruments), data rate = 20 kbit/s, duty cycle = 100%, thermal control by heaters and radiators, pointing knowledge = 180 arcsec. The design life is six years. CERES measures longwave (LW) and shortwave (SW) infrared radiation using thermistor bolometers to determine the Earth's radiation budget. There are three spectral channels in each radiometer:
- VNIR+SWIR: 0.3 - 5.0 µm (also referred to as SW channel); measurement of reflected sunlight to an accuracy of 1%.
- Atmospheric window: 8.0 - 12.0 µm (also referred to as LW channel); measurement of Earth-emitted radiation, this includes coverage of water vapor
-Total channel radiance in the spectral range of 0.35 - 125 µm;. reflected or emitted infrared radiation of the Earth-atmosphere system, measurement accuracy of 0.3%.
Limb-to-limb scanning with a nadir IFOV (Instantaneous Field of View) of 14 mrad, FOV = ±78º cross-track, 360º azimuth. Spatial resolution = 10-20 km at nadir. Each channel consists of a precision thermistor-bolometer detector located in a Cassegrain telescope.
Instrument calibration: CERES is a very precisely calibrated radiometer. The instrument is measuring emitted and reflected radiative energy from the surface of the Earth and the atmosphere. A variety of independent methods are used to verify calibration: 144)
• Internal calibration sources (blackbody, lamps)
• MAM (Mirror Attenuator Mosaic) solar diffuser plate. MAM is used to define in-orbit shifts or drifts in the sensor responses. The shortwave and total sensors are calibrated using the solar radiances reflected from the MAM's. Each MAM consists of baffle-solar diffuser plate systems, which guide incoming solar radiances into the instrument FOV of the shortwave and total sensor units.
• 3-channel deep convective cloud test
- Use night-time 8-12 µm window to predict longwave radiation (LW): cloud < 205K
- Total - SW = LW vs Window predicted LW in daytime for same clouds <205K temperatures
• 3-channel day/night tropical ocean test
• Instrument calibration:
- Rotate scan plane to align scanning instruments TRMM, Terra during orbital crossings (Haeffelin: reached 0.1% LW, window, 0.5% SW 95% configuration in 6 weeks of orbital crossings of Terra and TRMM)
- FM-1 and FM-2 instruments on Terra at nadir
Table 17: CERES instrument parameters
Figure 84: NPP CERES data system architecture (image credit: NASA/LaRC)
Figure 85: Photo of the CERES flight modules in 1999 (image credit: NASA)
Figure 86: Illustration of the CERES instrument (image credit: NASA/LaRC)
Figure 87: Engineers inspect the CERES FM-25 sensor following the completion of thermal vacuum testing at NGC (image credit: NGC) 145)
Table 18: CBERS instruments on NASA missions
Ground Segment of Suomi NPP:
The NPP ground segment will consist of the following elements:
• C3S (Command Control & Communication Segment), IPO responsibility. The C3S will be responsible for the operations of the NPP satellite. It will also provide the data network to route the mission data to the ground elements and the ground receive stations to communication with the NPP satellite. As part of the NPP operations, the C3S will provide the overall mission management and coordination of joint program operations.
• IDPS (Interface Data Processing Segment), IPO responsibility. The IDPS will ingest the raw sensor data and telemetry received from the C3S. It will process RDRs (Raw Data Records), SDRs (Sensor Data Records), and EDRs (Environmental Data Records). RDRs are defined as full resolution uncalibrated raw data records. SDRs are full resolution geo-located and calibrated sensor data. EDRs are fully processed data containing environmental parameters or imagery. The RDRs, SDRs, and EDRs will be made available to the four US Operational Processing Centers (OPCs) for processing and distribution to end users. The US OPCs consist of the following entities:
- NOAA/NESDIS serves as NCEP (National Centers for Environmental Prediction)
- AFWA (Air Force Weather Agency)
- FNMOC (Fleet Numerical Meteorology and Oceanographic Center)
- Naval Oceanographic Office (NavOceano)
• ADS (Archive & Distribution Segment). NOAA is responsible for providing ADS.
• SDS (Science Data Segment). NASA responsibility.
• PEATE (Product Evaluation and Algorithm Test Element)
Figure 89: Suomi NPP mission system architecture (NASA, NOAA)
Figure 90: SDS (Science Data System) architecture (image credit: NASA) 147)
NOAA's CLASS (Comprehensive Large Array-data Stewardship System) serves as the official repository of Suomi NPP mission data, including VIIRS. On line search, order, and distribution of all archived VIIRS mission data (along with tutorials) is available through CLASS. 148) 149)
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The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (email@example.com).