WSF-M (Weather System Follow-on - Microwave) Satellite
The U.S. Air Force’s future weather satellite plans are beginning to take shape but are centered around enhancing information technology, cybersecurity and small satellites in the near term rather than a new generation of large, sophisticated spacecraft to replace the Defense Meteorological Satellite Program. 1)
That’s largely due to budget constraints and the fact that accurate forecasting, while critical to military operations, is not the service’s primary mission, according to current and former government officials who asked not to be quoted. The Air Force is moving ahead with plans to buy satellites to fulfill its requirements for microwave, electro-optical and infrared observations.
The Air Force SMC (Space and Missile Systems Center) awarded Ball Aerospace & Technologies Corp. a contract in November 2017 to build two satellites equipped with passive microwave imaging radiometers and Energetic Charged Particle sensors to send into LEO (Low Earth Orbit). The Air Force plans to include Energetic Charged Particle sensors on all future satellites to enhance its space weather observations.
To bridge the gap created by the end of Defense Meteorological Satellite-19 operations, the Air Force plans to work with the Pentagon’s Operationally Responsive Space Office to launch a small satellite with electro-optical and infrared imagers in 2021 or 2022 to characterize clouds.
Due to the quick timeline of this gap-filler program, companies would have approximately two years to build the passive microwave imaging radiometer.
Harris Corp. is one of the companies eager to do that. Harris would build it by relying on the heritage of imagers it built for the U.S. National Oceanic and Atmospheric Administration’s Polar Operational Environmental Satellites, said Eric Webster, Harris environmental solutions vice president and general manager.
In addition, the Air Force began soliciting proposals Nov. 27 from industry for Weather System Follow-on satellites equipped with instruments to characterize clouds and provide imagery in theaters of combat. The first satellite in this new Weather Satellite Follow-on Electro-optical/Infrared constellation (WSF-E) would be launched around 2024 and like DMSP would cross the equator early in the morning local time, according to the request for proposals.
Visible Infrared Imaging Radiometer Suite (VIIRS), which NOAA flies on the Suomi NPP (National Polar-orbiting Partnership) satellite and NOAA-20, the first Joint Polar Satellite System spacecraft, is a candidate for the WSF-E mission. The VIIRS sensor was designed to fulfill NASA, NOAA and Defense Department requirements as part of the cancelled National Polar-orbiting Operational Environmental Satellite System program. Some VIIRS capabilities like its day-night imagery stem from military requirements.
“To a large extent VIIRS on Suomi NPP and JPSS-1 is already doing the WSF-E mission,” said Robert Curbeam, Raytheon Space Systems director. “Obviously because that data is available, the military uses it. They also use a lot of data products that use VIIRS data: sea surface temperature, ocean color, turbidity, littoral transport,” said Curbeam, a former astronaut and U.S. Navy captain.
To bolster its weather satellite constellation, the Air Force also is considering using one of NOAA’s Geostationary Operational Environmental Satellites fill a gap in coverage over the Indian Ocean.
“We are working with the Air Force to offer up one of our retired GOES N, O, P satellites for that transfer,” said Steve Volz, NOAA acting assistant secretary for environmental observation and prediction. “With GOES-16 functioning, we are in a robust situation. We can afford to give the Air Force one of our spares. We have two backups; we only need one.”
GOES N, O, P are NOAA’s generation of satellites that preceded the GOES-R constellation that is beginning to take shape with the November 2016 launch of GOES-16 and the anticipated launch of GOES-S in March.
• May 18, 2020: It's not easy to be able to conduct critical scientific design reviews while observing the health and safety rules of the COVID-19, but both elements were maintained at the United States Space Force’s Space and Missile Systems Center’s Weather System Follow-on-Microwave (WSF-M) program. Here two major milestones were achieved despite facing these challenges. 2)
- First, the WSF-M system Critical Design Review completed in April, ensuring that the WSF-M system can meet stated performance requirements within cost, schedule and risk expectations; and is ready to proceed with fabrication, demonstration and test efforts. This multi-disciplined review was successfully conducted while adhering to the current requirements for physical distancing through the extensive use of electronic tools such as web hosted meetings, voice teleconferences and various secure data exchange tools.
- Second, after completion of a thorough review of program progress and the supporting statutory and regulatory requirements, Dr. William B. Roper, Assistant Secretary of the Air Force for Acquisition, Technology & Logistics, granted Milestone B certification and WSF-M program approval on May 15.
- The certification formally baselines the program execution requirements, including the establishment of cost and schedule caps, that will govern the program through launch and handover of the capability to operations.
- Lt. Col. Wilfredo Ruiz, WSF-M program manager said that he is fortunate to have a dedicated team committed to providing capability on time, no matter what the obstacle.
- These accomplishments demonstrate SMC’s commitment in the face of challenges to rapidly deliver Space-Based Environmental Monitoring capabilities to the warfighter. The WSF-M program is executed by the SMC Production Corps, whose mission is to continue forging the future of space by delivering next generation capabilities to our warfighters and mission partners in front of the need. The Production Corps’ agile program management techniques, smart business approach and close teaming with industry and Department of Defense stakeholders are enabling the production of advanced space-based systems to enhance warfighting weather prediction and analysis capabilities.
- WSF-M is the next generation of space based passive microwave sensing technology, and will provide U.S. and Allied warfighters with essential weather data including the measurement of ocean surface wind speed and direction; ice thickness; snow depth; soil moisture; and local spacecraft energetic charged particle environment. The ocean surface wind speed measurement enables tropical cyclone intensity determination by the Joint Typhoon Warning Center. The data gathered by WSF-M will be provided to meteorologists in support of the generation of a wide variety of weather products necessary to conduct mission planning and operations globally every day.
- The Space and Missile Systems Center is the U.S. Space Force's center of excellence for acquiring and developing military space systems. SMC’s portfolio includes space launch, global positioning, military space vehicle communications, defense meteorological space vehicles, range systems, space vehicle control networks, space-based infrared systems, and space situational awareness capabilities.
• April 20, 2020: Ball Aerospace conducted a critical design review (CDR) of the Weather System Follow-on (WSF-M) satellite mission, which it is building for the U.S. Space Force (USSF) Space and Missile Systems Center (SMC). 3)
- With CDR concluded, Ball Aerospace begins full production of the satellite. Upon delivery, this next-generation operational environmental satellite system will provide critical and actionable environmental intelligence to military operations in all warfighting domains.
- “Measuring and understanding the physical environment is critical to military operations, from determining tropical cyclone intensity for asset protection and maneuver operations to how wind and sea state play into assured access and aircraft carrier operations,” said Mark Healy, vice president and general manager, National Defense, Ball Aerospace. “Ball is proud to be a mission partner with the Space Force, working closely and collaboratively to ensure the success of this program, which extends Ball’s legacy of providing precise measurements from space to enable more accurate atmospheric and ocean forecasting.”
- The Weather System Follow-on (WSF) mission is designed specifically to mitigate three high-priority Department of Defense (DoD) Space-Based Environmental Monitoring (SBEM) gaps: ocean surface vector winds, tropical cyclone intensity and the space weather gap, low Earth orbit (LEO) energetic charged particles. It will also address three additional SBEM gaps: sea ice characterization, soil moisture and snow depth. As the prime contractor for WSF, Ball is responsible for delivering the entire mission, including instrument, spacecraft and system software, as well as the algorithms for data products, to SMC.
- This new environmental satellite system leverages the Ball-built Global Precipitation Measurement (GPM) Microwave Imager (GMI) instrument, which is the on-orbit reference standard for calibrating precipitation measurements in NASA’s GPM constellation. The WSF-M bus will be based on the Ball Configurable Platform, a proven, agile spacecraft with 50 years of on-orbit operations for affordable remote sensing applications.
- Ball has also played key roles on numerous operational weather satellite programs, including the Ball-built Suomi National Polar-orbiting Partnership (Suomi NPP) satellite, which launched in 2011, and the Joint Polar Satellite System-1 (JPSS-1) satellite, now NOAA-20, which launched in 2017.
• February 20, 2020: On Feb. 11, after more than 22 years of providing vital global weather data to the U.S. and its allies, Defense Meteorological Satellite Program (DMSP) Flight 14 was decommissioned after completing 118,052 orbits of the Earth. End of Life (EOL) procedures were accomplished by operators at the National Oceanic and Atmospheric Administration (NOAA) Satellite Operations Facility (NSOF) in Suitland, Maryland, under the direction of United States Space Force’s 50th Space Wing. Space and Missiles Systems Center technical experts worked in concert with the rest of the team to ensure the EOL procedures were effectively and efficiently executed. 4)
- The remaining four operational DMSP satellites continue to provide a resilient capability for collecting and disseminating global environmental data in support of operations around the world. The DMSP satellites continue to be sustained past their original three- to five-year design life. At the time of its decommissioning, F-14 was in operations for more than 22 years. According to the program office, the longevity of DMSP is a testament to the work of each and every person that has been a part of the program, and to the multi-agency partnerships that have been fostered since the beginning of DMSP.
- SMC remains at the forefront of providing the next generation of modernized space based environmental monitoring capabilities, ensuring the critical weather mission will continue in the future. The Weather System Follow-on – Microwave (WSF-M) program will be holding its critical design review the week of March 31. WSF-M satellites will provide the next generation passive microwave sensing capability that provides ocean surface wind speed and direction measurements, supports tropical cyclone intensity prediction, and will also host an energetic charged particle sensor for measurement of the local space environment. The first WSF-M satellite is expected to be operational in Fiscal Year 2024.
- The U.S Space Force’s Space and Missile Systems Center, located at Los Angeles Air Force Base in El Segundo, California, is the Center of Excellence for acquiring and developing military space systems. Its portfolio includes the Global Positioning System, military satellite communications, defense meteorological satellites, space launch, range systems, satellite control networks, space-based infrared systems and space situational awareness capabilities
• November 29, 2017: Ball Aerospace has been selected by the U.S. Air Force's Space and Missile Systems Center (SMC) to deliver the next-generation operational environmental satellite system, Weather System Follow-on – Microwave (WSF-M), for the Department of Defense (DoD). WSF-M is a predominantly fixed price contract that will provide for system design and risk reduction of a Low Earth Orbit (LEO) satellite with a passive microwave imaging radiometer instrument and hosted Government furnished energetic charged particle (ECP) sensor. The contract will include options for the development and fabrication of two LEO satellites as well as options for launch vehicle integration, launch and early orbit test, and operational test and evaluation support. This mission will improve weather forecasting over maritime regions by taking global measurements of the atmosphere and ocean surface. 5)
- WSF-M is designed to mitigate three high priority DoD Space-Based Environmental Monitoring (SBEM) gaps: ocean surface vector winds, tropical cyclone intensity and LEO energetic charged particles.
Ball Aerospace (Ball) is under a contract with the Air Force Space and Missile Systems Center (SMC) in El Segundo, CA, to provide the Weather System Follow-on – Microwave (WSF-M) Mission. As Mission Prime, Ball is responsible for delivering Environmental Data Record (EDR)-level performance for Ocean Surface Vector Winds (OSVW), Tropical Cyclone Intensity (TCI), Soil Moisture, Snow Depth, and Sea Ice Characterization, as well as providing Imagery products. The Ball WSF-M mission design provides the next-generation environmental satellite system for the Department of Defense (DoD) following the successes of Ball’s civil weather systems: Suomi National Polar-orbiting Partnership (Suomi NPP), Joint Polar Satellite System (JPSS)-1, and the Global Precipitation Measurement (GPM) Microwave Imager (GMI) sensor. This paper presents an overview of the mission, the predicted performance, provides details on the instrument and spacecraft design, planned hardware demonstrations, and gives current status. 6)
Mission overview: WSF-M is a DoD (Department of Defense) operational, low earth orbit (LEO), environmental satellite system that provides continuous space-based sensing of the terrestrial environment. Terrestrial sensing is currently provided by the Defense Meteorological Satellite Program (DMSP) and WindSat. The Space Segment consists of a LEO spacecraft bus and two payloads. The primary payload is a Microwave Imager (MWI) sensor that takes calibrated passive radiometric measurements at multiple microwave frequencies to enable derivation of Ocean Surface Vector Winds (OSVW), Tropical Cyclone Intensity (TCI) and additional EDRs. In addition, the government-provided Energetic Charged Particle (ECP) sensor provides in-situ space weather measurements to enable derivation of ECP flux and warnings. Both payloads provide sensor data to the spacecraft for combination with spacecraft telemetry to form the mission data which is downlinked to the ground system.
Mission data is downlinked to the Air Force Satellite Control Network (AFSCN) for routing to the Enterprise Ground Services (EGS) Data Operations Center where it is processed to separate the MWI and ECP data. The microwave instrument mission data is distributed to the Air Force’s Air Combat Command (ACC) 557th Weather Wing (WW), and to the Fleet Numerical Meteorology and Oceanography Center (FNMOC). The weather centrals use the Ball developed algorithms to process the mission data into Temperature Data Record (TDR), Sensor Data Records (SDR) and EDR products meeting the required performance. The EGS Operations Center processes the raw ECP data into products that support host satellite anomaly resolution, and state of health trending and analysis.
In addition, WSF-M broadcasts Real-Time Data (RTD), including all ancillary data needed to process the real-time data, directly to equipped Department of Defense (DoD) direct readout sites that use the Ball-developed algorithms to produce EDR mission products. Space vehicle telemetry is downlinked from the spacecraft and relayed to the EGS Operations Center where they are used to monitor spacecraft and instrument status. Mission Telemetry, Tracking & Command (TT&C) Services are provided by the ground system.
Performance overview: Ball derives the MWI sensor requirements from the WSF-M Technical Requirements Document (TRD) through an end-to-end (E2E) simulation that includes surface and atmospheric models, sensor characteristics, calibration uncertainty, and EDR retrieval algorithms. The WSF-M EDRs require that the sensor include the channel set shown in Table 1. Ball has selected a Sun-synchronized 833 km orbit for the WSF-M space vehicle (SV) to meet the swath width and refresh rate requirements. For the selected WSF-M orbit, the MWI antenna provides the required horizontal resolution of less than 30 km for the 10 GHz channel, consistent with current WindSat performance.
Ball’s WSF-M design meets all OSVW, TCI, and Imagery SDR requirements with margin. Predicted performance for OSVW across the wind speed range of 5 to 25 m/s is shown in Figure 1. Ball’s E2E simulation generates MWI-measured scenes consistent with WindSat data and includes all significant error sources. The simulation’s Noise Equivalent Delta Temperature (NEDT) and calibration uncertainty are based on GMI-verified on-orbit performance providing high confidence in these values. Polarimetric parameters are based on measured performance of prototype polarimetric receiver hardware. These simulated MWI-measured scenes are input into the operational retrieval algorithms and the retrieved OSVW product compared to the input scene. The operational retrieval algorithms are provided by Ball partners Remote Sensing Systems (RSS) and Atmospheric and Environmental Research (AER).
Figure 1: Speed and wind direction uncertainty. Predictions from the mature validated E2E model show a minimum of 20% margin on wind direction and a minimum of 70% margin on wind speed for each 2 m/s wind speed bin (image credit: Ball Aerospace)
Space vehicle overview: The notional WSF-M Space Vehicle is shown in Figure 2. The WSF-M spacecraft is based on the BCP (Ball Configurable Platform) product line, a stable, agile, high-throughput spacecraft designed specifically for long-lived, remote-sensing missions like WSF-M. We have designed, built, and delivered ten BCP space vehicles and WSF-M joins three more SVs in development in our production line. Recent BCP examples include five commercial high-resolution satellite systems, Suomi-NPP, JPSS-1, and ICESat. The ECP is shown in the deployed configuration.
Launch: A launch of the WSF-M satellite is expected in 2023, providing operational services in 2024.
Orbit: Sunsynchronous orbit, LEO.
Sensor complement (MWI, ECP)
MWI (Microwave Imager)
The MWI requirements and design have been derived by Ball to meet the required EDR performance and leverage the heritage design features of the GMI Instrument that was built and tested by Ball for NASA (National Aeronautics and Space Administration). The GMI instrument was launched onboard the GPM (Global Precipitation Measurement) spacecraft on February 28th, 2014 and has operated continuously since then completing over 5 years of successful operation on-orbit. The flow down of WSF-M EDR requirements to MWI resulted in a set of requirements that is similar to GMI – providing a low-risk design foundation for the MWI.
The MWI instrument is shown in Figure 2. The MWI is a conically scanning polarimetric microwave radiometer with channels from 10 GHz to 89 GHz. Detailed characteristics for each of the 17 channels on MWI are shown in Table 1. These channels map closely to the GMI channel set, providing significant heritage in the receiver subsystem. 7)
Table 1: Channel characteristics and performance. The channel set for the Ball MWI includes the 10.85 to 89 GHz imaging channels with digital full Stokes outputs for 10.85, 18.85 and 36.5 GHz. (The subscripts “d” and “a” denote the digital and analog outputs of the 37 GHz receiver, respectively)
The MWI utilizes 3rd and 4th Stokes sensitivity to wind direction on the 10, 18, and 37 GHz bands to measure OSVW (Ocean Surface Vector Winds). 8) The MWI produces the 3rd and 4th Stokes polarimetric channels by digitally sampling and cross-correlating v-pol and h-pol amplitude signals. Digital polarimetry has the major advantages of reduced complexity and better calibration performance than analog designs. 9)
The 10, 18, and 36 GHz channels are fully polarimetric providing the V, H, 3rd and 4th Stokes. The designs of these polarimetric channels optimizes the use of the heritage GMI designs while incorporating the needed polarimetric capability. The RF front ends include phase-matched v-pol and h-pol channels based on the heritage GMI design. The analog outputs of the front end are down converted to an intermediate frequency enabling sampling by a high-speed analog-to-digital converter and processing by the digital backend. A digital processor directly computes the complex correlation between the v-pol and h-pol channels, yielding the 3rd and 4th Stokes parameters essential to OSVW retrievals. This digital-receiver-based approach for polarimetric channels has been proven on the NASA SMAP mission where the digital polarimetric capability has been used for ionospheric correction and for OSVW retrieval in hurricanes .10) The receiver subsystem built by ITT Exelis provides low noise figures and very good stability for excellent radiometric performance.
The Antenna Subsystem consists of the 1.8-m Main Reflector (MR), four separate feed horns, and calibration targets. The Reflector Deployment Assembly (RDA) stows the MR and deploys it to the on-orbit configuration. This stowage gives the instrument a relatively compact stowed size given the 1.8- meter aperture size. The Spin Mechanism Assembly serves multiple functions; including conical scanning, signal transfer and power distribution through internal slip rings. The MWI Spin Mechanism Assembly is a build-to-print copy of the GMI SMA which has demonstrated over 5 years of onorbit performance without any anomalies. The SMA also has significant heritage to the WindSat Bearing and Power Transfer Assembly (BAPTA) which has operated for over 15 years. The Instrument Controller Electronics (ICE) subsystem provides the interface to the spacecraft and is responsible for MWI control.
Ball designed the MWI with multiple features proven on GMI to provide excellent calibration accuracy and provide the most accurate, precise and consistent data possible. 11) These features include proven VDA reflector coating technology that eliminates calibration errors from antenna emissions. Noise diodes on the 10-37 GHz channels provide on-orbit trending of non-linearity and backup gain calibration used in on-orbit calibration/validation activities to significantly improve GMI radiometric stability . 12) Also, tight hot load shrouding eliminates solar intrusion into the hot load.
Accurate, stable radiometric calibration of the Stokes parameters is essential to the on-orbit polarimetric receiver performance. The 3rd and 4th Stokes on-orbit calibration is performed via a Correlated Noise Source (CNS) included at the input of each receiver front end. The CNS employs stable heritage noise diodes used for the operational GMI payload that, together with a simple combining network, inject correlated calibration signals into the receiver front end.
Planned hardware demonstrations: Prototype hardware is being developed in four areas: (1) RF Digital Polarimetric Receivers, (2) Main Reflector, (3) Reflector Deployment Assembly, and (4) Instrument Controller Electronics.
Ball’s partner Harris (EDO) is building the 37 GHz MWI polarimetric correlated noise source and down-converter assembly prototypes. This is combined with the Ball-built prototype Digital Receiver Assembly (DRA) and existing 37 GHz receivers from GMI to provide an end-to-end receiver at 37 GHz. The RF receiver includes a prototype of the electronics and digital controller board that incorporates redundancy and adds electrical interface capability to the Digital Polarimetric Receiver Assemblies.
Ball’s Reflector Deployment Assembly partner, Northrop Grumman (Orbital ATK), builds and tests the MWI RDA prototype scaled in size from the GMI RDA. Ball’s Main Reflector partner, AASC, builds and tests a MWI 1.8-m MR prototype scaled in size from the GMI 1.2-m MR. Following completion of subsystem testing, the MR and RDA are integrated and tested. Finally, Ball builds and tests the MWI Instrument Controller Electronics (ICE) prototype.
ECP (Energetic Charged Particle) Sensor
The ECPs are hosted government furnished instruments. The U.S. Air Force intends to include ECP sensors on all future satellites for space weather monitoring, starting from the early 2020s. The USAF awarded contracts to Applied Technology Associates and Teledyne Brown Engineering to manufacture satellite instruments to detect Energetic Charged Particles (ECPs). 13)
The Air Force awarded a $5 million contract to Applied Technology Associates of Paso Robles, California, to assemble a sensor developed by the Air Force Research Laboratory. The sensor, Compact Environmental Anomaly Sensor 3, includes two particle telescopes to “provide a comprehensive measure of the space environment,” Capt. Kaitlin Toner, Air Force Space and Missile Systems Command spokeswoman, said in an emailed response to SpaceNews questions.
The Air Force also awarded a $1.8 million contract to Teledyne Brown Engineering of Huntsville, Alabama, to assemble ECP-Lite, a sensor developed by the Aerospace Corp. “ECP-Lite is a low size, weight and power sensor that will provide a focused subset of space environmental data,” Toner said.
The contracts are part of the Air Force’s effort to improve space weather monitoring. Air Force Secretary Deborah Lee James issued a memo in 2015 calling for ECP sensors on all new Air Force satellites.
The sensors built by Applied Technology Associates and Teledyne Brown Engineering are scheduled to be launched on different spacecraft in late 2020 and early 2021, Toner said. “Testing will occur within 12 months of launch,” she added.
Debra Werner,”Air Force to bolster weather capabilities with
small satellites and sensors,” SpaceNews, 11 January 2018, URL: https://spacenews.com
2) ”Despite Numerous Challenges, the Weather System Follow-on Microwave Program Passes Two Milestones,” Satnews Daily, 18 May 2020, URL: http://www.satnews.com/story.php?number=1412828539
”Ball Aerospace Conducts Critical Design Review for U.S. Space
Force’s WSF Next-Gen Weather Satellite,” Ball Aerospace, 20
April 2020, URL: https://defpost.com
”DMSP satellite decommissioned after 22 years of service, Weather
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Review in March,” SMC Public Affairs, Space and Missile Systems
Center, 20 February 2020, URL: https://www.losangeles.af.mil/News/Article-Display/Article
5) ”Ball Aerospace Wins Major U.S. Air Force Contract for Next-Gen Weather Satellite,” Ball Aerospace News Release, 29 November 2017, URL: http://www.ball.com/aerospace/newsroom/detail?newsid=123879
6) David Newell, David Draper, Quinn Remund, Brian Woods, Catrina Mays, Bill Bensler, Dan Miller, Ken Eastman, ”Weather Satellite Follow-On – Microwave (WSF-M) Design And Predicted Performance,” AMS (American Meteorological Society), 20th Symposium on Meteorological Observation and Instrumentation, Boston, MA, USA, 13-16 January 2020, URL: https://ams.confex.com/ams/2020Annual/webprogram/Paper369912.html
7) David Newell, David Draper, Don Figgins, Barry Berdanier, Michael Kubitschek, David HolshouserAdam Sexton, Sergey Krimchansky,Frank Wentz, and Thomas Meissner, ”GPM microwave imager key performance and calibration results,” Proceedings of IGARSS 2014, pp 3754 –3757, 2014
9) J. R. Piepmeier ; A. J. Gasiewski, ”Digital correlation microwave polarimetry: analysis and demonstration,” IEEE Transactions on Geoscience and Remote Sensing, Volume: 39 , Issue: 11 , November 2001
10) Simon H. Yueh, Alexander G. Fore, Wenqing Tang, Akiko Hayashi, Bryan Stiles, Nicolas Reul, Yonghui Weng, Fuqing Zhang, ”SMAP L-Band Passive Microwave Observations of Ocean Surface Wind During Severe Storms,” IEEE Transactions on Geoscience and Remote Sensing, Volume 54 , Issue 12 , Dec. 2016, pp: 7339 - 7350
Frank J. Wentz, David Draper, ”On-orbit absolute calibration of
the Global Precipitation Mission Microwave Imager,” AMS, July
2016, URL: https://journals.ametsoc.org
12) David W. Draper, David A. Newell, Darren S. McKague, Jeffrey R. Piepmeier, ”Assessing Calibration Stability Using the Global Precipitation Measurement (GPM) Microwave Imager (GMI) Noise Diodes,” IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, Volume 8 , Issue 9 , Sept. 2015
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 (firstname.lastname@example.org).