Introduction to Weather Satellites
The world’s first meteorological satellite, a polar-orbiting satellite, was launched from Cape Canaveral on 1 April 1960. Named TIROS for Television Infrared Observation Satellite, it demonstrated the advantage of mapping Earth’s cloud cover from satellite altitudes. TIROS showed clouds banded and clustered in unexpected ways. Sightings from the surface had not prepared meteorologists for the interpretation of the cloud patterns that the view from an orbiting satellite would show.
The spacecraft, the sensors, the communication links, the data, and the data uses of weather satellites today bear little resemblance to what they were at the time of that pioneering effort. In the decades that have elapsed, satellite weight has grown from about 100 kg to nearly a metric ton; vidicon cameras have given way to scanning radiometers; hand-drawn analyses of the data have been replaced by computer-generated products; what was analog has become digital; and capabilities have expanded to include atmospheric profiling, ocean sensing, and collecting and relaying environmental data recorded by remote reporting platforms. In addition, weather satellites now measure the space environment in which they operate. Just as their technology and uses have evolved, so have weather satellites proliferated internationally. Meteorological spacecraft in polar orbit and geostationary orbits are operated by the United States, the European Space Agency, Japan, India, Russia, and the People’s Republic of China.
Today, U.S. environmental satellites are operated by NOAA’s National Environmental Satellite, Data, and Information Service (NESDIS) in Suitland, Maryland. NOAA’s operational environmental satellite system is composed of two types of satellites: geostationary operational environmental satellites (GOES) for national, regional, short-range warning and ”now-casting,” and polar-orbiting environmental satellites (POES) for global, long-term forecasting, and environmental monitoring. The GOES and POES satellites also carry search-and-rescue instruments to relay signals from aviators and mariners in distress. Both types of satellites are necessary for a complete global weather monitoring system. In addition, NOAA operates polar-orbiting satellites in the Defense Meteorological Satellite Program (DMSP). NESDIS also manages the processing and distribution of the environmental data and images that the satellites produce each day. Figure 1 shows a current GOES spacecraft, and Fig. 2 illustrates a POES space vehicle.
NASA’s Goddard Space Flight Center (GSFC) in Greenbelt, Maryland, is responsible for the procurement, development, launch services, and verification testing of the spacecraft, instruments, and unique ground equipment. Following deployment of the spacecraft from the launch vehicle, GSFC is responsible for the mission-operation phase leading to injection of the satellite into either low-altitude polar or geostationary equatorial orbit and for the initial in-orbit satellite checkout and evaluation.
Figure 1. A geosynchronous operational environmental satellite (GOES). The function of this spacecraft is to make panoramic pictures of the world’s weather patterns from an altitude of 22,500 miles.
Figure 2. A polar-orbiting operational environmental satellite (POES). This spacecraft is a stable platform for high-resolution cameras and other sensors.
Early History of the Weather Satellite Program
Today’s advanced technology and the images of clouds shown daily on television weather forecasts may make it difficult to remember the days when there were no weather satellites. Yet the need for weather observations from space was obvious. Oceans cover about 70% of Earth, and weather observations were sparse over these areas. Observations were limited even over the continents, except over North America and Europe.
The concept and design of weather satellites were developed during the 1950s. Even earlier, in the late 1940s, pictures of Earth taken from high-altitude V-2 rockets launched at White Sands, New Mexico, showed the meteorological potential through viewing cloud systems synoptically (1). These initial images demonstrated the need for satellites.
The earliest discussion of weather observations from ”spaceships” was by Greenfield and Kellogg in a classified RAND report of 1951, later published in 1960 (2). The full potential of a satellite was recognized by Dr. Harry Wexler, chief scientist of the U.S. Weather Bureau (in the Department of Commerce, now part of NOAA). He presented his ideas at a symposium held at the Hayden Planetarium in New York City in 1954 (3). Wexler showed a simulated sketch of cloud cover over North America viewed from a satellite as if it were positioned 4000 miles over Texas. At the same symposium, Professor S. Fred Singer, then at the University of Maryland, presented his concept of a small, instrumented minimum orbiting unmanned satellite of Earth (MOUSE) to obtain a variety of atmospheric, geophysical, and astrophysical data, such as cosmic rays and ultraviolet radiation from the sun. Later, he developed these ideas in greater detail and published them in a review article in 1956 (4). Singer scanned Wexler’s high-resolution cloud picture with an array of photocells on a simulated spinning satellite and showed a meteorologically adequate reproduction of cloud patterns (5). He also discussed measuring albedo (reflection of visible solar radiation) and infrared (IR) emissions from the surface and atmosphere to determine long-term climate changes. The monograph also presented an analysis of an instrument to measure remotely the vertical distribution of ozone in the stratosphere (4).
By 1958, the United States began to launch a series of instrumented satellites through a newly established agency, the National Aeronautics and Space Administration (NASA) (6). It consolidated programs from many centers of the Department of Defense. In particular, it took over weather satellite design and testing from the U.S. Army Signal Corps. The program was headed by Dr. William Stroud and was transferred to the newly established Goddard
Space Flight Center (GSFC) of NASA. The weather satellite, labeled TIROS, incorporated some of the design concepts of the MOUSE. It had a near-polar orbit to cover almost the entire globe; it was spin-stabilized, but it used television cameras rather than the scanning photodetectors of the simpler MOUSE.
In March 1958, the Chief of the USWB, Dr. F.W. Reichelderfer, established a special unit under Wexler, Director of Meteorological Research (7). He named Dr. Sigmund Fritz as the head of the Meteorological Satellite Section. Six months later, in September 1958, Wexler sent a memo to the USWB units noting the formation of NASA and stating that the Weather Bureau would be designated as its meteorological agent to provide meteorological instrumentation, data reduction, and analysis of observations. The memo also described in detail the types of data that were expected from the satellites and the research and development work needed. Almost 2 years before the launch of the first weather satellite, he identified the following types of data that would become available within the near future:
1. cloud cover
2. heat budget of the earth
3. nocturnal cloud cover using infrared
4. “temperature” as inferred from CO2 emission in the infrared (IR)
5. ozone distribution
6. spectrum of solar radiation
The first TIROS launch demonstrated the operational value of cloud pictures, primarily for tracking hurricanes. It led directly to a Congressional authorization to set up an operational program in the U.S. Weather Bureau. NASA continued to hold the responsibility for research on satellites and instrumentation, and the Meteorological Satellite Section (MSS) of the USWB dealt with meteorological applications. As the agency responsible for operational applications, the USWB was to set the operational requirements that NASA had to satisfy in designing, launching, and operating the satellites.
The early TIROS carried two vidicon cameras—a wide-angle and a narrow-angle one. The image of the earth and clouds was formed on the vidicon tube (which is about 1 inch in diameter) and persisted for several seconds. During this period, the image was scanned and transmitted to the ground stations to receive and reconstruct the image. As soon as one image was transmitted, the next sequence was started, and thus a large segment of the globe was covered. The satellite also carried a tape recorder to store the pictures when out of range of a ground data-acquisition station. The early satellites (TIROS-1 to -8 and TIROS-10) were shaped like a hatbox and were allowed to spin along their vertical axis to keep them stable. Because of the nature of the polar orbit and the way the cameras were mounted on the spinning satellite, only limited coverage of the globe was possible.
There were two primary ground stations to command and receive the satellite data. They were located at Ft. Monmouth, New Jersey, and Kaena Point, Hawaii. At the ground stations, pictures were displayed on kinescopes for immediate viewing and photographing. In the early stages of this program, NASA had the responsibility for planning; placing the satellite into orbit; and tracking, acquiring, processing, and analyzing the data. Assistance was provided by industry and other governmental agencies. Meteorologists in the USWB/MSS were responsible for analyzing and interpreting cloud-cover data.
When TIROS-1 was launched, it was assumed that the attitude of the satellite in space relative to the fixed stars would stay the same throughout its lifetime. Analysis of the pictures showed that this was not true and extensive corrections had to be made while analyzing the pictures. The causes for this deviation were (1) the interaction between the magnetic field of the satellite and that of Earth; and (2) the decrease of gravitational force with height, which causes an object in space to tend to align itself vertically. As soon as these factors were known, they were incorporated in future satellite data processing.
To observe both day and nighttime cloud cover, radiometers were installed on the next satellite, TIROS-2, and the follow-on satellites (TIROS-3, -4, -5 and -7). All of these radiometer measurements were stored in the tape recorder on board the satellite and were transmitted to the ground station after each orbit. Using the experience gained from these early measurements, various changes were made to the follow-on instruments, which will be discussed later.
The inclusion of infrared radiometers on TIROS added extra capabilities. For example, the measurements in the 8 to 12-mm channels provided an estimate of the cloud top temperatures, and thus one could infer the cloud top heights. One of the early studies by Rao and Winston (8) showed the cloud-top temperatures and cloud heights determined over the United States using the TIROS-2 radiation data. The researchers compared the results with synoptic and aircraft data and found good agreement.
Another interesting study (9) showed the temporal and spatial variations of the outgoing long-wave radiation derived from the TIROS-2 radiometer (7 to 33-mm channel) to estimate the total outgoing long-wave radiation at the top of the atmosphere. The observed latitudinal distribution agreed well with available theoretical studies.
These early satellites also mapped ice cover over the Gulf of St. Lawrence and the Great Lakes areas. These pictures were found very useful for navigation by observing the leads in the ice cover. Another important application was monitoring the extent of snow cover during winter and the melting of snow during spring. The snow cover information was very useful for hydrological forecasting (10,11).
Tiros-Nimbus Problems (PRE-1964)
Administrative History of NESDIS. In 1960, the Meteorological Satellite Section, established in 1958 in the USWB, became the Meteorological Satellite Laboratory (MSL), and in 1962, the Meteorological Satellite Activities (MSA) with S. Fred Singer as the first Director and David S. Johnson as the Deputy Director. In the following year, it became the National Weather Satellite Center. When Singer departed in 1964, Johnson became Director. Upon the formation of the National Oceanic and Atmospheric Administration in 1972 and the accompanying reorganization, the organization was renamed the National Environmental Satellite Service (NESS). After Johnson’s retirement in 1982, it became the National Environmental Data and Information Service (NESDIS). Dr. John McElroy was the Assistant Administrator until 1986. Dr. William Bishop served as Acting Assistant Administrator until Tom Pyke became the Assistant Administrator of NESDIS. He continued until 1992. After Pyke, Robert Winokur held the position until 1999, when Greg Withee became the Assistant Administrator of NESDIS.
In June 1962, the Chief of the USWB appointed Dr. S. Fred Singer as Director of the Meteorological Satellite Activities. In a memo to his staff (Annex 5 of Ref. 7), he described the policies and the organization of the unit and noted in detail the “operational” responsibility for weather satellites bestowed on the USWB by the U.S. Congress in PL 87-332. Eighteen months after the launch of the first satellite TIROS-1, a fully operational entity was in existence.
As part of its responsibility, NASA developed the concept of the Nimbus research satellite. It was much larger, more complicated, and certainly more expensive than the simple TIROS. It was stabilized in three axes and was designed as a platform for a variety of instruments to view Earth by remote sensing. In addition to carrying out an atmospheric research program, Nimbus was also designed to provide a test bed for advanced instruments and systems, later to be transferred to the operational program (7).
Nimbus was primarily designed by Dr. Rudolph Stampfl and his associates at NASA’s Goddard Space Flight Center (GSFC) in 1959. The objectives of the design were (1) a near-polar orbit to permit observation of the entire Earth (from pole to pole), (2) Earth-stabilization so that the cameras and other sensors could always point toward Earth, (3) a retrograde (east to west) orbit inclined about 80° to the equator so that the satellite crosses the equator at local noon (northbound) and local midnight (southbound) in every orbit, (4) an altitude of 1000 km (600 nautical miles) to avoid Earth’s radiation belt and to provide enough overlapping coverage at the equator, and (5) modular construction to allow easy exchange of sensors and communication modules. Originally, the plan was for GSFC to integrate and test the spacecraft. However, in 1961, several separate contracts were awarded for the various subsystems, and General Electric’s Missile and Space Vehicle Department handled the final integration. Nimbus was a totally new system and was more complicated than the TIROS. The program was in trouble right from the beginning, and deadlines could not be met in completing the systems for integration and testing.
The second TIROS satellite was launched on 23 November 1960. Its ability to locate and track weather fronts, hurricanes and other tropical storms proved to be a boon for meteorology. In addition to the USWB and its clients, the Department of Defense stated its interest in operational satellite data in no uncertain terms in Congressional hearings (12).
The evolution of the weather satellite program in the Department of Commerce is well described by P.K. Rao (7). He relates an interesting episode that took place in the early 1960s when the TIROS satellites were being considered for operational use. Some senior people in NASA wanted to consider it a research program and opposed immediate operational use of TIROS data. NASA refused the USWB use of the TIROS data for operational weather analysis for several weeks after the launch of TIROS. The two main groups that wanted the satellite data to be operational were the USWB and DOD Weather Services.
In October 1960, to settle some of the differences (research vs. operations) with regard to TIROS satellite operations, an interagency group consisting of NASA, USWB, DOD, and FAA established the Panel on Operational Meteorological Satellites (POMS) under the auspices of the National Coordinating Committee for Aviation Meteorology (NACCAM). The Chief of the USWB chaired NACCAM. The first chairman of POMS was Edgar Cortright of NASA; Dr. Morris Tepper of NASA served as secretary. This group developed the report ”Plan for a National Operational Meteorological Satellite System (NOMSS),” completed in April 1961, and submitted to Congress (12).
POMS gave operational responsibility for weather satellites to the USWB, which then became the position of the Kennedy administration. Under this plan, Nimbus was to be the ultimate operational weather satellite but would also serve as a platform for developing instruments and technology. NOMSS was approved by President Kennedy as his fourth national goal; the first was to put a man on the Moon. On 25 May 1961, in President Kennedy’s address to the Congress on ”Urgent National Needs” (13), he requested funding for these activities (approximately $53 million dollars) to be given to the USWB.
NOMMS said that the operational meteorological satellite system should
• satisfy the meteorological requirements of all users;
• phase into operation at the earliest date;
* capitalize on the continuing research and development program; and
* serve the United States first, but where possible, also serve international needs.
Already then, Stroud and his NASA colleagues foresaw problems as Nimbus was pushed into an operational role while still basically a research satellite. Because of the delay in Nimbus, new instruments could not be tested in time to incorporate them into operational weather satellites (7). NASA felt that Nimbus should be fully tested before declaring any instruments ready for operation.
Funds were appropriated for the USWB, which gave it fiscal control of the operational program, but NASA wanted to give responsibility to the USWB only when the system became operational. Nimbus, however, was a long way from becoming operational. As a result of the supplemental appropriation for the USWB of $48 million for fiscal year 1962, the Nimbus Operational System (NOS) agreement was signed; USWB gave up of most of its responsibility to NASA although it had the funds appropriated for it.
As Richard Chapman recounts in his history of the administrative, political, and technological problems of developing a U.S. weather satellite, the USWB was then in a weak position (12). It had no permanent director for its satellite activities and insufficient competence in the technical areas (outside of meteorology) to match those of the large NASA group at the GSFC. Change came in the spring of 1962, when the Commerce Department selected J. Herbert Hollomon for the position of assistant secretary for research and technology and in June 1962, when atmospheric and space physicist S. Fred Singer, then a professor at the University of Maryland, was appointed director of the weather bureau’s satellite efforts (12).
On taking the position of director, Singer renamed the organization the National Weather Satellite Center (NWSC) and convened a group to correlate the requirements of operational users, including those of the DOD. The group was particularly concerned about the delays in the Nimbus program, that its capabilities had been scaled down, and that its lifetime and period of performance were short. Eventually, the delay lasted 2 years because of a variety of problems that GSFC as the integration contractor could not handle efficiently. At that time, Singer, as Director of the NWSC, decided to provide funds to build a few more TIROS satellites to maintain continuity of operations, rather than continue to fund NASA to develop Nimbus (12).
Gradually, a shift took place away from the NASA-USWB interagency agreement and NOMSS. Hollomon and Singer became particularly concerned about the accountability of USWB funds committed to NASA. What could the Department of Commerce and WB show the Congressional oversight committee in the way of accomplishments with its appropriated ”no-year” funds? First, Singer decided that additional interim TIROS satellites were needed to fill the gap while waiting for Nimbus to become operational (12). Then, analyses by NWSC demonstrated that an advanced TIROS could handle some of the Nimbus functions, including APT, the all-important direct readout feature of cloud data that the DOD wanted. The main problem with Nimbus, aside from the delay, was its complexity and therefore the question of reliability for operational purposes. NASA itself only foresaw a lifetime of less than 6 months, whereas NWSC, concerned about cost, was looking for satellites that would operate for 3 to 5 years.
In the meantime, while the Nimbus cost had doubled, the USWB had reached the conclusion that an interim improved TIROS would be adequate and that something better than Nimbus was required for the long term. The NWSC studies showed that the cost of the operational program could be cut in half.
During the summer of 1963, a technical battle ensued between GSFC/ NASA and the NWSC/ Department of Commerce, that covered many technical areas relevant to the operational weather satellite system, including optimum orbit, readout stations, instruments, and radiation protection.
The main NASA Command and Data Acquisition (CDA) station was near Fairbanks, Alaska. The turning point came when NWSC initiated its own technical studies and demonstrated that, in the proper orbit, the simpler satellite would require only one readout station (in Alaska) and that a Canadian station was not required. Ultimately, Singer did not accept the NASA analyses and
Secretary Hollomon formally withdrew support for the Canadian readout station, which was to be financed with money appropriated for the USWB. He argued that Nimbus had become too costly compared to an improved TIROS satellite. If NASA would not supply the spacecraft, then the DOD was willing to step in and manage the program (12).
This proved to be the final deciding factor. The TIROS operational satellite (TOS) was developed under NASA direction. It had many of the features of the Nimbus satellite and some of its instruments. However, it was simpler and cheaper. Instead of an active system of attitude control, it was a spin-stabilized wheel in a sun-synchronous, near-polar orbit. Most important, the budget of the operational program had been cut by nearly half, and Nimbus had lost its operational mission.
Nimbus 1 was finally launched from the Pacific Missile Range on 28 August 1964 on a Thor-Agena rocket but failed after 26 days. However, later and improved Nimbus satellites provided a test bed for instruments and technology that eventually found their way into the operational mission. The first Nimbus carried the advanced vidicon camera subsystem (AVCS) to provide global coverage. It also carried the automatic picture transmission (APT) subsystem to provide pictures of local cloud patterns directly to suitably equipped weather stations as the satellite passed over them. The AVCS and APT cameras provided images only during the daylight portion of the orbit. Nimbus also carried an improved version of a radiometer called the high-resolution infrared radiometer (HRIR) to observe in the 8- to 12-mm window region, and in the region of 3.4 to 4.2 mm (a clear window). The Nimbus also carried a radiometer, similar to the TIROS radiometer. This was called the medium-resolution infrared radiometer (MRIR) and again the window channel was changed to 10-11 mm so that the absorption due to ozone and water vapor could be eliminated (a much cleaner window region of the IR spectrum).
Between 1964 and 1979, NASA launched seven Nimbus satellites and tested prototype operational sensors for use in future NOAA polar-orbiting satellites (14).
Satellite Development—Early 1960 to Present
The early satellites TIROS-1 to -8 and TIROS-10 were shaped like a hatbox and were allowed to spin along their vertical axis to keep them stable. Because of the nature of the polar orbit (50° N-50° S) and the way the cameras were mounted on the spinning satellite, only limited coverage of the globe was possible. To obtain day and night coverage of the entire globe, radiometers were installed to observe in both the visible and infrared spectral regions. The rapid improvements in the spatial and spectral resolution of the radiometers made it possible to eliminate the onboard cameras. Both day- and nighttime images could be constructed from the radiometer measurements.
The first change in the weather satellite design occurred in 1965 in TIROS-9. The hat shape was changed to a cartwheel and the cameras were mounted along the radius 180° apart. The cameras could look straight down every time the satellite turned on its axis (at approximately 12 rpm). The spacecraft could view the entire Earth in a 24-hour period as it rolled along its orbit. The launch of the TIROS-9 series increased the daily coverage capability of the satellite substantially. This was also the beginning of the TIROS operational system (TOS) satellites.
The First Tiros Operational System (TOS) Satellites. The first operational weather satellite system of the world started when the Environmental Sciences Services Administration (now NOAA) satellites, were launched ESSA-1, on 3 February 1966 and ESSA-2 on February 28, 1966. (The satellites reflect the name of the agency. The system consists of a pair of ESSA satellites in a sun-synchronous orbit; each is configured for a specific mission.) The advanced vid-icon camera system (AVCS) obtained global imagery, which transmitted to the Command and Data Acquisition (CDA) stations at Wallops Island, Virginia, and at Fairbanks, Alaska. The CDA stations relayed the data to the National Environmental Satellite Service (NESS) in Suitland, Maryland, for processing and distribution to forecasting centers in the United States and other nations. The odd-numbered satellites (ESSA-1, -3, -5, -7, and -9) that had redundant AVCS systems were the global readout satellites. Even-numbered satellites (ESSA-2, -4, -6, and -8) were equipped with redundant automatic picture transmission (APT) cameras, and pictures from these cameras were directly transmitted to ground stations located around the world.
Improved Tiros Operational Satellite (ITOS) System (1970-1978). The new generation ITOS-1 satellite was launched on 23 January, 1970. The system carried both the AVCS and APT systems and a two-channel scanning radiometer (SR) that provided day and night coverage. The data from the SR were available by immediate transmission for local use and in a stored mode for later playback at the CDA station. The IR scanning radiometer made global observation of the atmosphere and surface areas available once every 12 hours from a single ITOS spacecraft. The second ITOS was launched on 11 December 1970, and it was named NOAA-1 (after the National Oceanic and Atmospheric Administration). The ITOS system evolved further from the development of ITOS-D satellites. These had a new redundant sensor complement to provide day and night imaging by the very-high-resolution radiometer (VHRR) and the medium-resolution scanning radiometer (SR). The VHRR and SR systems replaced the AVCS and APT cameras. The new ITOS system also carried the vertical temperature profile radiometer (VTPR) for obtaining the vertical temperature and moisture distribution in the atmosphere and a solar-proton monitor (SPM) for measuring solar protons and electron fluxes in the vicinity of the satellite. This second generation of satellite continued until 1978.
Third Generation of Operational Satellites: TIROS-N/NOAA-A to -D.
These spacecraft covered a period from 1978 to 1981 and had a new and improved complement of systems. The advanced very-high-resolution radiometer (AVHRR) provided data for day and night imaging in the visible and infrared. It also provided observations to extract the sea surface temperature (SST), snow and ice distribution, and the Earth-atmosphere radiation budget. The TIROS operational vertical sounder (TOVS) provided vertical distribution of temperature and moisture in the atmosphere. The satellite also had a data collection system (DCS) to collect environmental data from stationary and moving platforms such as buoys, and remote hydrological stations. This satellite could broadcast data directly to local users and had a tape recorder to store data and transmit it to the CDA stations at Wallops Island and Fairbanks. The TIROS-N series of satellites operated in polar orbit at an altitude of approximately 850 km.
The Advanced TIROS-N (ATN)/NOAA-E to -J System (1983-1994).
These spacecraft were modified to add some new and improved sensors: a search-and-rescue (SAR) system, Earth radiation budget experiment (ERBE), and a solar backscatter ultraviolet (SBUV) radiometer to measure stratospheric ozone distribution. The system also consists of two polar-orbiting satellites; operating as a pair, they provide environmental data for the entire globe, four times a day.
NOAA-K Series (1996 to Present). This is the latest in the Advanced TIROS-N series that started with NOAA-14. This satellite system carried a new version of the AVHRR-3 and is a six-channel instrument. It has an improved HIRS-3 instrument and an advanced microwave sounding unit-A (AMSU-A) to measure temperature and moisture from the surface to the upper stratosphere. The satellite also carried the British-built AMSU-B to measure the vertical distribution of water vapor in the atmosphere, a space-environment monitor (SEM) to measure the charged particles entering Earth’s atmosphere, SAR instruments, and data collection instruments.
Geostationary Environmental Satellites—History. The NOAA GOES program was a direct outgrowth of NASA’s Applications Technology Satellite (ATS) program. It was initiated in 1966 to demonstrate communications technology by using a satellite in a geostationary orbit. The major objective of the early ATS satellites was to test whether gravity would anchor the satellite in a 24-hour synchronous orbit (22,300 miles above Earth’s surface) over the equator, allowing it to orbit at the same rate as Earth turns, thus seeming to remain stationary. The excess capacity of the spacecraft allowed including meteorological sensors for experimental observations of Earth from a geosynchronous altitude. A spin-scan camera developed by Professor V. Suomi of the University of Wisconsin provided continuous images of the sunlit Earth disk every half hour. The nearly continuous imagery proved the ability of the spacecraft to monitor the evolution of weather systems in real time, particularly severe weather. Another satellite in this series, ATS-3, was launched in 1967 to cover the Western Hemisphere. The next in this series, ATS-6, was totally different; it was a three-axis-stabilized spacecraft intended primarily for communication experiments from geostationary orbit. It carried a meteorological sensor, the geostationary very-high-resolution radiometer (GVHRR), a two-channel radiometer scanning in the visible range (0.55-0.75 micron) and the IR (10.5-12.5 micron). Because of the IR, it was possible to image during the day and night.
Synchronous Meteorological Satellites. NASA launched two synchronous meteorological satellites (SMS), SM-1 in May 1974 and SMS-2 in February 1975, to demonstrate their use for weather forecasting. After the successful launch of these satellites, NASA turned the program over to NOAA for operation, and they were renamed geostationary operational environmental satellites (GOES). Geostationary Operational Environmental Satellites (GOES). GOES satellites are a mainstay of weather forecasting in the United States. They are the backbone of short-term forecasting or ”now casting.” The real-time weather data gathered by GOES satellites, combined with data from Doppler radars and automated surface observing systems, greatly aid weather forecasters in providing warnings of thunderstorms, winter storms, flash floods, hurricanes, and other severe weather. These warnings help to save lives and preserve property.
The United States operates two meteorological satellites in geostationary orbit, one over the East Coast and one over the West Coast, that give overlapping coverage of the United States. Currently, GOES-8 and GOES-10 are in operation. The GOES satellites are a critical component of the ongoing National Weather Service modernization program, aiding forecasters in providing more precise and timely forecasts. The next GOES-11 satellite (GOES-L) launched in 2000 is stored in orbit, and GOES-12 launched in 2001 is also stored in orbit. They will be activated when one of the current GOES satellites fails. They are the first of the NOAA satellites equipped with a solar X-ray imager (SXI), an instrument that can detect solar storms.
Defense Meteorological Satellite Program (DMSP). Since the mid-1960s, the U.S. Air Force has operated polar-orbiting meteorological satellites. The observations have emphasized high-resolution and low-light imaging rather than atmosphere profiling. The DMSP system maintained two satellites at any given time that crossed the equator in midmorning and late evening. Some of the later satellites carried microwave imaging and sounding units; some improved versions of these instruments were incorporated in the NOAA polar operational satellites. So far, about 20 DMSP satellites have been flown, primarily for use by the Defense Department.
International Program Cooperation. In the 1980s, NOAA had to balance the high cost of space systems and the growing need to provide a complete and accurate description of the atmosphere at regular intervals as inputs to numerical weather prediction and climate monitoring support systems. This led NOAA to enter into discussions and agreements at the international level with the European Organisation for the Exploitation of Meteorological Satellites (EU-METSAT). The goal of this cooperation is to provide continuity of measurements from polar orbits, cost sharing, and improved forecast and monitoring capabilities by introducing new technologies.
Several countries recognized the advantages of monitoring Earth and its environment from space and have launched both polar-orbiting and geosynchronous satellites. The operators include the European Space Agency (a consortium of several European countries), Japan, Russia, India, and China. Under an agreement reached by the satellite operators under the auspices of the World Meteorological Organization (a U.N. agency in Geneva, Switzerland), the locations of geosynchronous satellites were distributed to provide global coverage. Thus, the two U.S. satellites, a European satellite, a Japanese satellite, and a satellite from India provide complete coverage continuously from about 60° Nto 60° S. Satellite data sets and products were coordinated to ensure maximum compatibility among the operators of the geosynchronous satellites.
Russia (the former Soviet Union) has launched a series of polar-orbiting satellites in the Meteor series to obtain cloud cover, snow and ice extent, and the Earth radiation budget, and also a few sounding instruments to measure the vertical distribution of temperature and moisture for weather prediction models.
The European Space Agency is planning to launch a new generation of polar-orbiting weather satellites that will be discussed under the future satellite program.
Satellites by their nature have to rely on remote sensing. The fundamentals are elaborated in a number of topics (15-21). We will discuss the subject in four topics:
1. reflection and scattering of solar radiation
2. thermal emission from the surface and from the atmosphere
3. active probing using radar and lidar
4. other applications
Reflection and Scattering of Incident Solar Radiation. This can take place at wavelengths ranging from the near-infrared (IR) around 3 microns down to the near-ultraviolet of about 0.28 microns. Beyond 2 microns, there are important IR absorption bands, principally from water vapor, carbon dioxide, and from other minor atmospheric constituents (Fig. 3).
The most important reflection comes from clouds in the atmosphere and snow and ice on the surface. The reflection coefficient, the so-called albedo, approaches 100% in many cases. On the other hand, the albedo of the ocean is less than 10% except for areas of ”sun glint” where the reflection is specular. The patterns of reflection and their changes with time lend themselves to meteorological analysis, as discussed in the next section.
In addition to meteorological applications for weather prediction, observations of so-called aerosols, including dust, smoke, and even locust swarms, yield important information for a variety of purposes. In addition, spectral data at different wavelengths (color) can give information about agricultural crops, the health of forest systems, ocean productivity, and even about the mineral content of the soil (10,11). As discussed in specialized texts, measurement of the polarization of reflected and scattered light yields additional information about the optical and physical properties of the scattering medium.
Figure 3. Spectral curves of solar radiation incident at the top of the atmosphere and at the surface of Earth for the Sun at zenith on a clear, cloud-free day.
Backscattered radiation in the near UV region between 0.28 and 0.32 microns can be used to measure the amount and vertical distribution of stratospheric ozone. This technique was analyzed before satellites were launched (4) and was first tested on Nimbus. It has now become operational and is used to monitor ozone worldwide, including tracking the Antarctic ozone hole. Sulfur dioxide gas emitted by volcanoes into the stratosphere also absorbs strongly in the near ultraviolet; but by choosing the right wavelengths and adequate spectral resolution, one can distinguish between ozone and sulfur dioxide. Emission from the Atmosphere and Surface. Corresponding to the lower temperature of the surface and atmosphere, compared to the Sun, the emission wavelength range covers from about 4 microns into the far infrared beyond 20 microns and also the microwave region. The important feature here is the so-called “window” of the atmosphere. In the absence of clouds, IR emission from the surface in the region between 8 to 12 microns can penetrate the atmosphere and escape into space where it is observed by a satellite. (Fig. 4). Outside the window region, the atmosphere is opaque in the infrared because of strong absorption bands, principally from water vapor and carbon dioxide. (There is also absorption by stratospheric ozone at 9.6 microns in the window region.) Water droplets absorb and emit strongly in the infrared so that IR detectors from the satellite view only the tops of clouds. Because temperature decreases sharply in the troposphere, the IR emitted from cloud tops can be used to obtain an estimate of the pressure and altitude of the cloud tops.
The great advantage of infrared emissions is that they can be measured at night and are easier at that time. During the day, there is some interference from solar radiation in the infrared. In the absence of clouds, under clear sky conditions, one can measure the surface temperatures of the ground and soil and get some determination of soil moisture from the diurnal variation. Information from the surface of the ocean provides a measure of temperature; however, it relates to the skin of the sea surface and is heavily influenced by the sea state, foam, wave action, and therefore surface winds. In addition, one has to be careful in comparing IR measurements of SST with measurements from ships because they refer to different layers of the upper ocean.
When the atmosphere is clear, and there are no clouds, infrared emissions from the 15-micron band of carbon dioxide can be used to derive the vertical distribution of temperature in the atmosphere. This method was first suggested by Lewis Kaplan and was worked out in greater detail by David Wark and others at the NWSC and by Rudolph Hanel and Wm Bandeen at NASA. Mathematically, the problem is that of determining the kernel of an integral, when the integrals are observed at several wavelengths around 15 microns. This deconvolution problem also enters into the determination of atmospheric temperature distribution from microwave measurements. (The latter have an advantage over IR measurements because they can be carried out in the presence of clouds.) A similar problem occurs in measuring the vertical distribution of ozone (4); it is somewhat simpler because in the UV, only scattering and absorption are important but not emission.
Infrared radiation from the surface can provide interesting information on ground cover vegetation and can measure desertification. The Hyperion instrument on the NASA Earth Observing-I satellite, launched in November 2000, collects reflected radiance in 220 spectral bands covering the range from 0.4-2.5 microns. Preliminary research results are reported in Ref. 22; it is not clear yet whether this will lead to operational use of the technique.
Measuring the emission of microwaves from the surface and from the atmosphere has proven to be immensely useful. An early experiment in 1964 measured emission from the sea surface and demonstrated that the energy emitted, hence the emissivity, depended primarily on the sea state (23). Microwaves can measure such quantities as snow cover, precipitation, and thunderstorms (24,25). Thermal microwave emission from water vapor can be used to measure atmospheric humidity, an important quantity for studying global climate change. Microwave emission from molecular oxygen can be used to measure the bulk temperature of the troposphere and the lower stratosphere, as demonstrated in careful analyses by Christy and Spencer (26). As discussed later, satellite microwave data indicate that the atmosphere has not warmed perceptibly since global temperature observations began in 1979. Active Probing with Lasers and Radar. Radar reflection from the sea surface can determine the sea state and thereby surface winds. This has become an operational application because wind field patterns play an important role in weather prediction. Radar reflection from the land surface can produce accurate determinations of topography, including even snow depth. Finally, radar can be used to measure precipitation, especially useful over the oceans where other observations are not available. Satellite-borne synthetic aperture radar (SAR) has been used in many applications (see the Applications Section below). A recently reported use is detecting of urban sewage and storm water runoff from urban areas that cause marine pollution (27).
Radar scatterometers have provided nearly continuous coverage of Earth since 1991 on satellites of NASA, European Space Agency (ESA), and Japan. Frequencies have ranged from 5.3 to 14.6 GHz, and both vertical and horizontal polarization were measured. Applications include Greenland and Antarctic ice sheets, sea ice, soil moisture, and vegetative coverage (28,29).
Laser measurements are still in their infancy. Ideally, one would like to measure the Doppler shift of reflections from particles in the atmosphere and thereby deduce horizontal wind velocities.
Another application, still on the drawing board, uses the absorption in the D-band of oxygen molecules around 0.76 microns to measure surface pressure in the absence of clouds (30). When clouds are present, the technique measures the pressure and altitude of cloud tops. Combined with the temperature of the cloud tops, this amounts to vertical probing of the atmosphere. Systems analysis shows that internal noise is negligible and that background is not serious, even in daylight. Compared with the corresponding passive method using the Sun as a source, the laser method can be used at night, can discriminate cloud versus surface reflections, and may be able to determine altitude, pressure, and (by IR flux measurement) the temperature at selected points in the atmosphere. If successful, the method will have important applications to cloud studies and to oceanography.
Other Applications Of Remote Sensing. More refined measurements, based on wavelength dependence, polarization measurements, and time variability, can be used to deduce such important quantities as soil moisture, ocean productivity, and the properties and nature of aerosols, such as size distribution and their optical parameters (17,18,21). Besides weather satellites, other kinds of satellites can also supply data important for meteorology. For example, the Global Positioning System can be used to measure upper tropospheric water vapor by studying the time delays at the two different radio frequencies used by GPS. The TOPEX satellite can be used to measure the height of the sea surface, from which one can derive the location and strength of ocean currents. Finally, astrophysical satellites can measure solar radiation, its variability in the visible and ultraviolet, and the nature and flux of solar particulate radiation impacting on Earth’s atmosphere.
The earliest meteorological results from TIROS were published in three articles soon after launch (31-33). By the end of April 1960 (almost 30 days after launch), a number of case studies of meteorological phenomena observed by TIROS were begun by a team of meteorologists in the Meteorological Satellite Section of the USWB. These studies included several large-scale cyclonic vortices over the United States, the North Atlantic, and the North Pacific; cloudiness in the tropical regions of the South Pacific; cellular arrangements of cumulus clouds over the Atlantic and Pacific Oceans in temperate latitudes; cloud streets in the Caribbean, cloudiness associated with severe thunderstorms and tornadoes; ice in the Gulf of St. Lawrence; orographic clouds in various parts of the world; snow cover in mountain regions; and sun glitter on the ocean surface. Several technical reports were published by USWB and NASA in the following months (7).
The TIROS pictures received at the ground stations were recorded on 35-mm film by a kinescope camera, either during a satellite readout or by playing back the data recorded on magnetic tape. The film was processed immediately to make transparencies for projection and for prints. Geographic reference grids were overlaid on these pictures to determine the location where the pictures were taken. These overlay grids were generated by taking into account the position of the satellite, the time when the picture was taken, the direction in which the camera was pointing, and other parameters connected with the satellite spin axis. Once the grids were overlaid on the pictures, cloud analyses (called neph-analyses) could be performed, showing cloud types and extent of coverage. These maps were sent by facsimile to weather stations around the globe for immediate use. Within 48 hours of the TIROS-1 launch, such pictures and nephanalyses were made available to USWB meteorologists, the U.S. Air Weather Service, and the U.S. Naval Weather Service. The information was limited to areas where sunlight was available.
The introduction of infrared sensors in radiometers on TIROS-2 and the follow-on satellites, starting from November 1960, enabled continuous day and nighttime coverage. Three types of instruments were used: (1) a five-channel scanning radiometer, (2) a two-channel medium-resolution radiometer, and (3)a two-channel omnidirectional radiometer. Of the three instruments, the five-channel one was the most important. It consisted of the following:
1. 5.9-6.7 mm to measure atmospheric water vapor (based on strong absorption in this spectral region);
2. 8 to 12-mm atmospheric window to measure surface temperatures under cloud-free conditions and cloud temperatures and heights and to obtain nighttime images;
3. 0.2-5 mm to measure the albedo of the earth, clouds, etc. (reflectance);
4. 7.0-30 mm to measure the total outgoing long-wave radiation at the top of the atmosphere;
5. 0.5-0.7 mm in the visible part of the spectrum to measure the reflected radiation and create images during the daytime.
The sensors were mounted in the satellite at an angle of 45° to the spin axis of the satellite. The scan was produced by the spin of the satellite. The movement of the satellite provided coverage along the track. Because of the spin of the satellite, the sensors looked alternatively at space and at Earth. The field of view of the radiometer was approximately 30 miles.
All of these radiometer measurements were stored in the tape recorder on board the satellite and transmitted to the ground station after each orbit. The data were processed after reception at the ground station. Based on the experience gained from these early measurements, various changes were made in the follow-on instruments, which will be discussed later.
The inclusion of infrared radiometers on TIROS added extra capabilities. For example, the measurements in the 8- to 12-mm channels provided an estimate of cloud top temperatures, and thus one could infer the cloud top heights. One of the early studies by Rao and Winston (8) showed the cloud top temperatures and cloud heights determined over the United States using the TIROS-2 radiation data. The researchers compared the results with synoptic and aircraft data and found good agreement. It was also pointed out in this paper that the 8- to 12-mm window region is not clean and there is a considerable amount of absorption due to water vapor and ozone; thus appropriate corrections needed to be applied.
Satellite pictures were also used to observe and map the ice cover over the Gulf of St. Lawrence and the Great Lakes. These pictures were useful for navigation by showing the leads in the ice cover. Another important application was to monitor the extent of snow cover during winter and the melting of snow during spring. The snow cover information was useful for hydrological forecasting.
In the early days of the satellite program, it was realized that in addition to the cloud information, the temperature and moisture distribution with height in the atmosphere is essential for forecasting. Numerical modeling of the atmosphere was gaining momentum at this time, and observations over the vast oceanic regions and other data-void regions of the world were needed to fill the gaps in these models. A prototype instrument called the satellite infrared spectrometer (SIRS) was under development within the Meteorological Satellite Laboratory. The first sounder was on the Nimbus satellite launched in 1969. Observations from the SIRS instrument were used to derive the vertical distribution of temperature (and, to a limited extent, moisture) over the oceanic regions. The satellite-derived soundings were useful for numerical weather forecast models, particularly over the oceanic regions, where radiosonde data are not available. NASA was also developing another sounder at the same time, called the vertical temperature profiling radiometer (VTPR). Because of the high spectral resolution of the VTPR, it was superior to the SIRS. Immediate plans were made to improve the VTPR instrument to operational status and move it to the NOAA polar satellites. The first operational sounder was launched on NOAA-2 in 1972. The sounders continued on all polar-orbiting satellites from that period.
In addition to the visible and infrared portions of the spectrum, satellites also started to exploit the ultraviolet, using the backscatter technique to measure the amounts and vertical distribution of ozone. Such instruments as TOMS and SBUV were first flown on Nimbus. They were then transferred to the operational weather satellites.
Figure 5. Vegetation Index: Vegetation condition products are generated from the AVHRR. The red color delineates the areas that have severe vegetative stress; the colors from yellow to blue indicate fair to favorable conditions. These images compare the global vegetative health conditions for 1999 (top) and 1998 (bottom).
Satellites have also exploited another region of the electromagnetic spectrum, measuring the passive (thermal) emission of microwaves from the surface and from atmospheric components. An early experiment, conducted from a blimp over Biscayne Bay, Florida, demonstrated the high emissivity from foam produced by waves (and thus the sea state). Nowadays, active microwave (radar) determines the sea state by scattering.
A comprehensive account of weather satellite applications is given in various references. Here we will provide two examples to demonstrate the wide range of results obtainable by remote sensing from satellites. Both of these images were made using the advanced very high resolution radiometer on POES spacecraft. Figure 5 is a composite picture of Earth showing the state of worldwide vegetation. Figure 6 is a picture of Hurricane Floyd. This is an example of the high-resolution pictures of various weather patterns that can be made by using satellite-borne instruments.
Figure 6. Hurricanes: This image of Hurricane Floyd on 14 September 1999 as it hits Eleuthra Island in the Bahamas was generated using a composite of channels 1, 2, and 4 from the AVHRR instrument in its high-resolution imaging mode of 1.1 km.
Weather satellite instruments were not designed to determine long-term trends of atmospheric parameters. Changes over decadal timescales generally require using instruments from different satellites and careful calibration. Yet, with great care it has been possible to use much of the data for such purposes.
Four kinds of measurements are possible; the first two refer to the atmospheric energy balance:
1. Albedo measurements over long time spans can, in principle, determine any changes in the energy input to Earth. Calibration is quite difficult here, but attempts have been made to establish long-term trends in cloudiness and surface albedo through changes in human land use (34).
2. The converse measurement measures the outgoing long-wave radiation (OLR) from Earth, including the IR emitted from the surface through the atmospheric window and the IR emitted from the atmosphere, mainly from upper tropospheric water vapor, carbon dioxide, and clouds (35,36).
3. Rather than concentrate on the energy balance, a complementary technique monitors long-term changes in global atmospheric temperature. For this purpose, the microwave sounding unit (MSU) carried by weather satellites has turned out to be the principal instrument (26). There is no perceptible trend in global mean temperature since observations started in 1979. Surface observations from weather stations do show a warming during the same period (37); this discrepancy has not yet been resolved (38). However, independent data from radiosondes in weather balloons confirm the satellite data that there has been no atmospheric warming. Proxy data of surface temperature from tree rings and ice cores also show no surface warming trend since about 1940. Thus the preponderance of data indicates little if any warming in the last 60 years.
4. Finally, thanks to satellites, it may possible to measure long-term changes in global precipitation, particularly over the oceans where there are no good data. We do have long-term measurements of severe storms and tropical cyclones; land observations and also satellites have so far shown no clearly established trends (37). As reported, the intensity and frequency of North Atlantic hurricanes has decreased. There has been no report of discernible trends for severe storms, El Ninos, and similar meteorological phenomena.
Continuity and Future of Operational Satellite Programs
Figure 7 shows the planned launch of polar-orbiting and geostationary operational satellites. It should be emphasized that the actual schedules will depend primarily on the need for replacement satellites, the availability of spacecraft,and a launch vehicle. It is also assumed that the new generation of satellites will have a 5-year life expectancy and that all launches are successful. It should be pointed out that the satellites designated by letter are designated by a number after a successful launch (e.g., GOES-N to GOES-13; NOAA-M to NOAA 17).
Figure 7. Continuity of Operational Satellite Programs. NOAA satellite launches scheduled to maintain continuity.
The U.S. government has traditionally maintained two operational weather satellite systems; each has a 30-plus year history of successful service: NOAA’s polar-orbiting operational environmental satellite (POES) and DOD’s Defense Meteorological Satellite Program (DMSP). Recent changes in world political events and declining agency budgets prompted a reexamination of combining the two systems.
In May 1994, President Clinton signed a presidential directive to merge the civilian POES system and the DMSP into a single system to reduce costs, while continuing to satisfy the U.S. operational requirements. On 3 October 1994, NOAA, DOD, and NASA created an Integrated Program Office (IPO) to develop, manage, acquire, and operate the NPOESS system. The Integrated Program Office concept provides each of the participating agencies with lead responsibility for one of three primary functional areas. NOAA has overall responsibility for the merged system and is also responsible for satellite operations. NOAA is also the primary interface with the international response and civil user communities.
DOD is responsible for supporting the IPO for major systems acquisitions, including launch support. NASA has primary responsibility for facilitating the development and incorporation of new cost-effective technologies into the merged system. Although each agency provides certain key personnel in their lead roles, each functional division is staffed by triagency work teams to maintain the integrated approach.
As an early step in the merging process and the first tangible result of the NPOESS effort, Satellite Control Authority for the existing DMSP satellites was transferred in May 1998 from the U.S. Air Force Space Command to the NPOESS Integrated Program Office. The command, control, and communications functions for the DMSP satellites have been combined with the control for NOAA’s POES satellites at NOAA’s Satellite Operations Control Center (SOCC) in Suit-land, Maryland. The DMSP satellites are being ”flown” by civilian personnel at the SOCC. This is the first time in the 30-plus-year history of this DOD program that DMSP satellites have not been flown by Air Force personnel. A backup satellite operations center manned by USAF crews is also contemplated.
On 13 December 1999, a new Department of Defense meteorological satellite was launched by the U.S. Air Force and is being operated by NOAA. The satellite is the next in a series of the Defense Meteorological Satellite Program. This is the first DMSP whose postlaunch checkout was conducted from NOAA’s Satellite Operations Control Center in Suitland, Maryland.
The NPOESS Preparatory Project (NPP) is a proposed joint mission to extend key measurements in support of long-term monitoring of climate trends and of global biological productivity. It extends the measurement series being initiated with EOS Terra (MODIS) and EOS PM (AIRS, AMSU, HSB) by providing a bridge between NASA’s EOS missions and the NPOESS system. The NPP mission will provide operational agencies with early access to the next generation of operational sensors, thereby greatly reducing the risks incurred during the transition. This will permit testing of advanced ground operations facilities and validation of sensors and algorithms while the current operational systems are still in place. This new system will provide nearly an order of magnitude more data than the current operational system. Launch is planned for late 2005. As a result of 5-year design lifetime, NPP will provide data past the planned lifetime of EOS Terra and EOS PM and into the expected launch of the first NPOESS satellite. The proposed NPP mission is currently in the formulation phase.
The first merged NPOESS satellite is expected to be available for launch in the latter half of the decade, approximately 2008, depending on when the remaining POES and DMSP program satellite assets are exhausted. NPOESS will provide significantly improved operational capabilities and benefits to satisfy the nation’s critical civil and national security requirements for space-based, remotely sensed environmental data. NPOESS will deliver higher resolution and more accurate atmospheric and oceanographic data to support improved accuracy in short-term weather forecasts and warnings and severe storm warnings, as well as to serve the data continuity requirements of the climate community for improved climate prediction and assessment. NPOESS will also provide improved measurements and information about the space environment necessary to ensure reliable operations of space-based and ground-based systems and will continue to provide surface data collection and search and rescue capabilities.
NPOESS Instruments. The NPOESS satellites will carry six instruments designed to revolutionize weather forecasting and climate research:
1. Visible/infrared imager/radiometer suite (VIIRS). This sensor is arguably the most important in the entire NPOESS blueprint. It will spot smoke from forest fires, ash from volcanoes, and the rain bands of hurricanes. Images from VIIRS will show up on the nightly news and the Weather Channel. VIIRS will replace the advanced very-high-resolution radiometer (AVHRR) on the existing POES satellites. VIIRS will divide light into 22 channels, compared to six for AVHRR.
2. Conical microwave imager/sounder (CMIS). The advantage of CMIS is that it can see through clouds. It will detect microwave radiation emitted from the surface of the ocean and from the atmosphere. It will replace the special sensor microwave imager on DMSP and the microwave imager on NASA’s TRMM satellite.
3. Crosstrack infrared sounder (CrIS). CrIS is the primary instrument for measuring the temperature, moisture, and pressure of the atmosphere. It will replace the high-resolution infrared sensor on POES.
4. GPS occultation sensor (GPSOS). GPSOS will measure the atmospheric refraction of radio signals from the GPS satellite constellation and from the Russian Global Navigation Satellite System.
5. Ozone mapping and profiler suite (OMPS). OMPS measures the vertical and horizontal distribution ofozone. It will aid studies of the seasonal ozone hole over Antarctica and the thinning ozone layer over the Arctic.
6. Space environment sensor suite (SESS). SESS measures particles in the upper reaches of the atmosphere that can damage satellites. It will measure neutral and charged particles, electrons, and magnetic fields, and the optical signatures of the aurora phenomenon.
The European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) has also joined the consortium and will provide the first European meteorological operational satellite in polar orbit, called METOP, in 2004. It is planned to carry many instruments provided by the United States and will provide early morning and late evening coverage. Initially three satellites are planned in this series (39,40).
AIRS. Advanced Infrared Sounder AMSU. Advanced Microwave Sounding Unit APT. Automatic Picture Transmission ATS. Applications Technology Satellite AVCS. Advanced Vidicon Camera System ATN. Advanced TIROS-N
AVHRR. Advanced Very High Resolution Radiometer
CDA. Command and Data Acquisition
CMIS. Conical Microwave Imager/Sounder
CrIS. Crosstrack Infrared Sounder
DOD. Department of Defense
DMSP. Defense Meteorological Satellite Program
EOS. Earth Observing System
ERBE. Earth Radiation Budget Experiment
ESA. European Space Agency
ESSA. Environmental Science Services Administration
EUMETSAT. European Organisation for the Exploitation of Meteorological Satellites
FAA. Federal Aviation Administration
GOES. Geostationary Operational Environmental Satellite
GPS. Global Positioning System
GPOS. GPS Occultation Sensor GSFC. Goddard Space Flight Center
GVHRR. Geostationary Very High Resolution Radiometer HRIR. High Resolution Infrared IPO. Integrated Program Office IR. Infrared
ITOS. Improved TIROS Operational System
MOUSE. Minimum Orbiting Unmanned Satellite of Earth
MRIR. Medium Resolution Infrared
MSA. Meteorological Satellite Activities
MSL. Meteorological Satellite Laboratory
MSS. Meteorological Satellite Section
MSU. Microwave Sounding Unit
NACCAM. National Coordinating Committee for Aviation Meteorology
NASA. National Aeronautics and Space Administration
NESDIS. National Environmental, Satellite, Data, and Information Service
NESS. National Environmental Satellite Service
NOAA. National Oceanic and Atmospheric Administration
NOMMS. National Operational Meteorological Satellite Systems
NOS. Nimbus Operational System
NPOESS. National Polar-Orbiting Operational Environmental Satellite System NPP. NPOESS Preparatory Project NWSC. National Weather Satellite Center
OLR. Outgoing Long-wave Radiation
OMPS. Ozone Mapping and Profiler Suite
POES. Polar-Orbiting Environmental Satellite
POMS. Panel on Operational Meteorological Satellites
SAR. Search and Rescue
SBUV. Solar Backscattered Ultraviolet
SESS. Space Environment Sensor Suite
SEM. Space Environment Monitor
SIRS. Satellite Infrared Spectrometer
SMS. Synchronous Meteorological Satellite
SOCC. Satellite Operations Control Center
SR. Scanning Radiometer
SST. Sea Surface Temperature
TIROS. Television Infrared Observation Satellite
TOMS. Total Ozone Mapping Spectrometer
TOS. TIROS Operational Satellite
TOVS. TIROS Operational Vertical Sounder TRMM. Tropical Rainfall Measurement Mission USWB. United States Weather Bureau UV. Ultraviolet
VIIRS. Visible Infrared Imager Radiometer Suite VTPR. Vertical Temperature Profiling Radiometer