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
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)
Figure 8: The field terminal architecture of the NPP / NPOESS satellites (image credit: NASA, NOAA, IPO)
• 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 May 2021, the previously large SuomiNPP file has been split into three 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 2021
Mission status and some imagery in the period 2021
- According to Sakha’s emergencies ministry, more than 250 fires were burning across roughly 5720 km2 (2,210 square miles) of land on July 5—an area about twice the size of Luxembourg. While regional authorities report extinguishing dozens of fires per day, they call the situation “difficult” and will likely be battling large fires for weeks. Thick smoke has occasionally enveloped Yakutsk, the largest city (population 312,000) in Sakha, and other settlements in the region.
Figure 10: Large, smoky fires are raging through forests in northeastern Russia. The VIIRS (Visible Infrared Imaging Radiometer Suite) on Suomi NPP acquired this natural-color image of large clouds of smoke enveloping the Republic of Sakha (Yakutia) on July 5, 2021. Satellite data indicates that several small fires burned intermittently in the area for weeks, but several exploded in size during the last week of June (image credit: NASA Earth Observatory images by Lauren Dauphin, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview and Landsat data from the U.S. Geological Survey. Story by Adam Voiland)
Figure 11: This image, acquired by the MODIS instrument on NASA's Aqua satellite, shows more distinct plumes from five large fires burning around Penzhina Bay (northwest of the Kamchatka Peninsula), image credit: NASA Earth Observatory.
- This is the second consecutive July that intense heat and wildfires have ravaged this region. In 2020, fires raged in Yakutia for much of July and August. Siberia wildlands also burned extensively in 2001, 2005, and 2013, according to a summary of the 2020 Siberian fire season authored by researchers from George Mason University and Siberian Federal University. An international group of scientists recently published a study noting that the prolonged heat waves in Siberia in 2020 would have been "almost impossible" without the influence of human-induced climate change.
Figure 12: This image, from the Operational Land Imager (OLI) on Landsat-8, shows a detailed view of one of the fires on July 4 (image credit: NASA Earth Observatory)
• June 8, 2021: The millions of tons of dust lofted out of northwest Africa each year are a visual reminder of how Earth’s systems are interconnected. Dust blowing out of the Sahara fertilizes the surface waters of the Atlantic and the soils of the Americas. It influences the development of hurricanes and other weather systems. The airborne particles reflect and block sunlight, affecting the planet’s radiation budget. In heavy doses near the ground, dust plumes can hamper air quality, harm breathing, and reduce visibility. 27)
Figure 13: The millions of tons of dust lofted out of Africa each year are a visual reminder of how Earth’s systems are interconnected. In early June 2021, strong winds blew across Mali and Mauritania and carried tiny bits of the Sahara over Senegal, The Gambia, and Cabo Verde. The Visible Infrared Imaging Radiometer Suite (VIIRS) on the NASA-NOAA Suomi NPP satellite acquired this natural-color image on June 4, 2021, the first day of the storm. As this time-lapse shows, dust was well out over the central Atlantic Ocean by June 7 (image credit: NASA Earth Observatory image by Joshua Stevens, using VIIRS data from NASA EOSDIS LANCE, GIBS/Worldview, and the Suomi National Polar-orbiting Partnership. Story by Michael Carlowicz)
- The storm comes roughly one year after NASA instruments chronicled the largest dust storm in two decades of observations. Saharan dust shrouded the Caribbean Sea in June 2020 and even dimmed skies over several states of the U.S. Southeast. Satellite and ground sensors measured the highest concentration of dust in the atmosphere since NASA’s Earth Observing System satellites were launched.
- Researchers from the University of Kansas used data from NASA’s Terra and Aqua satellites, Suomi NPP, the joint NASA-CNES CALIPSO satellite, and ground stations to delineate how adjacent atmospheric circulation patterns can shepherd dust across such vast distances. “The African easterly jet [stream] exports the dust from Africa towards the Atlantic region” said lead author Bing Pu. “Then the North Atlantic subtropical high, which is a high-pressure system sitting over the subtropical North Atlantic, can further transport it towards the Caribbean region. The Caribbean low-level jet, along with the subtropical high, can further transport the dust from the Caribbean region towards the States.”
Figure 14: Every year millions of tons of dust from the Sahara Desert are swirled up into the atmosphere by easterly trade winds, and carried across the Atlantic. The plumes can make their way from the African continent as far as the Amazon rainforest, where they fertilize plant life. - As the climate changes, dust activity will continue to be affected. In a new study, NASA researchers predict that within the next century we will see dust transport approach a 20,000-year minimum (video credit: NASA/GSFC/Scientific Visualization Studio)
- Several recent studies have offered differing ideas about the future of African dust storms and transport. Pu and colleagues assert that dust storms are likely to grow more intense and frequent with climate change. Higher temperatures would bring more drying and less vegetation to the region, providing more loose, dusty material to be picked up from Africa. Stronger storms and winds in a warming world could provide more energy to carry that dust.
- On the other hand, a research team led by atmospheric scientist Tianle Yuan of NASA’s Goddard Space Flight Center used a combination of satellite data and computer models to predict that Africa’s annual dust plumes might actually shrink over the next century to a 20,000-year minimum. They argue that changes in ocean temperatures could reduce prevailing wind speeds and thus the transport from Africa to the Americas. They also note that the wind changes could influence the amount of moisture flowing into Africa, leading to more rainfall and vegetation in dusty Saharan and Sub-Saharan regions. They assert that global warming could bring a 30 percent reduction in Saharan dust activity over the next 20 to 50 years and a continued decline beyond that.
• May 18, 2021: An unusually powerful tropical cyclone named Tauktae struck the Indian state of Gujarat on May 17, 2021. The Visible Infrared Imaging Radiometer Suite (VIIRS) on the NASA-NOAA Suomi NPP satellite acquired this natural-color image of the storm a few hours before it made landfall between Porbandar and Mahuva. 28)
- Even before making landfall, Tauktae caused a trail of destruction in Kerala, Karnataka, Goa, and Maharashtra as it brushed India’s northwest coast over the weekend. According to news reports, the storm contributed to the deaths of at least 12 people, destroyed hundreds of homes, and caused power outages and traffic jams. More than 150,000 people evacuated Gujarat in anticipation of Tauktae’s arrival.
- The North Indian Ocean generates only about 7 percent of the world’s tropical cyclones, but storms can be quite devastating when they occur because of the large number of people who live along low-lying coastlines. Compared to the Bengal Sea to the east, cyclones are uncommon in the Arabian Sea, an area that typically sees one or two storms per year. Cool water temperatures, dry air, and unfavorable upper-level winds typically make storms in the Arabian Sea weak and short-lived, though powerful storms occasionally come together under the right environmental conditions.
- In Tauktae’s case, conditions were ideal. Upper-level winds were calm and conducive to storm formation. Sea surface temperatures in the Arabian Sea were about 31° Celsius (88° Fahrenheit) as the storm approached Gujarat, a few degrees warmer than usual for mid-May. A rule of thumb among scientists is that ocean temperatures should be above 27° C to sustain a tropical cyclone.
Figure 15: Tropical cyclones are scarce in the Arabian Sea, but unusually warm ocean temperatures helped fuel this storm. As Tauktae approached land, the U.S. Joint Typhoon Warning Center reported maximum sustained winds of 100 knots (185 km/125 miles per hour) and gusts up to 125 knots (230 km/145 miles), equivalent to a category 3 or 4 hurricane. That made Tauktae the fifth-strongest storm observed in the Arabian Sea since 1998. Winds of that strength can easily snap trees, topple power lines, and damage homes. The storm also pushed a destructive storm surge of water onto the Indian coast; reports suggest it may have been as high as 3 meters in some areas (image credit: NASA Earth Observatory image by Lauren Dauphin, using VIIRS data from NASA EOSDIS LANCE, GIBS/Worldview, and the Suomi National Polar-orbiting Partnership. Story by Adam Voiland)
- During the past few decades, a group of NOAA researchers have observed an increase in the intensity of tropical cyclones in the Arabian Sea, particularly in the post-monsoon season. The group’s modeling results indicate that global warming and rising ocean temperatures are among the reasons for the change.
• May 17, 2021: Satellite views of Earth at night have proven useful for disaster response and recovery, for detection of population changes and urban development, for studies of energy consumption, and many other uses. Since the 2011 launch of the NOAA-NASA Suomi NPP satellite—as night light data have become freely available to scientists and the public within hours of acquisition—the applications have proliferated. 29)
- Ocean conservation researchers have found another use for nighttime imagery: tracking unregulated, under-reported, and sometimes illegal fishing. When combined with commercial fishing reports and ship identification systems, night light data have revealed patterns of deep-sea fishing that may be unsustainable for ecosystems and detrimental to countries with less advanced fishing fleets. In the Indian Ocean alone, the UN Food and Agriculture Organization (FAO) estimates that 30 percent of assessed fish stocks are being fished beyond sustainable limits.
- The nighttime image of Figure 16 was acquired on February 15, 2021, by the VIIRS (Visible Infrared Imaging Radiometer Suite) on Suomi-NPP. VIIRS has a specially designed day-night band that detects nighttime light in a range of wavelengths from green to near-infrared and uses filtering techniques to observe signals such as city lights, reflected moonlight, and fishing boats. A second VIIRS instrument flies on the NOAA-20 satellite.
Figure 16: Researchers have found another use for night lights imagery: tracking unregulated and under-reported fishing. In this image, points of light in the Arabian Sea (northwest Indian Ocean) indicate the locations of fishing boats, refrigerated cargo ships, and perhaps a few other large ships. The fishing boats stand out because they use high-intensity lights to draw squid, saury, and other fish toward the water surface, where they are more easily caught with jigging lines and purse seine nets. Squid boats can carry more than a hundred lamps and generate as much as light as a house (image credit: NASA Earth Observatory images by Lauren Dauphin, using VIIRS day-night band data from the Suomi NPP satellite and AIS-based fishing effort and vessel presence data from Global Fishing Watch, story by Michael Carlowicz)
Figure 17: This photo shows fishing boats lighting up the horizon of the Arabian Sea in April 2021 (courtesy of Trygg Mat Tracking)
- “It’s a gold rush out there,” said Joaquim Goes, a marine ecologist at Lamont Doherty Earth Observatory. “The area is rich in squid, and it is just outside of the exclusive economic zones of Oman, Yemen, India, and Pakistan.”
- Fishing in this part of the northwest Indian Ocean has expanded every year since 2015, according to a 2020 report by Trygg Mat Tracking, the World Wildlife Fund, and Global Fishing Watch (GFW). At first, boats were mostly observed from November through January; the fleets now show up regularly from September to May. Most vessels stay out of the region during monsoon season. Overall, the number of fishing vessels regularly working this area increased from about 30 in 2015 to nearly 300 by 2019. (GFW has created an animation of the Arabian Sea fleet pattern.)
- While the fishing here is not illegal, it is unregulated, and ocean conservation groups and the FAO are concerned about sustainability and equity. The squid catch is used for both direct human consumption and for fish meal for the aquaculture industry. Squid and saury are also prey for tuna, swordfish, and other species in the Indian Ocean, and it is unclear how those fisheries are affected by squid harvesting. The equity questions arise from the use of high-tech equipment by some foreign vessels when such gear is not affordable or allowed by developing nations in Africa and southwest Asia that rely on these fisheries for food security and economic health.
- As global demand for seafood continues to rise, it becomes ever more important to have a clear view of ocean activities and their potential consequences, noted Duncan Copeland, executive director of Trygg Mat Tracking, a nonprofit institute that monitors fishing. “We face destabilizing both marine ecosystems and the marine resources that many people depend on for income and food security,” he said.
- Since AIS data are publicly available, GFW and other groups used it to track global ship movements from port to sea and back. They employed machine learning to analyze more than 30 billion AIS messages and identify shipping patterns. For instance, the data mining revealed the use of refrigerated cargo vessels, which transfer the fishing catch from smaller boats and transport it back to port while the fishermen continue to work offshore for weeks to months. According to GFW, “Only a small proportion of the world's approximately 2.9 million fishing vessels are equipped with the AIS system, but they are responsible for a disproportionate share of the fish caught.”
- AIS signals alone cannot capture the full scale of industrial fishing. Signal interference and faulty equipment can distort ship numbers; other times, fishing boats turn off the beacons in order to avoid pirates or fishing enforcement agencies. This is where night light detection can reveal what official systems might not detect. The map above, derived from Global Fishing Watch data, shows ships detected by AIS beacons in orange and those detected by VIIRS day-night band in blue.
- “Worldwide, the VIIRS instruments are detecting 10,000 to 20,000 boats every night that are not broadcasting AIS or VMS. By detecting the signal from lights present on fishing vessels we can calculate a better estimate of the size of certain fleets,” said Chris Elvidge, who developed VIIRS boat-detection tools while working for NOAA. Elvidge and colleagues at GFW found that more than 85 percent of their VIIRS detections came from vessels that lacked AIS or VMS.
- “VIIRS supports our AIS and VMS data, and it complements other imagery sources like synthetic aperture radar and optical imagery,” said Nate Miller, senior data scientist at GFW. “Each of these technologies has strengths and limitations, but by combining them we are able to create a more complete picture of fishing.”
Figure 18: Vessel tracking starts with Automatic Identification System (AIS) transponders, which are designed to prevent collisions at sea by constantly transmitting a ship's location, and vessel monitoring systems (VMS), which are designed for fisheries monitoring and surveillance. The International Maritime Organization has mandated that all ships larger than 300 gross tons must use the AIS system while traveling internationally. The signals are collected by satellite and broadcast to mariners and shipping agencies. This image was acquired on 17 December 2020 with VIIRS and annotated with AIS fishing detections (image credit: NASA Earth Observatory)
• On April 11, 2021, a category three storm made a rare landfall in Western Australia, causing significant damage to coastal towns that are mostly ill-equipped for cyclones. Tropical Cyclone Seroja tore through 1,000 km (600 miles) of land, knocking down trees and damaging buildings along its southward path. At least 15,000 homes lost power. Seroja has since weakened and moved offshore, but government agencies are now dealing with the damage. 30)
- Kalbarri, a resort town of around 1,500 people, received the brunt of the storm’s force. Seroja made landfall just south of Kalbarri on the evening of the 11th and damaged about 70 percent of the town’s structures, according to news reports. Wind gusts clocked in at 170 kilometers (100 miles) per hour—likely the strongest winds in the area in more than 50 years. Overnight, Kalbarri received around 167 mm (6.6 inches) of rain.
- Seroja continued southeast and caused damage in the city of Geraldton, too. Downgraded to a category two storm at the time, Seroja was the first storm of that intensity to hit Geraldton in more than 50 years. The storm was further downgraded on April 12th as it moved across the Wheat Belt, located in the southwest corner of Australia.
Figure 19: The category three cyclone made a rare landfall in Western Australia, causing significant damage to coastal towns. The VIIRS instrument on the Suomi NPP satellite captured this image on April 11, hours before the storm made landfall (image credit: NASA Earth Observatory image by Joshua Stevens, using VIIRS data from NASA EOSDIS LANCE, GIBS/Worldview, and the Suomi National Polar-orbiting Partnership. Story by Kasha Patel)
- Seroja’s southward trajectory is unusual; scientists estimate that cyclones of this intensity have only traveled this far south 26 times in the past 5,000 years. However, Seroja curved south when it interacted with a different tropical system earlier in the week. This clash—a rare phenomenon known as the Fujiwhara Effect—caused the systems to rotate around one another and launched Seroja towards the west. Seroja intensified due to warmer-than-normal sea surface temperatures influenced by La Niña conditions. Winds kept Seroja away from the coast and the weakened effects of land, allowing the cyclone to sustain relatively high intensity.
- Before entering Australian waters, Seroja had already caused significant damage to Indonesia. Seroja, which made landfall there on April 5, caused flash flooding and landslides. More than 160 people were killed and 22,000 people have been displaced. The storm was the strongest tropical cyclone to hit Indonesian land since 2008.
• March 22, 2021: As of 2019, about 700 million people around the world lived without electricity at home. More than three-quarters of those people lived in sub-Saharan Africa. Among those African households with electricity, only a fraction have enough reliable power to run refrigerators or stoves, let alone computers or agricultural equipment. 31)
- “In order to build infrastructure to reach communities without electricity, one needs a clear understanding of where these populations are, how large they are, and how sparse the communities are,” said Giacomo Falchetta, an energy researcher at the non-profit Fondazione Eni Enrico Mattei (FEEM) in Italy. “This information on a province level is not readily available even to national authorities.”
- Using satellite data, Falchetta and his colleagues from the International Institute for Applied Systems Analysis (IIASA) developed a new way to estimate the number of people without electricity across sub-Saharan Africa. This information is being shared with the public via a web-based interface and the UN Sustainable Development Solutions Network, which includes more than 1,400 organizations working towards providing affordable, reliable, sustainable, and modern energy.
Figure 20: The maps of Figures 10, 21 and 22 show the team’s electrification analysis for 2018 around Lake Victoria, in Ethiopia, and across sub-Saharan Africa, respectively. The maps were created using processed nighttime light data—namely public lighting and, partly, house lighting—from the Visible Infrared Imaging Radiometer Suite (VIIRS) on the NOAA-NASA Suomi NPP satellite. The team also incorporated land cover type data from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) to identify urban and rural settlements. Those datasets were overlaid with different gridded population products, such as the 1 km (0.60-mile) scale data from Oak Ridge National Laboratory’s LandScan to better understand how populations are distributed (image credit: NASA Earth Observatory images by Lauren Dauphin, using data from Falchetta, Giacomo, et al. (2019) and Falchetta, Giacomo, et al. (2020). Story by Kasha Patel)
- In working on these electricity access maps since 2014, the team has found several trends. The map below shows the pace of electrification from 2014-2019 in relation to a province’s population growth. Population changes are important because the growth can outpace the rate of electrification, leading to less people with access to electricity. Shades of red depict areas where electrification was slower than the population growth. Blue areas show locations where electrification grew faster than the population, leading to better electricity access.
- From 2014 to 2019, they estimated more than 115 million people gained electricity across the region. The majority of these electricity gains occurred in urban areas and in countries in western and southern Africa with stable governments that could procure new electricity connections. These countries also had relatively smaller growth in their populations, allowing countries to set up sufficient electrical systems to the current populations. Several countries, such as Ghana and South Africa, are on a pathway to full electrification in upcoming years.
- However, the team found that electricity access declined in some rural places from 2014-2019. Collectively Ethiopia, Nigeria, and the Democratic Republic of the Congo had 231 million people without access to electricity—40 percent of people off the grid across the continent. Many of the electricity deficits were occurring in countries with rapid population growth, which exacerbated the challenge and slowed the rate at which countries could set up new electrical grids.
- “There were locations that already had many people without electricity. Then, the populations in those areas increased quickly and without enough electrical infrastructure, meaning the problem was growing larger and larger,” said Falchetta. The map also reveals little electrification progress in Central Africa, including large parts of Uganda, Burundi, Chad, and in multiple areas of the Sahel.
- Falchetta cautions that these maps only depict populations without access to an electrical grid; it likely does not account for remote communities powering lights by diesel generators or standalone solar systems, as such lights might be too dim for the satellite to detect. Small-scale solar systems are rapidly helping electrify countries like Kenya, Uganda, and Ethiopia, especially in remote areas where it may be expensive to extend the national grid. In fact, solar power systems could cover about one-fourth of new electricity demands in Africa by 2030.
- “These maps are a proxy of energy needs, a one support for policymakers as they assess current strategies and progress in electrification,” said Falchetta. “The big advantage is that the maps can be readily updated and the NASA data is free.”
Figure 23: Map of provincial changes in electrification in Africa in the period 014-2019 (image credit: NASA Earth Observatory)
• March 23, 2021: Swarms of small earthquakes in February 2021 on Iceland’s Reykjanes peninsula had experts warning that magma was moving beneath Geldingadalur valley and could soon erupt. Late on March 19, an eruption officially began as lava broke through the surface near Fagradalsfjall, one of several shield volcanoes on the peninsula. 32)
Figure 24: In an eruption not far from Reykjavik, lava poured from spatter cones along a new fissure on Reykjanes peninsula. The images were acquired with the day-night band of the Visible Infrared Imaging Radiometer Suite (VIIRS), which detects light in a range of wavelengths from green to near-infrared and uses filtering techniques to observe faint signals such as fires, electric lights, and the glow emitted by lava. During the day, the Moderate Resolution Imaging Spectroradiometer (MODIS) acquired natural-color and false-color imagery as emissions from the eruption slightly brightened clouds in the area (image credit: NASA Earth Observatory images by Joshua Stevens, using VIIRS day-night band data from the Suomi National Polar-orbiting Partnership and imagery from the Earth Observatory's Blue Marble collection. Story by Adam Voiland)
- While small in comparison to other recent eruptions in Iceland, the event was bright and large enough for NASA and NOAA satellites to observe. On March 21, 2021, the Suomi NPP satellite acquired a nighttime view of western Iceland through a thin layer of clouds (Figure 24 right). Reykjavik, Reykjanesbær, and other cities appear as bright spots in the image. The eruption appears as a new patch of light on the southwestern part of the island. For comparison, the image on the left (acquired on March 16) shows the same area a few days before the eruption.
- Lava poured from a fissure that was initially 500 to 700 meters (1,600 to 2,300 feet) long. It successively built up and then broke down mounds of cooled lava called spatter cones. Aside from crowds of onlookers and a possible archaeological site, not much has been threatened by the lava so far. Neither ash or gas emissions have been problematic either. Nonetheless, the Icelandic Meteorological Office is monitoring the volcano and is sharing the results of a forecast model.
• March 18, 2021: Gusty springtime winds turned the skies yellow and beige in mid-March 2021 across northern Mexico, New Mexico, and west Texas. A strong low-pressure system blowing along the Mexico-United States border scattered dust in an unusually long-lasting storm. 33)
- Sustained winds of 35 to 45 miles (55 to 70 kilometers) per hour —with gusts to 65 (100)—lofted abundant streams of dust from the Chihuahuan Desert. The storm lasted nearly eight hours, reduced visibility to below a half-mile in some places, and degraded air quality, particularly in the El Paso-Juárez metropolitan area.
- “The Chihuahuan Desert has been experiencing a drought in conjunction with La Niña, so conditions were even drier than usual and particularly primed for dust storms,” said Thomas Gill, a geology professor at the University of Texas–El Paso. “What was probably most unusual was the long-lasting nature of the event. Due to the relatively slow passage of the cyclone across New Mexico, El Paso experienced dusty weather basically for eight hours nonstop—more than twice as long as the historical average for dust events in the city—and until well after dark, which is also unusual.”
Figure 25: A strong low-pressure system along the Mexico-United States border scattered dust for nearly eight hours. The VIIRS instrument on the NOAA-NASA Suomi NPP satellite acquired a natural-color image of the dust storm in the early afternoon on March 16, 2021. The NOAA-16 geostationary weather satellite acquired time-lapse video of the storm, including an enhanced product focused on the dust (image credit: NASA Earth Observatory image by Joshua Stevens, using VIIRS data from NASA EOSDIS LANCE, GIBS/Worldview, and the Suomi National Polar-orbiting Partnership. Story by Michael Carlowicz)
• February 13, 2021: In early February 2021, beautiful auroras appeared to skywatchers in high latitudes and some middle latitudes of Scotland, Canada, Scandinavia, and the United States. Some photographers withstood below-freezing temperatures to capture the dancing lights in the sky. 34)
- The creation of an aurora starts when the Sun sends a surge of particles and energy—through solar flares, coronal mass ejections, or active solar wind streams—toward Earth. This surge disturbs Earth’s magnetosphere, the region of space protected by the planet’s magnetic field. The solar particles collide with the magnetosphere and compress it, changing the configuration of Earth’s magnetic field lines (such as their shape and direction). Some particles trapped along the magnetic field lines are accelerated into Earth’s upper atmosphere, where they excite nitrogen and oxygen molecules and release photons of light. The result is the dancing northern lights.
- This aurora was caused by a coronal hole that rotated into Earth’s strike zone, according to a report by space weather forecaster Tamitha Kov. A coronal hole—which appears as a dark region on the Sun’s surface—is an area of relatively cooler material in the solar atmosphere that is open to interplanetary space, sending material in a high-speed stream. This was the second occurrence of auroral activity in several days. The previous aurora occurred around February 2 from a different coronal hole that rotated towards the Earth.
Figure 26: The image shows auroras over Alaska and western Canada on February 7, 2021, as acquired by the VIIRS (Visible Infrared Imaging Radiometer Suite) on the Suomi NPP satellite. From the ground, the aurora appeared particularly bright in some regions, as the Moon was passing through its last quarter and shedding less light (image credit: NASA Earth Observatory image by Joshua Stevens, using VIIRS day-night band data from the Suomi National Polar-orbiting Partnership. Story 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. 35)
Figure 27: 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. 36) 37) 38)
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 28: Functional block diagram of ATMS (image credit: NASA)
Figure 29: Schematic illustration of ATMS (image credit: NASA)
Figure 30: Elements of the ATMS design configuration (image credit: NASA)
Figure 31: 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 32: Photo of the ATMS instrument (image credit: NASA) 39)
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. 40)
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). 41) 42) 43) 44) 45) 46) 47) 48)
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 33: 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 34: 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: 49) 50) 51)
• 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. 52)
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. 52).
Figure 35: 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. 53)
Figure 36: 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: 54)
• 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. 55)
Figure 37: Photo of the VIIRS instrument (image credit: NASA, Raytheon) 56)
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. 57)
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: 60)
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 38: 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). 61)
Figure 39: 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. 62)
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. 63)
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]. 64)
• 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. 65)
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. 66)
Figure 40: Illustration of the CrIS instrument (image credit: IPO)
Figure 41: 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 42: 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: 67)
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 43: 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. 68) 69) 70)
Table 13: Overall mission requirements for OMPS ozone observations 71)
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 44: 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: 72)
- 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 45: 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. 73)
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. 74)
Figure 46: 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. 75)
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: 76) 77) 78) 79) 80) 81)
- 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 47: Cross section of the CERES telescope (image credit: NASA/LaRC) 82)
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: 83)
• 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 48: NPP CERES data system architecture (image credit: NASA/LaRC)
Figure 49: Photo of the CERES flight modules in 1999 (image credit: NASA)
Figure 50: Illustration of the CERES instrument (image credit: NASA/LaRC)
Figure 51: Engineers inspect the CERES FM-25 sensor following the completion of thermal vacuum testing at NGC (image credit: NGC) 84)
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 53: Suomi NPP mission system architecture (NASA, NOAA)
Figure 54: SDS (Science Data System) architecture (image credit: NASA) 86)
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. 87) 88)
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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).