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
Figure 9: High definition video of 'Earth From Space at Night' from the VIIRS instrument of the NASA/NOAA Suomi NPP Satellite (video credit: CoconutScienceLab, Published on Dec 10, 2012)
Note: As of January 2020, the previously single large SuomiNPP file has been split into two files, to make the file handling manageable for all parties concerned, in particular for the user community.
• This article covers the SuomiNPP mission and its imagery in the period 2020 and 2019
• January 14, 2020: In January 2020, the Taal Volcano awoke from 43 years of quiet and spewed lava and ash, filling streets and skies of the Philippine island of Luzon with fine ash fall and volcanic gases. The eruption caused tens of thousands of people to evacuate their homes and forced the closure of several key roads, businesses, and an airport. 26)
- The volcano first unleashed a steam-driven explosion (known as a phreatic eruption) on January 12. In the early morning of January 13, eruptive activity increased and the volcano emitted a fountain of lava for about an hour and a half. According to the Philippine Seismic Network, 144 volcanic earthquakes have been recorded since January 12, suggesting continuous magmatic activity underneath Taal and potentially more eruptive activity.
- According to news reports, the eruption of Taal lofted ash up to 14 km (9 miles) into the air. The eruption was accompanied by intense thunder and lightning above the summit. Winds carried volcanic ash north across Luzon.
Figure 10: The time-series animation above shows the growth and spread of the volcanic plume from January 12-13, as observed by Japan’s Himawari-8 satellite (image credit: JMA (Japan Meteorological Agency), Story by Kasha Patel)
Figure 11: This map shows stratospheric sulfur dioxide concentrations on January 13, 2020, as detected by the Ozone Mapping Profiler Suite (OMPS) on the NOAA-NASA Suomi-NPP satellite [image credit: NASA Earth Observatory, image by Lauren Dauphin, using OMPS data from the Goddard Earth Sciences Data and Information Services Center (GES DISC). Story by Kasha Patel]
- Taal is the second-most active volcano near Manila, which is located approximately 60 kilometers (40 miles) north of the volcano. In total, ten cities and municipalities surround Taal. The Philippine Institute of Volcanology and Seismology (PHIVOLCS) has ordered a “total evacuation” for people in high-risk areas within a 14-kilometer radius from the main crater, affecting around half a million people.
• January 9, 2020: The fires in Australia are not just causing devastation locally. The unprecedented conditions that include searing heat combined with historic dryness, have led to the formation of an unusually large number of pyrocumulonimbus (pyroCbs) events. PyroCbs are essentially fire-induced thunderstorms. They are triggered by the uplift of ash, smoke, and burning material via super-heated updrafts. As these materials cool, clouds are formed that behave like traditional thunderstorms but without the accompanying precipitation. 27)
Figure 12: The VIIRS RGB imagery provides a “true-color” view of the smoke. (Note that these images do not represent what a human would see from orbit. In these images, the effect of Rayleigh scattering, which would add “blue haze,” has been taken out.) While useful, it is often hard to distinguish smoke over clouds and, sometimes, over dark ocean surfaces (image credit: NASA, Colin Seftor)
- PyroCb events provide a pathway for smoke to reach the stratosphere more than16 km in altitude. Once in the stratosphere, the smoke can travel thousands of miles from its source, affecting atmospheric conditions globally. The effects of those events — whether the smoke provides a net atmospheric cooling or warming, what happens to underlying clouds, etc.) — is currently the subject of intense study.
- NASA is tracking the movement of smoke from the Australian fires lofted, via pyroCbs events, more than 15 km high. The smoke is having a dramatic impact on New Zealand, causing severe air quality issues across the county and visibly darkening mountaintop snow.
- Two instruments aboard NASA-NOAA’s SuomiNPP satellite — VIIRS and OMPS-NM — provide unique information to characterize and track this smoke cloud. The VIIRS instruments provided a “true-color” view of the smoke with visible imagery. The OMPS series of instruments comprise the next generation of back-scattered UltraViolet (BUV) radiation sensors. OMPS-NM provides unique detection capabilities in cloudy conditions (very common in the South Pacific) that VIIRS does not, so together both instruments track the event globally.
Figure 13: The UV aerosol index is a qualitative product that can easily detect smoke (and dust) over all types of land surfaces. It also has characteristic that is particularly well suited for identifying and tracking smoke from pyroCb events: the higher the smoke plume, the larger the aerosol index value. Values over 10 are often associated with such events. The aerosol index values produced by some of the Australian pyroCb events have rivaled that larges ever recorded (image credit: NASA, Colin Seftor)
- At NASA Goddard, satellite data from the OMPS-NM instrument is used to create an ultraviolet aerosol index to track the aerosols and smoke. The UV index is a qualitative product that can easily detect smoke (and dust) over all types of land surfaces. To enhance and more easily identify the smoke and aerosols, scientists combine the UV aerosol index with RGB information.
- Colin Seftor, research scientist at Goddard said, “The UV index has a characteristic that is particularly well suited for identifying and tracking smoke from pyroCb events: the higher the smoke plume, the larger the aerosol index value. Values over 10 are often associated with such events. The aerosol index values produced by some of the Australian pyroCb events have rivaled that largest values ever recorded.”
- Beyond New Zealand, by Jan. 8, the smoke had travelled halfway around Earth, crossing South America, turning the skies hazy and causing colorful sunrises and sunsets. — The smoke is expected to make at least one full circuit around the globe, returning once again to the skies over Australia.
Figure 14: Combining UV aerosol index with RGB information is one way to enhance both (image credit: NASA, Colin Seftor)
- NASA’s satellite instruments are often the first to detect wildfires burning in remote regions, and the locations of new fires are sent directly to land managers worldwide within hours of the satellite overpass. Together, NASA instruments detect actively burning fires, track the transport of smoke from fires, provide information for fire management, and map the extent of changes to ecosystems, based on the extent and severity of burn scars. NASA has a fleet of Earth-observing instruments, many of which contribute to our understanding of fire in the Earth system. Satellites in orbit around the poles provide observations of the entire planet several times per day, whereas satellites in a geostationary orbit provide coarse-resolution imagery of fires, smoke and clouds every five to 15 minutes.
• December 10, 2019: A blast of frigid air from Canada is fueling lake-effect snow in several states downwind of the Great Lakes. The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite captured this image of cloud streets streaming over Lake Superior, Lake Michigan, and Lake Huron on December 10, 2019, using its day-night band. The rows of clouds are created by cold, dry air blowing over warmer lake water in a way that produces parallel cylinders of rotating air that often yield heavy bands of snow. 28)
Figure 15: A blast of cold air from Canada is fueling lake effect snow in several states as shown in this Suomi NPP image of 10 December 2019 (image credit: NASA Earth Observatory image by Joshua Stevens, using VIIRS day-night band data from the Suomi NPP satellite, caption by Adam Voiland)
• November 9, 2019: The bushfire season in New South Wales, Australia, typically runs from October through March. Just one month into the 2019 season, news reports say the amount of burned area has already surpassed that of the past two years combined. 29)
- Three hours after the image of Figure 16 was acquired, the New South Wales Rural Fire Service reported 96 fires burning across the state with 57 that remained uncontained. Seventeen were emergency-level fires—he highest alert level for a bushfire. According to news reports, that’s the highest number of emergency-level fires the state has seen burning at one time.
- Amid the burning, citizens of coastal cities watched their skies turn orange-red and air quality was degraded. In Port Macquarie, the air quality index (a scale that indicates pollution levels) was well into the hazardous category. That’s the level at which everyone is at risk for the pollution to affect their health.
Figure 16: Dry, hot, windy conditions persist as bushfires burn in the eastern part of the Australian state. The recent spate of fires is visible in this image, acquired at 2:30 p.m. local time on November 8, 2019, by the VIIRS (Visible Infrared Imaging Radiometer Suite) on the NOAA-NASA Suomi NPP satellite. The fires burned near the coast from north of Sydney to the border with Queensland, with thick smoke blowing southeast over the Tasman Sea (image credit: NASA Earth Observatory, image by Lauren Dauphin, using VIIRS data from NASA EOSDIS/LANCE and GIBS/Worldview, and the Suomi National Polar-orbiting Partnership. Story by Kathryn Hansen)
- Burning bans have been put in place in some areas amid forecasts for continued severe fire weather—warm temperatures paired with strong winds. The region also has been drier than usual; the lack of rainfall in New South Wales led to one of five driest January-October periods on record.
• September 26, 2019: People in coastal towns along the west coast of southern Africa watched skies turn red on September 25, 2019. Fierce wind picked up and carried huge plumes of sand and dust westward toward the Atlantic Ocean. 30)
- The South African Weather Service reported that the winds lofted enough particles into the air to produce moderate to poor visibility. Indeed, photographs from people in Alexander Bay show dark, hazy skies and streets that are barely visible. According to news reports, aircraft were unable to land at nearby airports.
- The amount of dust lofted from land in the Southern Hemisphere is negligible compared to that of the Northern Hemisphere. Africa’s Sahara Desert, for example, is one of the world’s major dust sources. Still, when winds blow over dry areas of the Southern Hemisphere, dust storms can be fierce. A similar scene unfolded in October 2018, when a thick, narrow plume streamed from the same area.
Figure 17: The plumes were observed on 25 September 2019 at 2:25 p.m. South Africa Standard Time (12:25 Universal Time) with VIIRS on the NOAA/NASA Suomi- NPP satellite. The event covered a wide area north and south of the Orange River, which forms part of the border between Namibia and South Africa (image credit: NASA Earth Observatory image by Lauren Dauphin, using VIIRS data from NASA EOSDIS/LANCE and GIBS/Worldview, and Suomi-NPP. Story by Kathryn Hansen)
• September 13, 2019: Wherever fires are burning around the world NASA-NOAA’s Suomi-NPP satellite’s OMPS (Ozone Mapping and Profiler Suite) can track the smoke and aerosols. On Sept. 13, 2019, data from OMPS revealed aerosols and smoke from fires over both South America and North America. 31)
- Suomi-NPP’s OMPS tracks the health of the ozone layer and measures the concentration of ozone in the Earth's atmosphere and can detect aerosols. Ozone is an important molecule in the atmosphere because it partially blocks harmful ultra-violet radiation from the sun. OMPS data help scientists monitor the health of this vital protective layer.
- OMPS also can be used to measure concentrations of atmospheric aerosols from dust storms and similar events as well as sulfur dioxide (SO2) from volcanic eruptions. One aerosol-related OMPS product is a value known as the “AI (Aerosol Index). The AI value is related to both the thickness and height of the atmospheric aerosol layer. For most atmospheric events involving aerosols, the AI ranges from 0.0 to 5.0, with 5.0 indicating heavy concentrations of aerosols that could reduce visibilities and/or impact health.
Figure 18: Fires in South America generated smoke that continues to create a long plume east into the Atlantic Ocean. Fires over western Brazil were generating aerosols at a level 2.0 on the index. Higher aerosol concentrations, as high as 4.0 were seen off the southeastern coast of Brazil as a result of the fires in the region (image credit: NASA/NOAA, Colin Seftor)
- An aerosol is a suspension of fine solid particles or liquid droplets, in air or another gas. Aerosols can be natural or anthropogenic (manmade). Examples of natural aerosols are fog, dust and geyser steam. Examples of manmade aerosols include haze (suspended particles in the lower atmosphere), particulate air pollutants and smoke.
- High aerosol concentrations not only can affect climate and reduce visibility, they also can impact breathing, reproduction, the cardiovascular system, and the central nervous system, according to the U.S. Environmental Protection Agency. Since aerosols are able to remain suspended in the atmosphere and be carried along prevailing high-altitude wind streams, they can travel great distances away from their source and their effects can linger.
- Fires in South America generated smoke that continues to create a long plume east into the Atlantic Ocean. Fires over western Brazil were generating aerosols at a level 2.0 on the index. Higher aerosol concentrations, as high as 4.0 were seen off the southeastern coast of Brazil as a result of the fires in the region.
Figure 19: In North America, Suomi-NPP’s OMPS detected smoke and aerosols from fires over Canada’s Yukon Territories. Aerosol concentrations were very high over the Yukon fires due to a pyrocumulus event that occurred on 11 September. In the image, there is also light brown area of smoke that looks like a letter “C” on its side. The image also shows a low pressure system (the area of spiraled clouds) off the coast of western Canada (image credit: NASA/NOAA, Colin Seftor)
- In North America, Suomi-NPP’s OMPS detected smoke and aerosols from fires over Canada’s Yukon Territories. Aerosol concentrations were very high over the Yukon fires due to a pyrocumulus event that occurred on September 11.
- Pyrocumulus clouds—sometimes called “fire clouds”—are tall, cauliflower-shaped, and appear as opaque white patches hovering over darker smoke in satellite imagery. Pyrocumulus clouds are similar to cumulus clouds, but the heat that forces the air to rise (which leads to cooling and condensation of water vapor) comes from fire instead of sun-warmed ground. Under certain circumstances, pyrocumulus clouds can produce full-fledged thunderstorms, making them pyrocumulonimbus clouds.
- Scientists monitor pyrocumulus clouds closely because they can inject smoke and pollutants high into the atmosphere. As pollutants are dispersed by wind, they can affect air quality over a broad area.
- The image also contains a light brown area of smoke that looks like a letter “C” on its side and a low pressure system (the area of spiraled clouds) off the coast of western Canada.
- Both images were created at the NASA Goddard Space Flight Center in Greenbelt, Md.
• September 9, 2019: A team of engineers, scientists, and satellite operators recently restored a damaged satellite instrument that is used to measure temperature and water vapor in the Earth’s atmosphere. After the CrIS (Cross-track Infrared Sounder) instrument was damaged by radiation as it flew on the Suomi-NPP satellite, the team made a successful switch to the sensor’s electronic B-side, returning the instrument to full capability. 32)
- Meanwhile, to fill the data gap created by the event, scientists from the JPSS (Joint Polar Satellite System) fast-tracked similar data from Suomi-NPP’s cousin, the NOAA-20 satellite, to the National Weather Service (NWS).
Figure 20: The CrIS instrument, which was damaged and then restored to full capability while on orbit, flies on the Suomi NPP (National Polar-orbiting Partnership) satellite (image credit: NASA)
- The CrIS instrument probes the sky vertically for details on temperature and water vapor — using a process is known as sounding. These observations provide important information on our planet’s atmospheric chemistry and composition, which inform weather forecast centers, environmental data records and field campaign experiments. CrIS can also quantify the distributions of trace gases in the atmosphere, such as carbon dioxide and methane.
- CrIS observes in three spectral bands within the infrared part of the spectrum: shortwave, midwave and longwave. Analysts first detected the anomaly in the midwave data on Saturday, March 23. By Monday, things weren’t looking good, said Flavio Iturbide-Sanchez, the CrIS instrument’s calibration validation lead.
- The midwave band, which includes channels sensitive to water vapor, had stopped reading properly. The next day, measurements from that band had disappeared completely.
- “Midwave is particularly focused on moisture,” said Clayton Buttles, the CrIS chief engineer for L3Harris Technologies, the instrument’s contractor. “Losing that creates a hole in the data products used to generate weather forecast predictions. Ideally, you want to combine all three bands into a comprehensive unit that allows for better forecast and prediction.”
- An algorithm called the NUCAPS (NOAA Unique Combined Atmospheric Processing System), provides the only satellite soundings available to National Weather Service’s weather forecast offices, said Bill Sjoberg, a senior systems engineer with NOAA and JPSS. NUCAPS combines infrared and microwave observations to produce atmospheric profiles of temperature and water vapor, and it relies on CrIS data. Without the CrIS soundings, forecasters would have risked losing the ability to derive an important set of measurements during afternoon hours when severe convection is most common.
- But NOAA-20, which flies 50 minutes ahead, has its own identical CrIS instrument.
- Accelerating access to NOAA-20 satellite soundings for the National Weather Service “helped reestablish the ability to track changes in severe weather conditions,” Sjoberg said.
- Meanwhile, after months of analyzing what went wrong in March, the team determined that the problem with the instrument was likely caused by radiation damage to its midwave infrared signal processor, said David Johnson, NASA’s CrIS instrument scientist. Raw data from the detectors goes through the signal processor, where the data rate gets greatly reduced in size so that it can be efficiently delivered to the ground stations.
- Fortunately, like all of the JPSS instruments and much of the spacecraft, CrIS has redundant parts. It was designed with this threat in mind. It contains a “Side 2,” a fully functional backup set of electronics, which the team hoped had not been damaged. “But we wouldn’t know without making the switch,” Iturbide-Sanchez said.
- For three months, the team studied the instrument. They ran a “reliability analysis.” They weighed the risks. They “located and verified all configuration files for Side 2,” Johnson said.
- On June 21, the team made the official decision to switch to Side 2, and three days later, they executed the switch. The turn-on process involved tuning the instrument and checking settings. But Iturbide-Sanchez knew almost immediately that the three bands were working.
- The plan was to complete the turn-on in two weeks. They did it in five days, a result of working long hours and frequent communication with ground station command. And by early July, satellite soundings had been recovered and the product was good enough to be used in weather models.
- It was very much a team effort, Iturbide-Sanchez and Johnson both said: The Cooperative Institute for Meteorological Satellite Studies at the University of Wisconsin and the Joint Center for Earth System’s Technology at the University of Maryland, Baltimore County, worked with the team during both phases, contributing to the preparation of a configuration file before the side switch, and evaluating data quality after.
- “NOAA invests in redundant systems to maximize the useful life of the instruments,” said Jim Gleason, NASA project scientist for JPSS. “This is a story of the system working as designed.”
- Making the successful switch from Side 1 to Side 2 also allows for National Weather Service products that provide early warnings for events like hurricanes, Buttles said: “We would all be worse off if we didn’t have that data.”
Figure 21: An engineer works on the CrIS instrument for the JPSS-2 satellite, which is slated to launch in March 2022. The CrIS instrument also flies on the Suomi-NPP satellite, and was recently restored to full capability after getting damaged while on orbit (image credit: L3Harris Technologies)
• September 6, 2019: After devastating the Bahamas and grazing Florida and Georgia, Hurricane Dorian rebounded and raked the coast of South Carolina with strong winds, heavy rains, and a storm surge. Wind, falling trees, and flooding damaged power infrastructure in coastal areas of the southeast U.S. 33)
- The VIIRS sensor observed thick cloud bands circulating around Dorian’s large eye, the part of the storm with mostly calm weather and the lowest atmospheric pressure. Hurricane eyes average about 20 miles (32 kilometers); the National Hurricane Center reported Dorian’s eye had a diameter of 50 miles (80 kilometers) around the time this image was acquired. Thinner clouds—part of the storm’s higher-level outflow—extended well inland across Georgia, South Carolina, and North Carolina.
Figure 22: VIIRS on on the Suomi NPP satellite captured this nighttime composite image as the storm approached the coast at 3:42 a.m. Eastern Time (07:42 UTC) on 5 September 2019. At the time, Dorian packed maximum sustained winds of 115 miles (185 kilometers) per hour and was moving north at 8 miles per hour (image credit: NASA Earth Observatory, image by Joshua Stevens, using VIIRS data from the Suomi NPP satellite. Story by Adam Voiland)
Figure 23: The VIIRS image was captured by the sensor’s day-night band, which detects light in a range of wavelengths from green to near-infrared and uses filtering techniques to observe signals such as gas flares, city lights, and reflected moonlight. Infrared observations from VIIRS were used to enhance the visibility of clouds. Optical MODIS satellite data was layered into the image to make it easier to distinguish between ocean and land surfaces (image credit: NASA Earth Observatory, image by Joshua Stevens, using VIIRS data from the Suomi NPP satellite, and power outage data courtesy of PowerOutage.us. Story by Adam Voiland)
• August 20, 2019: Beginning on August 10, 2019, NASA satellites have observed waves of fire sweeping through forests on Gran Canaria, the second most populous of the Canary Islands. Though the fire has not yet struck major residential and tourist areas, authorities have issued evacuation orders for 9,000 people living in 50 nearby towns and villages. 34)
- The fire is tearing through pine forests in mountainous terrain on the second most populous of the Canary Islands.
Figure 24: VIIRS on the Suomi NPP satellite tracked the growth of the fire between 14-19 August 2019. The VIIRS “day-night band” is extremely sensitive to low light, making it possible to see the fire front from space at night. Nighttime lights from population centers along Gran Canaria’s coast are also visible, particularly along the eastern half of the island (image credit: NASA Earth Observatory, images by Joshua Stevens, using data from the VIIRS day-night band data from the Suomi NPP. Story by Adam Voiland)
- The fire initially flared up near Tejeda, in the mountainous central part of the island, and then spread rapidly toward the northwest into Tamadaba Natural Park in unusually warm, dry, and windy conditions.
Figure 25: This map shows land surface temperatures on the afternoon of August 15, a day when temperatures exceeded 49°C (120°F) in some areas. The map is based on data collected by the MODIS instrument on NASA's Aqua satellite. Note that the map depicts land surface temperatures, not air temperatures. Land surface temperatures reflect how hot the surface of the Earth would feel to the touch in a particular location. They can sometimes be significantly hotter or cooler than air temperatures. (image credit: NASA Earth Observatory, image by Joshua Stevens, using data from the Level 1 and Atmospheres Active Distribution System (LAADS) and Land Atmosphere Near real-time Capability for EOS (LANCE), story by Adam Voiland)
- The fire is burning forests of Canary pine (Pinus canariensis), which is among the most fire-tolerant pine species in the world. The trees have several adaptations that allow them to survive and thrive after fires: thick bark that prevents heat damage, trunks that easily sprout new branches; and serotinous cones that depend on high heat to release seeds.
Figure 26: MODIS acquired this false-color image on 19 August. It is composed from a combination of visible and infrared light (MODIS bands 7-2-1) that help distinguish charred vegetation (black) from unburned vegetation (green). Areas with minimal vegetation appear brown (image credit: NASA Earth Observatory, image by Joshua Stevens, using data from the Level 1 and Atmospheres Active Distribution System (LAADS) and Land Atmosphere Near real-time Capability for EOS (LANCE), story by Adam Voiland)
- Scientists who monitor fire activity in the Canary Islands have observed clear trends in the past half-century. Most notably, the number of fires has decreased even as the number of hectares burned by each fire has increased significantly. On net, fires burn roughly the same average area each year, but they do it in a much more dramatic fashion because they are larger and more intense.
- While increasing temperatures may have contributed to this trend, University of La Laguna scientist José Ramón Arévalo attributes much of the change to more active and effective firefighting efforts that now suppress most fires and lead to a build-up of flammable material in forests. Increased development and tourism also contribute by requiring that firefighters aggressively suppress fires over a wider area.
• August 19, 2019: Our atmosphere behaves like a fluid, changing its flow and direction when it runs into an obstacle. Sometimes we can see (and feel) these movements on a small scale, as winds blow trees and water. Satellites, however, can observe these twists and bends on a broad scale as they create interesting shapes in the sky. 35)
Figure 27: This image shows spiraling cloud patterns off the coast of Morocco on 19 July 2019. Known as von Kármán vortices, these eddies can form nearly anywhere that fluid flow is disturbed by a solid object. In this case, the vortices formed when winds flowed around small islands in the North Atlantic (image credit: NASA Earth Observatory, image by Joshua Stevens, using VIIRS day-night band data from the Suomi NPP. Story by Kasha Patel, with image interpretation by George Young)
- “The basic idea is that flow over, and around, a mountainous island slows down,” said George Young, professor of meteorology at Penn State University. This creates a vertical wall of whirling air—with faster wind flowing past slower wind below. These sheets can wrap themselves into vortices and shed alternately off the two sides of the island. They can subsequently travel downwind from the island to create “vortex streets,” as seen in this image. The pattern of the spirals depends on the intensity of the wind.
- “This is a spectacular satellite image,” said Paul Beggs, an associate professor at Macquarie University. “I don’t recall having seen an image of von Kármán vortices at nighttime previously, so I would consider it rare.” Atmospheric vortices are commonly observed by satellites, and Earth Observatory has shown them many times. But we have rarely noted them in nighttime imagery.
- Young notes that nighttime von Kármán vortices are not necessarily infrequent occurrences; new sensor technology has just made it much easier to capture these scenes. Satellites now carry shortwave infrared channels and image filters that achieve the spatial resolution and faint light detection to allow researchers to see vortices at night.
- This image was acquired with the “day-night band” of the VIIRS instrument on the Suomi NPP satellite. VIIRS 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.
- “I’m not the least surprised to see them at night because the two factors they primarily depend on (wind speed in the boundary layer and a strong stable layer at the top of the boundary layer) vary little between day and night at sea,” said Young. These von Karman vortices also appeared in daylight.
• August 10, 2019: Twin typhoons continued to churn across the Western Pacific Ocean late this week, threatening East Asian countries with destructive winds and rain. When this image was acquired on August 9, 2019, Typhoon Lekima (left) was skirting north of Taiwan and aiming for eastern China. 36)
- Although Taiwan avoided a direct hit from Typhoon Lekima, the storm’s outer bands still delivered strong rains and wind, causing flooding and power outages. According to China’s Central Weather Bureau, parts of the country’s northern mountains received as much as 390 mm (15 inches) of rain from 8-10 August. The rainfall increased the risk of landslides after a magnitude 6.0 earthquake rattled Taiwan on 8 August.
- Lekima next aimed for China’s Zhejiang Province. According to the Joint Typhoon Warning Center, the typhoon is expected to make landfall early on 10 August, about 325 km (200 miles) south of Shanghai. Forecasters expect it will then track northward. The cities labeled on the image all have populations of more than 1.5 million people.
Figure 28: The image, captured by VIIRS on the Suomi NPP satellite, shows the storm on 9 August 2019 at 05:30 Universal Time (1:30 p.m. China Standard Time). Around that time, the storm was moving toward the northwest with maximum sustained winds of 105 knots (120 miles/195 km/hr), making it a category 3 storm on the Saffir-Simpson wind scale (image credit: NASA Earth Observatory, image by Joshua Stevens, using VIIRS data from NASA EOSDIS/LANCE and GIBS/Worldview, and the Suomi National Polar-orbiting Partnership. Story by Kathryn Hansen)
- Officials in China have issued a red alert, the highest of four levels on the country’s typhoon warning system. According to news reports, thousands of people in Shanghai were asked to prepare to evacuate. Transportation authorities have canceled large numbers of flights, halted trains, a rerouted cruise ships.
- Meanwhile, Typhoon Krosa (right) had maximum sustained winds of 85 knots (100 miles/155 km/hr), making it a category 2 storm when the image was acquired. Krosa continues to follow a more northerly path toward Japan, but the track forecasted for this storm remains uncertain.
• May 22, 2019: Some residents of the town of High Level, Canada, were told on May 20 to evacuate in the face of a large and out-of-control wildfire that has started advancing toward the town. 37)
- The Chuckegg Creek wildfire started on May 12, 2019, and mostly burned northwest and away from populated areas. On May 18, residents told news media about thick clouds of black smoke, an ominous sign but still a distant threat. By May 19, the fire had charred at least 25,000 hectares (60,000 acres), according to statistics from provincial officials at Alberta Wildfire.
- On May 20, the fire took a turn and advanced within 5 km of High Level (population 3,000). It had spread across an estimated 69,000 hectares, leading the Alberta Emergency Management Agency to issue a mandatory evacuation order for residents south and southeast of the town. A state of emergency was declared for Mackenzie County.
- Electric power outages were reported in High Level, First Nation reserves, and across parts of Mackenzie County. Fire managers warned of extreme fire danger due to warm air temperatures, low humidity, gusty winds, and no precipitation in the near-term forecast. Alberta Wildfire deployed more than 60 firefighters along with heavy equipment, helicopters, and air tankers to contain this fire, while requesting more resources from the province.
Figure 29: VIIRS on the Suomi NPP satellite acquired this natural-color image of northern Alberta in the early afternoon of May 19, 2019. (image credit: NASA Earth Observatory, image by Joshua Stevens, using VIIRS data from NASA EOSDIS/LANCE and GIBS/Worldview, and the Suomi National Polar-orbiting Partnership. Story by Mike Carlowicz)
- The Chuckegg Creek wildfire was one of six burning out of control in northern and central Alberta Province as of May 20, 2019. The provincial government recorded 11 other fires as being under control and three as “being held” (not likely to grow past expected boundaries). Fire bans and off-road vehicle restrictions were in place in much of the northern tier of Alberta.
Figure 30: VIIRS on the Suomi NPP satellite acquired this natural-color image of northern Alberta in the early afternoon of May 19, 2019 (image credit: NASA Earth Observatory, image by Joshua Stevens, using VIIRS data from NASA EOSDIS/LANCE and GIBS/Worldview, and the Suomi National Polar-orbiting Partnership. Story by Mike Carlowicz)
- The fires have sprung up in a time that ecologists refer to as the “spring dip.” Scientists have noted for years that forests in Canada and around the Great Lakes in the United States are especially susceptible to fire in the late spring because trees and grasses reach a point of extremely low moisture content (a dip) between the end of winter and the start of new seasonal growth. The effect is not yet well understood, as it also involves subtle changes in plant chemistry.
• May 07, 2019: It is not even summertime, but already the United Kingdom has seen a significant number of wildfires. The map above shows cumulative fire detections across the United Kingdom from January 1 through April 30, 2019. The data come from the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite. 38)
- Each red dot depicts one fire detection from the VIIRS 375-meter active fire data product. A “fire detection” is a pixel in which the sensor and an algorithm indicated there was active fire on any given day. Many fire detections can be generated by a single burning fire.
- Notable fires this year include blazes in February and April in England’s Ashdown Forest—the setting that inspired the Hundred Acre Wood in A.A. Milne’s Winnie the Pooh stories. In late February, following the United Kingdom’s warmest winter day on record, the Marsden Moor fire burned in West Yorkshire, England. Scotland has seen burning too, including a major wildfire that burned near a wind farm in Moray.
Figure 31: Fires in the UK, detected by the VIIRS instrument on Suomi NPP in the period January 1 - April 30, 2019 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using VIIRS data from the Suomi National Polar-orbiting Partnership. Story by Kathryn Hansen)
Figure 32: This chart shows that there is a seasonal trend to the number of fire detections. Vegetation that was previously frozen and dried during the winter becomes fuel for wildfires during spring and summer months (image credit: NASA Earth Observatory, image by Lauren Dauphin, using VIIRS data from the Suomi National Polar-orbiting Partnership. Story by Kathryn Hansen)
- Notice that there have been more fire detections since 2017 compared with previous years. According to the annual report on forest fires by the European Commission’s Joint Research Center, warm, dry weather was responsible for the rise in wildfire numbers across the United Kingdom in 2017. A similar situation played out in 2018.
- “Drier-than-normal conditions can boost fire detections in two ways,” said Wilfrid Schroeder, a scientist at the University of Maryland and principal investigator for the VIIRS active fire product. He noted that dry conditions favor the ignition and spread of fire. There also tends to be less cloud coverage, making fires more likely to be detected from space.
- High fire counts and warm, dry weather have been a continuing trend. By the end of April 2019, the United Kingdom had already seen more fires through this point in the year than in the record-breaking year of 2018.
• May 01, 2019: Between November and April, Harmattan trade winds carry vast amounts of mineral dust from the Sahara Desert across West African skies toward the Gulf of Guinea. The pall of dust that hangs over the region is known as the Harmattan haze—which, fittingly, means “tears your breath apart” in Twi, a common West African language. 39)
- West Africans have long known the haze season to be one of dry skin and chapped lips, but a recent study led by Susanne Bauer of NASA’s Goddard Institute for Space Studies suggests that dusty skies are more than a nuisance. Her analysis indicates that they are deadly for hundreds of thousands of people each year.
- Bauer became focused on the health impacts of dust somewhat indirectly. After completing a study in 2015 that found fertilizer use on farms was a surprisingly large source of air pollution, she wondered if there were other unexpected ways that food production was affecting air quality.
Figure 33: The VIIRS instrument on the Suomi NPP satellite acquired this image of dust spreading across West Africa on February 2, 2019. One of the largest sources of dust in the Sahara is the Bodélé Depression, a dried lake-bed in northern Chad that is rich with silt and fine-grained dust. The alignment of nearby mountain ranges functions like a wind tunnel, funneling strong winds over the depression on a regular basis (image credit: NASA Earth Observatory, image by Lauren Dauphin, using VIIRS data from the Suomi NPP. Story by Adam Voiland)
- This prompted her to look closely at fires in Africa. Every year, satellites detect thousands of manmade fires that come and go in sync with the seasons. Most of these fires are ignited to clear or fertilize crops, kill pests, and manage grasslands.
- Agricultural fires generate so much smoke that Bauer guessed they were one of the biggest sources of fine aerosol particles (PM2.5)—the particle size that causes the most serious health problems. (Fine particles can penetrate more easily into the human respiratory and circulatory system than larger particles.)
- Bauer and colleagues tried to confirm her suspicion by running a computer simulation of how smoke, desert dust, industrial haze, and other airborne particles (aerosols) moved and evolved in African skies with changing weather and environmental conditions. The model simulated conditions in 2016, a year when researchers had ample data from satellites and from field campaigns.
- To Bauer’s surprise, the analysis showed that the smoke had a smaller effect on people’s health than dust. “What we have is one of the most prolific sources of dust in the world—the Sahara Desert—regularly blowing large amounts of dust into densely populated countries in West Africa,” she explained. “When all of the dust mixes with air pollution from vehicles and factories in cities, the air becomes extremely unhealthy.” In contrast, smoke from crop fires tends to be concentrated in rural areas with relatively few people.
- By combining the results of several simulations with information about the health effects of breathing fine particles, Bauer and colleagues concluded that air pollution in Africa likely caused the premature deaths of about 780,000 people in 2016, more than the number killed by HIV/AIDS. They attributed about 70 percent of these deaths to dust, 25 percent to industrial pollution, and just 5 percent to smoke from fires. The effects of dust were especially pronounced in West African nations including Nigeria and Ghana.
- “Air pollution is of overwhelming importance to public health in Africa, yet it is hardly on the radar in most countries,” said Bauer. “Except in South Africa, there are virtually no routine measurements of PM2.5; few people understand that too much exposure to air pollution can shorten lives.”
• April 17, 2019: Don’t blink or you might miss some of Earth’s most spectacular transitions. As spring tightens its grip on the Northern Hemisphere, natural events like rainfed wildflower blooms, wind-stirred sediment swirls, and melting lake ice can fade as fast as they formed. 40)
- How long will it take Lake Balkash to become entirely ice free? In the past, the full transition has happened in a matter of weeks; check out this image pair from April 11 and 18, 2003. Water and air temperatures at this time of year are climbing, and the region is commonly windy, which can help break up lake ice.
- Notice that in areas where ice has already released its grip, the water appears in brilliant turquoise. That’s in part because the lake is extremely shallow—averaging 4.3 meters deep on the western side—which makes it easier for winds to stir up sediments from the bottom.
Figure 34: Lake Balkhash, spanning about 17,000 km2 (6,600 square miles) in southeastern Kazakhstan, is one of Asia’s largest lakes. Despite the lake’s large size, winters are harsh enough to keep the lake frozen over from November through March. By April 8, 2019, when the Visible Infrared Imaging Radiometer Suite (VIIRS) on Suomi NPP acquired this image, the spring thaw was underway. Images from just a week before show the lake almost entirely covered with ice (image credit: NASA Earth Observatory, image by Lauren Dauphin, using VIIRS data from the Suomi National Polar-orbiting Partnership. Story by Kathryn Hansen)
- Most of the water feeding the western portion of the lake comes from the Ili River, which is fed by meltwater runoff originating in the Tien Shan Mountains. (Part of that mountain chain, the Borohoro Range, is pictured with caps of snow and ice.) Research has found that degrading glaciers and melting snow in the Tien Shan have led to increases in the water level of Lake Balkash in recent decades. However, the authors note that if glacier degradation and melt continue, water level increases could quickly shift to decreases.
• April 16, 2019: For the second time in a month, an intense spring “bomb cyclone” plastered the Upper Midwest of the United States with snow and wind. While the April storm was not quite as strong as the blizzard in March, several states were hit with more than 12 inches (30 cm) of snow and by wind gusts exceeding 50 miles (80 km) per hour. 41)
- On April 10-12, 2019, whiteout conditions clogged roadways, caused tens of thousands of homes to lose power, and grounded hundreds of flights, according to news reports. South Dakota was one of the hardest hit states, with more than 24 inches (60 cm) of snow falling across much of the state.
- Many rivers in the region were already swollen with water (dark blue) before the storm arrived. Forecasters are wary that the influx of new snow could trigger new floods in the coming weeks; at a minimum, rivers will be high in the coming days. A few rivers in South Dakota—most notably the James and Big Sioux—were well above flood stage on April 15.
- The storm’s reach extended well beyond the Upper Midwest. As it pushed across the middle of the continent, it pulled in warm, dry air from the Southwest. Several meteorologists noted that it carried enough dust from Texas to color the snow in South Dakota and Minnesota in shades of yellow, brown, and orange.
Figure 35: On April 8 and 13, 2019, the VIIRS instrument on the Suomi NPP satellite captured these false-color images. With this combination of visible and infrared light (bands M11-I2-I1), snow appears light blue and clouds white. Bare land is brown. You can see a natural-color version of the image here (image credit: NASA Earth Observatory, image by Lauren Dauphin, using VIIRS data from the Suomi NPP, Story by Adam Voiland)
• April 9, 2019: In late March 2019, tropical cyclone Veronica made landfall along the Pilbara coast in Western Australia. Dropping more than 46 cm (18 inches) of rain in some areas within 72 hours, the storm caused major flooding and spurred several home evacuations. The destructive winds and the rainfall runoff also stirred up offshore waters, with lingering effects. 42)
Figure 36: This image shows discolored water offshore from Port Hedland on March 29, 2019, as observed by the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument on Suomi NPP. The satellite imagery shows what is likely a combination of suspended sediment and phytoplankton blooms appearing by March 27 and continuing through April 2, 2019 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using VIIRS data from the Suomi National Polar-orbiting Partnership data from NASA EOSDIS/LANCE. Story by Kasha Patel)
Figure 37: The Australian Bureau of Meteorology reported that a phytoplankton bloom was taking place at the time. This image shows concentrations of chlorophyll, the pigment that phytoplankton use to harvest sunlight, as derived by the Moderate Resolution Imaging Spectroradiometer (MODIS) on March 29, 2019 (image credit: NASA Earth Observatory, image by Lauren Dauphin, using MODIS data from NASA EOSDIS/LANCE and GIBS/Worldview. Story by Kasha Patel)
- Past studies have shown that cyclonic winds can stir up ocean waters and bring nutrients to the surface, promoting blooms of phytoplankton. In coastal waters, nutrients often come from the resuspension of seafloor sediments and from river runoff.
- “Sometimes you can see a bloom last for many days over the open ocean after a tropical cyclone has passed,” said Sen Chiao, meteorologist at San Jose State University and director of the NASA-funded Center for Applied Atmospheric Research and Education. Chiao added that Veronica seems to have pulled cooler water up from the ocean depths to the surface (upwelling), which provided more nutrients.
- A similar bloom also followed a tropical cyclone a few years ago in the same region of Western Australia.
• March 26, 2019: On March 15, 2019, Tropical Cyclone Idai pummeled through eastern Africa causing catastrophic flooding, landslides, and large numbers of causalities across Mozambique, Malawi, and Zimbabwe. More than half a million people in Mozambique were affected, with the port city of Beira experiencing the most damage.43)
- The nighttime images of Beira’s nighttime lights (Figure 38) are based on data captured by the Suomi NPP satellite. The data were acquired by the VIIRS (Visible Infrared Imaging Radiometer Suite) “day-night band,” which detects light in a range of wavelengths from green to near-infrared, including reflected moonlight, light from fires and oil wells, lightning, and emissions from cities or other human activity. The base map makes use of data collected by the Landsat satellite.
- Note that these maps are not showing raw imagery of light. A team of scientists from NASA’s Goddard Space Flight Center and Marshall Space Flight Center processed and corrected the raw VIIRS data to filter out stray light from the Moon, fires, airglow, and any other sources that are not electric lights. Their processing techniques also removed as much other atmospheric interference—such as dust, haze, and thin clouds—as possible.
Figure 38: The image on the left shows the extent of electric lighting across Beira on March 9, 2019, a typical night before the storm hit; the image on the right shows light on March 24, 2019, three days after Idai had passed. Most of the lights in Manga, Matacuane, and Macuti appeared to be out. According to news reports, the storm destroyed nearly 90 percent of the city (image credit: NASA Earth Observatory, images by Joshua Stevens, using Black Marble data courtesy of Ranjay Shrestha/NASA Goddard Space Flight Center, and Landsat data from the U.S. Geological Survey. Story by Kasha Patel)
• March 23, 2019: Two severe tropical cyclones bore down on northern Australia at the start of autumn 2019. Cyclone season in the region stretches from November to April, peaking in February and March. 44)
- Cyclone Trevor first made landfall on the Cape York Peninsula as a category 3 storm on March 20. The storm weakened and meandered over land before intensifying again to a category 4 storm over the warm waters of the Gulf of Carpentaria (about 31 degrees Celsius). The government of the Northern Territory declared a state of emergency and launched the largest evacuation in the state since 1974.
- Trevor is predicted to make landfall again on March 23, bringing intense winds, a storm surge, and widespread rainfall of 100 to 200 mm (4 to 8 inches), with some areas seeing up to 300 mm (12 inches). Some inland desert areas could see as much rain in a few days as they receive across some entire years.
- At the same time, Cyclone Veronica was approaching Western Australia and headed for possible landfall on the Pilbara Coast by March 23 or 24. Veronica developed from a tropical low pressure system to a category 4 storm on March 20. The Australian Bureau of Meteorology has advised: “Widespread very heavy rainfall conducive to major flooding is likely over the Pilbara coast and adjacent inland areas over the weekend. Heavy rainfall is expected to result in significant river rises areas of flooding and hazardous road conditions.”
Figure 39: On March 22, 2019, VIIRS (Visible Infrared Imaging Radiometer Suite) on the Suomi NPP satellite acquired the data to make this composite image. The seam line across Australia marks the edge of two different early afternoon satellite passes over the continent. At the time of the image, cyclones Trevor and Veronica both had sustained winds of roughly 175 km/hr (image credit: NASA Earth Observatory, image by Lauren Dauphin, using VIIRS data from Suomi NP, story by Mike Carlowicz)
• February 28, 2019: The Manaro Voui volcano on the island of Ambae in the nation of Vanuatu in the South Pacific Ocean made the 2018 record books. A NASA-NOAA satellite confirmed Manaro Voui had the largest eruption of sulfur dioxide that year. 45) 46)
- The volcano injected 400,000 tons of sulfur dioxide into the upper troposphere and stratosphere during its most active phase in July, and a total of 600,000 tons in 2018. That’s three times the amount released from all combined worldwide eruptions in 2017.
- During a series of eruptions at Ambae in 2018, volcanic ash also blackened the sky, buried crops and destroyed homes, and acid rain turned the rainwater, the island’s main source of drinking water, cloudy and “metallic, like sour lemon juice,” said New Zealand volcanologist Brad Scott. Over the course of the year, the island’s entire population of 11,000 was forced to evacuate.
- At the Ambae volcano’s peak eruption in July, measurements showed the results of a powerful burst of energy that pushed gas and ash to the upper part of the troposphere and into the stratosphere, at an altitude of 10.5 miles. Sulfur dioxide is short-lived in the atmosphere, but once it penetrates into the stratosphere, where it combines with water vapor to convert to sulfuric acid aerosols, it can last much longer — for weeks, months or even years, depending on the altitude and latitude of injection, said Simon Carn, professor of volcanology at Michigan Tech.
- In extreme cases, like the 1991 eruption of Mount Pinatubo in the Philippines, these tiny aerosol particles can scatter so much sunlight that they cool the Earth’s surface below.
Figure 40: This map shows stratospheric sulfur dioxide concentrations on July 28, 2018, as detected by OMPS on the Suomi-NPP satellite, when Ambae was at the peak of its sulfur emissions. For perspective, emissions from Hawaii’s Kilauea and the Sierra Negra volcano in the Galapagos are shown on the same day (image credit: Image by Lauren Dauphin, NASA Earth Observatory, using OMPS data from GES DISC and Simon Carn)
- The OMPS nadir mapper instruments on the Suomi-NPP and NOAA-20 (JPSS-1) satellites contain hyperspectral ultraviolet sensors, which map volcanic clouds and measure sulfur dioxide emissions by observing reflected sunlight. Sulfur dioxide (SO2) and other gases like ozone each have their own spectral absorption signature, their unique fingerprint. OMPS measures these signatures, which are then converted, using complicated algorithms, into the number of SO2 gas molecules in an atmospheric column.
Figure 41: The plot shows the July-August spike in emissions from Ambae (image credit: Image by Lauren Dauphin, NASA Earth Observatory, using OMPS data from GES DISC and Simon Carn)
- “Once we know the SO2 amount, we put it on a map and monitor where that cloud moves,” said Nickolay Krotkov, a research scientist at NASA Goddard’s Atmospheric Chemistry and Dynamics Laboratory.
- These maps, which are produced within three hours of the satellite’s overpass, are used at volcanic ash advisory centers to predict the movement of volcanic clouds and reroute aircraft, when needed.
- Mount Pinatubo’s violent eruption injected about 15 million tons of sulfur dioxide into the stratosphere. The resulting sulfuric acid aerosols remained in the stratosphere for about two years, and cooled the Earth’s surface by a range of 1 to 2 degrees Fahrenheit.
- This Ambae eruption was too small to cause any such cooling. “We think to have a measurable climate impact, the eruption needs to produce at least 5 to 10 million tons of SO2,” Carn said.
- Still, scientists are trying to understand the collective impact of volcanoes like Ambae and others on the climate. Stratospheric aerosols and other volcanic gases emitted by volcanoes like Ambae can alter the delicate balance of the chemical composition of the stratosphere. And while none of the smaller eruptions have had measurable climate effects on their own, they may collectively impact the climate by sustaining the stratospheric aerosol layer.
- “Without these eruptions, the stratospheric layer would be much, much smaller,” Krotkov said.
Figure 42: The natural-color image above was acquired on July 27, 2018, by the Visible Infrared Imaging Radiometer Suite (VIIRS) on Suomi NPP (image credit: Lauren Dauphin, NASA Earth Observatory)
• January 28, 2019: Large fires fueled by extremely dry and hot conditions have been burning for almost two weeks in central and southeast Tasmania, the southernmost state of Australia. This image was acquired on January 28, 2019, by the VIIRS (Visible Infrared Imaging Radiometer Suite) on the Suomi NPP satellite. 47)
- As of January 28, the Tasmania Fire Service reported 44 fires. The Great Pine Tier fire in the Central Plateau had burned more than 40,000 hectares. The Riveaux Road fire in the south had burned more around 14,000 hectares. News outlets reported smoke from some of the fires was visible as far away as New Zealand.
- The Tasmania Fire Service issued several emergency warnings to residents to relocate, as dangerous fire conditions and strong wind persist.
Figure 43: Suomi NPP image of the southernmost island state of Australia, located 240 km to the south of the Australian mainland, captured on 28 January 2019 with VIIRS instrument showing the various fires (image credit: NASA Earth Observatory image by Lauren Dauphin, using VIIRS data from Suomi NPP, text by Kasha Patel)
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. 48)
Figure 44: 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. 49) 50) 51)
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 5: 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 6: 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 45: Functional block diagram of ATMS (image credit: NASA)
Figure 46: Schematic illustration of ATMS (image credit: NASA)
Figure 47: Elements of the ATMS design configuration (image credit: NASA)
Figure 48: 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 49: Photo of the ATMS instrument (image credit: NASA) 52)
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 7).
• 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. 53)
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). 54) 55) 56) 57) 58) 59) 60) 61)
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 50: 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 8. 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 51: 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: 62) 63) 64)
• 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. 65)
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. 65).
Figure 52: 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. 66)
Figure 53: 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 9: Overview of the FPA design of VIIRS
Some key EDRs of VIIRS: 67)
• 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. 68)
Figure 54: Photo of the VIIRS instrument (image credit: NASA, Raytheon) 69)
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. 70)
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: 73)
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.
Figure 55: An animated video demonstrating the path light travels through an exploded view of the Visible/Infrared Imaging Radiometer Suite (VIIRS) sensor. The VIIRS sensor payload launched aboard the Suomi NPP (National Polar-orbiting Partnership) remote sensing weather satellite on Oct. 28, 2011. Raytheon also built and manages the CGS (Common Ground System) which processes and disseminates the data from the NPP satellite and payloads (video credit: Raytheon, Published on 31 October 2018)
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). 74)
Figure 56: 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 10. Since L determines the unapodized spectral resolution, the nominal value for L is also given in the table. 75)
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. 76)
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]. 77)
• 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 11: 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. 78)
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. 79)
Figure 57: Illustration of the CrIS instrument (image credit: IPO)
Figure 58: 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 12: CrIMSS mission products (EDRs)
Figure 59: 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: 80)
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.
Legend to Figure 60: 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. 81) 82) 83)
Table 13: Overall mission requirements for OMPS ozone observations 84)
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 61: 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: 85)
- 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 62: 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. 86)
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. 87)
Figure 63: 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 14: 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. 88)
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: 89) 90) 91) 92) 93) 94)
- 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 64: Cross section of the CERES telescope (image credit: NASA/LaRC) 95)
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: 96)
• 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 15: CERES instrument parameters
Figure 65: NPP CERES data system architecture (image credit: NASA/LaRC)
Figure 66: Photo of the CERES flight modules in 1999 (image credit: NASA)
Figure 67: Illustration of the CERES instrument (image credit: NASA/LaRC)
Figure 68: Engineers inspect the CERES FM-25 sensor following the completion of thermal vacuum testing at NGC (image credit: NGC) 97)
Table 16: 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 70: Suomi NPP mission system architecture (NASA, NOAA)
Figure 71: SDS (Science Data System) architecture (image credit: NASA) 99)
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. 100) 101)
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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).