SECTION V: Weather and Environmental Satellite Systems

7-37 Overview
Introduction a. Analysis of weather, terrain and other environmental factors is a critical step in the Intelligence Preparation of the Battlefield (IPB). The impact of weather, environment and terrain on the conduct of military operations has been demonstrated throughout history. Knowledge of current weather and terrain in an area of operations along with accurate predictions of future conditions is a definite advantage. The use of aircraft, rotary and fixed wing, laser guided weapons, other sophisticated means of delivering precision weapons and night vision sights has made knowledge of local and target area weather conditions even more important. To be of value, weather, terrain and environmental information must be current and accurate. Such data can be difficult to obtain, especially in areas where access is limited due to military or political restrictions.
History of Weather Satellites b. Since the 1960's, a variety of satellites have carried instruments to gather data on the weather, terrain and environment that would be difficult, if not impossible, to acquire by other means. The types of instruments and their resolution have improved over the years. New technologies and manufacturing capabilities continue to improve sensors and for the data processing capability.
Weather and Environmental Satellites c. Weather and environmental satellites are similar in that they gather information about the nature and condition of the Earth's land, sea and atmosphere by remote sensing. They accomplish this task with sensors which observe the Earth in various discrete bands of the electromagnetic spectrum. They are different in that the systems are designed to observe different phenomena and have sensors which gather data in different spectral bands with different resolutions. When data from space systems is merged with that obtained from other ground and airborne sensors, resultant products are of significantly better quality than those produced from only one source.
Electromagnetic Spectrum d. The electromagnetic spectrum is divided into regions based on wavelength from short gamma rays to long radio waves having a wavelength of many kilometers. All objects transmit, absorb or reflect electromagnetic radiation. These characteristics are different for each type of material, therefore each has its own "signature". For example, very healthy vegetation has a strong reflectance of infrared light whereas unhealthy vegetation does not. Both types of vegetation , however, may appear to be the same shade of green.
Comparison with the Human Eye e. The human eye senses electromagnetic waves with a wavelength between 0.4 m to 0.7 m (1 m = 1 micron = 1 x 106 m = 0.0000001 m) which is visible light. Electronic sensors carried on weather and environmental satellites senses electromagnetic energy across a greater portion of the spectrum. Each sensor is designed to detect energy in a specific, narrow band of the spectrum. Multispectral sensors simultaneously image a scene in numerous electromagnetic bands ranging from visible light through thermal infrared. Multispectral sensors have a much larger dynamic range than photographic film, producing higher contrast between objects. Sensors output electronic signals that convert to digital data. Digital data can be processed in unique ways. The full dynamic range of the output from the sensors can be digitized and recorded or transmitted to a processing station. Then, data from sensors are assigned shades of gray or combinations of red, green or blue so that a human eye can see a picture. The resultant image can look significantly different than a normal visible image of the same area. Trained analysts or special computer programs interpret an image.
7-37 Overview, cont'd
The Spectrum f.
Army's use of weather and environmental satellites g. In the past, the Army relied on other military services or agencies to provide products derived from the weather and environmental satellites. The Army is now developing and fielding equipment which is capable of processing data from these space systems and tailoring battlefield products to meet specific needs of Army tactical commanders.
7-38 Weather Satellites
Introduction a. The wideranging view afforded from orbit makes it possible to observe weather over a large area from an overhead perspective. Using satellites that are in geosynchronous orbits and others in sunsynchronous, polar lowearth orbits (LEO), it is possible to keep 100% of Earth almost constantly under observation.
Visual Sensors b. Visual sensors on the satellites take pictures of the cloud formations, land and water below. The size and shape of clouds can tell a meteorologist the type of weather in the area of interest. A series of pictures over time can reveal changes in the weather, the speed and direction of movement of storms and other aspects of the weather.
Infrared Sensors c. Infrared sensors on the satellites can provide digital data on the temperatures of the water, land and clouds in the frame of view. A black and white picture with numerous shades of gray is normally produced from the data. Each shade of gray represents a slightly different temperature. If colors are assigned to each shade of gray, the result is a highly detailed color picture similar to what is displayed on the commercial television weather reports.
Temperature of Atmosphere d. It is even possible to determine the temperature of the atmosphere at various altitudes by a technique called "atmospheric sounding." Sensors on weather satellites can detect the temperature of specific gases that make up the Earth's atmosphere. This data is integrated with data from other sensors. The combined data can then be analyzed using computer models of the atmosphere to determine a vertical profile of the atmospheric temperature. Analysis of this profile results in information on wind speed and direction and atmospheric pressure.
Computer Help e.. The advent of powerful computers capable of handling the immense quantity of satellite weather data has increased the understanding of how weather is created. It has also made it possible to extend the weather forecasting period to about 7 days.
Civil Satellites f. A variety of civil weather satellites in low Earth, polar orbits and geostationary orbits have been in operation for many years. The United States, Russia, Japan, China, Europe and others currently have civil weather satellites in operation. By international agreement the data sent from civil weather satellites is not encrypted and can be received and processed by anyone with the proper type of equipment. Weather data receivers and processors are available on the commercial market. The direct reception and processing of some of the high resolution data requires significant data processing capability. Although civil weather satellites have performed extremely well in space for long periods of time, they are not hardened against hostile action or nuclear effects.
U.S. Military Satellites g. Only the U.S. military has weather satellites that are hardened to enhance their survivability. They transmit encrypted data which cannot be used by anyone other than approved users who have been provided with the current COMSEC codes.
7-39 Polar Orbiting Weather Satellites
Introduction a. Sunsynchronous, polar orbiting, low Earth orbiting (LEO) weather satellites provide daily, full world coverage and higher resolution imagery than that available from geostationary satellites. Only the United States, Russia and China operate polar, low Earth orbiting, sun synchronous weather satellites. A sunsynchronous orbit is one in which the satellite passes over a particular part of the Earth at the same time every day.
U.S. Satellites b. The U.S. has two polar, LEO, sunsynchronous satellite weather systems:
  • Defense Meteorological Satellite Program (DMSP) provides weather data through all levels of conflict and disseminates global visible and IR cloud data and other specialized meteorological and oceanographic data to support DoD operations. DMSP is operated by the U.S. Air Force.
  • National Oceanic and Atmospheric Administration (NOAA) Advanced Television InfraRed Observation Satellite (Advanced TIROS). The NOAA/TIROS satellites provide images of cloud cover, snow, ice, and sea surface, plus temperature and moisture at various levels in the atmosphere for weather analysis and forecasting.
7-40 Defense Meteorological Satellite Program
Mission a. The mission of the Defense Meteorological Satellite Program (DMSP) is to provide an enduring and survivable capability to collect and disseminate global visible and infrared cloud data and other specialized meteorological, oceanographic and solar geophysical data, through all levels of conflict with the same survivability as the supported forces. DMSP has been accomplishing its mission for more than 15 years. In that time, more than 25 of the satellites have been successfully orbited.
Space Segment b. The operational DMSP constellation has two satellites in circular orbits at 833 km (450 nautical miles or 518 statute miles) altitude with an inclination of 98.7° and a period of 101 minutes. This is a polar, sun synchronous orbit. The DMSP satellites are in orbits which allows one to pass overhead in the early morning orbit and the other to pass overhead in the late morning. They have some antijamming capability and maneuverability to maintain correct orbital position and to aid in survival. All data transmitted from the satellite is encrypted, except when over the north and south poles. The current block of DMSP satellites is expected to last through 2003. The launch vehicles for this satellite is the Atlas rocket with a possible transition to the Titan IV in the near future. The DMSP satellites are launched from Vandenberg AFB, California.
Block 5D-2 Satellites c. The satellites currently in orbit are the Block 5D2 versions. The Block 5D2 is a prototype of the TIROS satellite. Each is a fivesided boxlike structure in which four of the five sides are equal in size, while the fifth side is wider and contains the earthviewing sensors. A large solar power panel is attached to one end of the spacecraft which it rotates once each orbit so that it is always oriented toward the sun during the daylight portion of the orbit.
Satellite Sensors d. The satellites carry a wide variety of sensors to produce high quality visible and infrared images and to provide measurements of atmospheric vertical temperature and moisture, ion and electron density, high energy particles, precipitating electrons and other parameters of the ionosphere. The primary sensor is the Operational Linescan System (OLS). The OLS is a two channel radiometer which consists of a Cassegranian telescope with elements for visible and infrared viewing. A set of relay optics separates the sensed wavelengths and fields of view for various detectors. The swath width of each scan is 2960 km (1600 nm). The OLS uses counteracting springs and a pulsed motor to drive the scanning optics across the field of view. The aperture size is dynamically altered to reduce the angular instantaneous field of view as it nears the edge of each scan. This results in imagery with nearly constant crosstrack resolution. Unlike other meteorological satellites, DMSP provides imagery at the edge of the swath that almost matches the quality of imagery directly below the satellite (at the nadir). The OLS calibrates, indexes and stores the data for transmission in either the fine or smoothed data modes. During daylight the resolution of the visible band data is 0.62 km and the resolution of the IR wavelength data is 2.8 km. The OLS has a photomultiplier tube which allows it to gather visible light data at night with as little as one quarter moon illumination. When the DMSP passes over a area at night the resolution of the visible wavelength is 3.5 km and the resolution of the IR data is 0.6 km. The swath width of each pass is 2, 963 km. Up to a quarter orbit of single channel, high resolution data are available through mission planning. The merging of the IR and visible channels in the lowresolution direct readout data transmission allows for comparable weather imagery between the night and day sides of the planet, even across the day/night terminator.
Combination of Sensors e. Up to twelve secondary sensors are carried on the current DMSP satellites to gather data on the threedimensional atmospheric temperature, water vapor, ozone soundings and the space environment. The combination of sensors not only allows for normal weather forecasting, but give the capabilities of monitoring wind and wave velocities, ground water content and ground level fog and smoke, and the space environment. On each orbit of a DMSP satellite, Earth rotates below it approximately 25° which is also the scan width of the OLS sensor. The combination of the satellite orbit, OLS scan width, and day/night imagery capabilities of the DMSP satellites makes a single satellite capable of obtaining almost total global coverage every 12 hours. On the average, the DMSP constellation of two satellites can capture 4 images per day of a given location. There are some locations on the equator that do not get imaged.
7-40 Defense Meteorological Satellite Program, cont'd
Sensors and their Applications f. This chart shows the full list of sensors, their applications and other information.
Data Transmission Rate g. The data transmission rate from the DMSP satellites has been modified to allow the use of smaller antennas. The S10 satellite, launched in December, 1990, was the first to include the capability to transmit data to a smaller tactical terminal.
Block 5D-3 Satellites h. The followon to the Block 5D2 spacecraft is the Block 5D3. The 5D3 series, satellite numbers S16 through S19, incorporates several improvements over the 5D2 spacecraft, including:
  • Increased satellite length to extend payload capacity.
  • Increased design life from 4 to 5 years.
  • Titan II Expendable Launch Vehicle (ELV) compatibility.
  • Improvements in existing payload sensors.
7-40 Defense Meteorological Satellite Program, cont'd
Ionospheric Disturbances i. Some of the new sensors will allow forecasting of space weather by monitoring the ionosphere, which affects ground to satellite communications and overthehorizon communications and radar. Readings from the new sensors will be beamed to the future Space Forecast Center, now being built at Falcon AFB, Colorado. Using computer analysis, Air Weather Service forecasters will be able to track the progress of ionospheric disturbances and predict what geographical locations will be affected.
Design of DMSP j. The Air Force has begun a complete redesign of the DMSP satellite to permit continued expansion of weather support. The new satellites will be DMSP Block 6. To ensure compatibility with today's data, Block 6 will provide the same quality data that will be provided by the 5D3 system at the same or less cost. Additionally, to ensure the ability to cost effectively use future instruments and capabilities which will be developed to meet Memorandum of the Joint Chiefs of Staff (MJCS) requirements, flexibility and extendibility will be designed into the system from the beginning when full advantage can be gained from cost savings. The Army has provided an Army annex which defines the Army's requirements for future DMSP satellites to the current DMSP System Operational Requirements Document (SORD).
Control Segment k. The DMSP control segment conducts all mission planning, generates real time and stored program commands, provides computer memory uploads, and recovers and relays mission data to users. It also handles telemetry acquisition, processing, analysis and the necessary communications between control sites.
Control Sites l. Control sites are the MultiPurpose Satellite Operations Center located at Offutt AFB, Nebraska, the Fairchild Satellite Operations Center (FSOC) at Fairchild AFB, Washington, and communications equipment located at various sites around the world.
Multi-Purpose Satellite Operations Center m. The MultiPurpose Satellite Operations Center (MPSOC) is responsible for monitoring satellite launch, conducting early orbit checkout and resolving satellite anomalies. It provides routine update and validation data of all onorbit flight software images. The MPSOC communicates with DMSP satellites by sending messages over domestic communications satellites to the Fairchild Satellite Operations Center and some of the Air Force Satellite Control Network sites for relay to satellites.
FSOC n. The FSOC has primary responsibility for the control segment. It conducts mission planning, real time command and control, coordinates scheduling and resolves conflicts. It has two dedicated antennas to contact the DMSP satellites. It relays data to Air Force Global Weather Central at Offutt AFB, Nebraska, and the Navy's Fleet Numerical Oceanography Center in Monterey, California.
Thule Tracking System n. The Thule Tracking Station at Thule Air Base, Greenland has three antennas to transmit commands to the DMSP satellites and receive DMSP mission data. The Thule Tracking Station is able to contact each DMSP satellite on each orbital pass over the North Pole. Other control segment ground stations are located in Hawaii, New Hampshire, Colorado and California.
User Segment o. The biggest DMSP data users are Air Force Global Weather Central (AFGWC), and the Navy's Fleet Numerical Oceanography Center (FLENUMOCEANCEN).
Environmental Products p. AFGWC receives data from DMSP and other meteorological satellites processing it on main frame computers to produce environmental products. AFGWC constructs and maintains the most comprehensive meteorological database. More than 118,000 weather observations are gathered daily from space, air, and ground sensors and are merged in a computerized database to construct and constantly update a worldwide model of the atmosphere. The model can project future atmospheric changes with a high degree of accuracy. AFGWC provides direct support to the President, special strategic programs, national command authorities, DoD, unified commands, all major air commands, staff weather teams supporting the Army, and many other government agencies.
Useage q. The FLENUMOCEANCEN receives and processes DMSP visible, infrared and microwave imagery and distributes products to the Navy's operational forecasting community on shore and afloat. Both AFGWC and FLENUMOCEANCEN send data, messages, facsimile and other products to DoD organizations throughout the world.
7-41 TIROS
Introduction a. The mission of the Television InfraRed Observation Satellites (TIROS) is to provide images of cloud cover, snow, ice and sea surfaces plus data on temperature and moisture at various altitudes in the atmosphere for weather analysis and forecasting. TIROS is operated by the National Oceanic and Atmospheric Administration, an agency of the U.S. Department of Commerce. The first of the NOAA weather spacecraft, TIROS 1, was launched from Cape Canaveral on April 1, 1960. Since then, more than 20 other TIROS satellites have been successfully launched into orbit. The current TIROS constellation consists of three satellites orbiting at 880 km altitude with an inclination of 99/. The design life of each satellite is approximately 2 years but many have operated longer.
Space Segment b. The TIROS satellites have a number of sensor systems which perform different functions. TIROS's main imaging system is known as the Advanced Very High Resolution Radiometer (AVHRR). A suite of sensors known as the TIROS Operational Vertical Sounder (TOVS) performs the same function as the atmospheric sounder in the GOES VAS system. These sensors provide data on weather and also measurement of sea surface temperatures. TIROS also has a Space Environmental Monitor (SEM) and is part of the Search and Rescue (SARSAT/COSPAS) network. The satellite continuously transmits data on the area below it and also records data to be played back on command from ground controllers. This allows the satellite to collect data on remote areas.
Orbits c. Each satellite orbits the Earth 14.1 times per day. This allows each satellite to image almost every point on the equator two times per day (once during the day and once at night). Geographic locations at higher latitudes are imaged three to four times per day, though the location may be on the edge of the scan of the additional passes where the resolution isn't as good. Thus, the whole constellation is guaranteed to give four good images of every location on Earth every day, except for a very few points on or near the equator. The satellites cross the equator at 7:00 a.m. and 2:00 p.m. and the times of the night images are around 12 hours later.
AVHRR d. The Advanced Very High Resolution Radiometer (AVHRR) measures clouds over the ocean and land in 5 visible and nearIR bands. The resolution is about 1.1 km at nadir and about 4 km at the edge of the scan which is about 2700 km wide. This provides 25° longitude of surface coverage within the scan width, with the central 15° providing the most useful data. Imagery from the AVHRR on each spacecraft is directly available to users with appropriate receivers. The imagery is transmitted in two operational modes. The first is direct readout of any two of the five spectral bands to ground receiving stations of the Automatic Picture Transmission (APT) class at 4 km resolution. The second mode is direct readout of all five spectral channels to ground receiving stations of the High Resolution Picture Transmission (HRPT) class around one km resolution.
7-41 TIROS, cont'd
Sensors and Instruments e. The list of sensors carried on the TIROS spacecraft, the applications and other characteristics are shown below. Future TIROS spacecraft will carry improved instrumentation to give broader capabilities. Changes will be made to the AVHRR channels which will allow it to better differentiate between ground features and weather features. The improved imager will provide a more useful indication of the "vegetation index" or "greenness", of an imaged region. Another change will allow enhanced determination of cloud cover versus snow and ice cover. The imager will also have improved sea surface temperature measurement capability.
Control Segment f. The Command and Data Acquisition (CDA) stations at Wallops Island, Virginia and Gilmore Creek, Alaska receive recorded and direct readout environmental data from the satellites. A receive only CDA station is also set up in Lannion, France at the Centre National d'Etudes Spatiales (CNES), France's national space center. The data are then sent to the NOAA satellite operations control center (SOCC) at Suitland, Maryland, via a communications satellite relay. HRPT is also received in Redwood City, California and Honolulu, Hawaii. Data are also relayed to the AFGWC to supplement the weather information provided by the DMSP data.
User Segment g. The Wraase weather receiver and other commercial weather receivers can receive TIROS APT transmissions. The Army uses TIROS data for both current weather determination and forecasting to support operations. The TIROS satellites provide data which enhances that provided by geostationary weather satellites. They also provide weather data of the polar areas not covered by geostationary satellites. It is also possible to receive data from civil weather satellites that are operated by other countries.
7-42 Other Countries
METEOR (Russia) a. The Soviet Union operated multiple Meteor weather satellites in low Earth orbit for many years. Russia has continued the Meteor weather satellite program. As many as five Meteor satellites are maintained in 900 km high orbits with an inclination of 81.2°, in a variety of orbital planes. Meteor satellites provide sensor data which is used for meteorological observations, measurement of sea surface temperatures, extent of sea ice and snow cover and data on the condition of vegetation in the field of view. A scanning telephotometer transmits infrared images as the satellite pass overhead. No encryption is used, therefore anyone with the proper receiver can receive the data The resolution is about 2 km with a swath width of about 2,000 km.
FENG YUN (China) b. China launched it's Feng Yun 1B weather satellite in September 1990. It is in a sunsynchronous polar orbit with an altitude of 830 km. The satellite has four sensors in the visible light band and one in the infrared band. The highest resolution is about 1 km. Each image covers an area about 1,600 km wide (eastwest) and 3,200 km long (northsouth). It continuously transmits data in analog format for Automatic Picture Transmission (APT) and in digital format for High Resolution Picture Transmission (HRPT). These signal formats are compatible with U.S. Tiros satellites, therefore, receivers capable of receiving TIROS data can also receive Feng Yun data.
7-43 - Geostationary Weather Satellites
Introduction a. Another group of weather satellites are maintained in geostationary orbit to provide a continuous watch of the weather on the Earth below them. Each geostationary weather satellites is able to continuously scan approximately one third of the Earth, collecting visual and IR data. The United States, Europe, Japan and India operate geosynchronous weather satellites. The Geostationary Meteorological Satellite (GMS), owned by Japan, provides coverage for the western Pacific. Europe's Geostationary METEOSAT, owned by the European Space Agency (ESA), provides coverage for the eastern Atlantic, Europe and central Africa.
Geostationary Operation Environmental Satellite (GOES) (US) b. The Geostationary Operational Environmental Satellites (GOES) are operated by the U.S. National Oceanographic and Atmospheric Administration (NOAA). GOES is a series of meteorological geostationary orbiting satellites that provide weather prediction data for the western hemisphere and particularly for the U.S. GOES imagery is accessible to over 10,000 ground stations in 120 nations and provides continuous storm tracking, cloud analysis, surface temperature mapping, data of floods, rain, snow, pollution, and solar flare activity.
Satellite Statistics c. GOES 1 was launched from Cape Canaveral on October 16, 1975. Since then, six other GOES satellites have been launched, the latest being launched on February 26, 1987. The GOES satellite is cylindrical with a diameter of 7 feet (ft) and a height of 12 ft. Being spinstabilized, it has a despun antenna mount platform for improved data transmission. External solar cells provide a maximum of 320 watts of power.
7-43 - Geostationary Weather Satellites, cont'd
Orbit d. The GOES system is meant to be a constellation of two geostationary satellites over the equator, one at 135° west longitude (GOESWest) and the other at 75° west longitude (GOESEast). Due to a premature failure of the imager on GOESEast and due to delays in the development of the followon to the GOES system, GOES 7 is the only fully operational GOES in orbit. GOES 7 is positioned at approximately 123° west longitude. To cover the Atlantic Ocean and eastern U.S., the European METEOSAT 3 weather satellite was repositioned to 50° west longitude. METEOSAT 3 provides good imagery but does not have an atmospheric sounder.
Equipment e. GOES 7 is equipped with a Visible and Infrared Spin Scan Radiometer (VISSR) Atmospheric Sounder (VAS), which simultaneously provides twodimensional images of the Earth in the visible light spectrum at . 9 km resolution, thermal infrared spectrum at 6.9 km resolution, and produces vertical sounding profiles of water vapor content, carbon dioxide content, and temperature. The satellite produces a 120° cone of usable imagery, 60° north, south, east, and west of the nadir, though the satellite can actually image the full disc of Earth. GOES 7 has a Space Environmental Monitor (SEM) Subsystem, which monitors the solar wind and environment around the satellite.
VAS Measurements f. VAS measurements are transmitted at a high data rate from GOESEast directly to the NOAA Command and Data Acquisition station (CDA) at Wallops Island, Virginia. Space Environmental Monitor (SEM) data transmission is received by the Environmental Research Laboratory (ERL) at Boulder, Colorado. Visible and IR data of the full earth disc are reformatted, calibrated, and gridded at the CDA station and immediately retransmitted to the GOES satellites at reduced data rates, called stretched VISSR. The satellites then broadcast the stretched VISSR in nearreal time which is received by NOAA's National Environmental Satellite, Data, and Information Service center (NESDIS).
Weather Facsimiles g. NESDIS, in Suitland, Maryland, prepares weather facsimile (WEFAX) images. WEFAX is only a small subset of available GOES data. These WEFAX images are then broadcast according to a schedule via both GOES satellites. GOES WEFAX broadcasts include METEOSAT and GMS images. In addition, GOES WEFAX includes data collected by earthbased sensors so that they are available to users on a timely basis. Although WEFAX is not realtime data, it is usually less than 30 minutes old. The advantage of WEFAX is that processing of raw data from the satellite has already been done in a central location using powerful computers. Users only need relatively inexpensive WEFAX receivers. The Army uses GOES WEFAX data for forecasting weather. The Wraase weather receiver, receives the WEFAX broadcast. This provides the Army with weather imagery of much of the world. Each Air Force Staff Weather Officer (AF SWO) supporting Army commands has been issued the Wraase receiver by the Army. Global Weather Central (GWC) also utilizes GOES data. The data transmitted from the satellite is not encrypted and can be received by anyone with the proper receiver.High quality, timely products are available via telephone lines for commercial users who sign a contract with NOAA. This is called GOESTAP.
7-44 GOES Next
Overview a. GOESNext, an entirely new satellite design, will be able to better monitor hurricanes, weather fronts, and other meteorological phenomena. The program is having problems with cost overruns and schedule delays which could delay the deployment of the GOESNext satellite.
Introduction a. METEOSAT weather satellites are owned and operated by Eumetsat, a consortium of 16 European countries. The control station for METEOSATs is located at Darmstadt, Germany. METEOSATs are launched into a geostationary orbit at 0° longitude where they can obtain the best data for European weather conditions. METEOSAT 4 is the current satellite in use. METEOSAT 5 was launched in March 1991 and is an onorbit spare.
Meteosat Sensors b. METEOSAT sensors are similar to GOES. Sensor data is transmitted to the Data Acquisition, Telemetry and Tracking Station at Oldenwald, Germany which relays the data to the Meteosat Ground Computer System . The images are processed, coastlines and latitude/longitude grid lines are superimposed. The processed image is then transmitted to the METEOSAT satellite which broadcasts the image is a conventional WEFAX format, similar to other geostationary weather satellites. Two other channels on the satellite transmit digitized facsimile and other meteorological reports. is provide to users in a similar format.
Area of Coverage c. The area of coverage of a typical METEOSAT is shown below. Coverage of northern Europe is limited by the curvature of the Earth. The data is an excellent supplement to the data provided by the higher resolution polar orbiting weather satellites because of the broad area coverage and the different sensors. METEOSAT images were used extensively during Operation DESERT SHIELD/STORM although Saudi Arabia is near the edge of coverage. METEOSAT provides images of the Earth every 30 minutes. In August 1991, METEOSAT 3, was repositioned to 50° W longitude to replace GOESEast which had failed. METEOSATs transmit weather data in formats that are very similar to GOES. Receivers capable of receiving GOES data can also receive METEOSAT data.
7-46 INSAT (India)
Introduction a. India operates INSAT geostationary multipurpose satellites. These unique satellites carry telephone, and television transponders along with weather sensors. The satellites are controlled from the INSAT Master Control Facility at Hassan, Karnataka, India.
Sensors b. The sensors are similar to those on a GOES. In compliance with the international agreement on weather satellites, the data are not encrypted, however the signals from the satellite are transmitted on a narrow spot beam to the Delhi Earth Station. The spot beam limits reception of the data to a small area. India did not share data from this satellite until 1991 and then the data was 3 years old. The probable reason for the narrow transmission beam and the lack of sharing of the data is to keep certain neighboring countries from getting the information. The data is relayed to the Meteorological Data Utilization Centre in New Delhi where the data is processed. The meteorological products are then relayed through an INSAT satellite to 22 Secondary Data Utilization Centers throughout India.
Coverage c. As can be seen from the picture below, the area of coverage of INSAT satellites is very good for the Middle East, the Indian Ocean, the Indian subcontinent and Southeast Asia. INSAT would have provided better weather coverage during Operation DESERT SHIELD/STORM but the signals could not be received by units in Saudi Arabia.
7-47 Geostationary Meteorological Satellite (GMS)
Introduction a. Japan's Geostationary Meteorological Satellites (GMS) are in geostationary orbit at 140°E longitude which allows the satellite to image the Pacific Basin. The GMS satellites are controlled by the Meteorological Satellite Centre of the Japan Meteorological Agency.
Sensors b. A list of the sensors carried on GMS4 is below.
Coverage c. GMS data are received at the Command and Data Acquisition Station in Hatoyama, just north of Tokyo. The data is relayed to the Data Processing Centre where Stretched VISSR and WEFAX images are created. These are then retransmitted to users through the GMS. The products are also relayed to NESDIS in Maryland where NOAA uploads them as WEFAX on the U.S. GOES weather satellites. Data from these satellites is transmitted in formats similar to GOES and METEOSAT.
GOMS (Russia) d. The U.S.S.R. agreed to provide a satellite constellation known as Geosynchronous Operational Meteorological Satellite (GOMS). Russia has continued the program, however, the launch date is uncertain. This constellation will consist of three satellites at 76° E, 166° E, and 342° or 346° E longitude with a possible inclination of 40° 50°. This inclination would allow the satellite to gather data much farther to the north than a geostationary satellite is able to do. Since so much of Russia is in the far north, this is the only way to have an effective system that meets their needs.
China e. China's publicly announced plan for becoming a part of the global Earth Observing System Initiatives included a geostationary platform. It could help fill some of the gaps in global coverage left by the unavailability of data from India's INSAT satellites.
7-48 Weather Satellite User Segment
Introduction a. There is a great variety of weather satellite receivers available through military and commercial channels. At the low end, some receivers are simply shortwave receivers with a facsimile machine attached. They receive WEFAX transmissions but do not have any data storage nor processing capability. On the high end are complete, complex and expensive terminals which receive and process the large volume of high resolution data directly from the weather satellites, store it, process it, enhance it, combine multiple images and produce very high quality products.
DMSP Receivers b. The Air Force has 18 "tactical" DMSP receiver terminals of three types. The term "tactical" means they support users rather than control segment. There are two AN/FMQ14 fixed station terminals. There are six AN/TMQ37 terminals. They were originally housed in 40foot trailers. Although the AN/TMQ37 was originally designed to be deployable by C5 aircraft, most have been moved into fixed facilities. The Air Force has ten AN/TMQ35 terminals, each in an 8 x 8 x 20foot standard shelter van, called Mark IV vans. Mark IV vans were designed to transported by C130 aircraft. Six were converted to semi-permanent facilities leaving four transportable Mark IV vans. As a DMSP satellite passes within view of the terminal, data is received, stored, and processed. Realtime hardcopy weather imagery can be produced in the van or the image can be transmitted to a remotely located high quality facsimile machine.
Marine Corps c. The Marine Corps has twelve transportable Mark IV vans which consist of an AN/TMQ35, an antenna pedestal and mobilizers for the van which allow it to be towed to an operational site. The AN/TMQ35 can provide a film hard copy of DMSP imagery or transmit it as a facsimile to other weather detachments.
Navy d. The Navy has installed AN/SMQ10 and 11 terminals at fixed shore facilities and on aircraft carriers. The AN/SMQ11 Shipboard Receiving Terminal is a complete meteorological terminal that receives, processes, and displays real time DMSP data, as well as TIROS and GOESWEFAX data. The AN/SMQ11 has two electronic equipment cabinets along with an antenna pedestal assembly. The system produces an 8X16 " drysilver film image which covers an area of 3000 by 6000 km. An image expansion capability produces "mural size" images nearly 3 by 5 ft, which provide excellent image definition. The Navy is planning to install an additional eighty shipboard and shore terminals.
Army e. The Army currently does not have any DMSP terminals. The Army receives products, such as forecasts and weather charts, through supporting Staff Weather Officers (SWO).
Rapid Deployment Imagery Terminal (RDIT) f. The DMSP Program Office is pursuing the testing, evaluation, and selection of offtheshelf high resolution systems to receive the DMSP fine data format. The RDIT weighs about 500 pounds. The terminal produces both video and printed images using data from the Operational Linescan System on the DMSP satellites. The terminal will receive the full DMSP data stream and will process the imagery and the special DMSP sensor data and may handle some civil weather satellite data.
7-48 Weather Satellite User Segment, cont'd
Integrated Meteorological System (IMETS) g. The Army is developing the Integrated Meteorological System (IMETS) to provide Army commanders at all echelons with an automated tactical weather system. The system has the following attributes:
  • Tactical automated weather data receiving, processing and dissemination system.
  • Receives surface, upper air, satellite and other weather data.
  • Integrates weather data into the commander's planning process.
  • Provides forecasts and decision aids to other systems.
  • Uses ATCCS common hardware and software.
  • Compatible with Army tactical communications systems.
  • Compatible with USAF weather data distribution systems.
Army Fielding of IMETS h. The Army plans to field 42 IMETS to EAC, Corps, Divisions, Separate Brigades and Special Operations Forces. Initially, the system will use a Wraase weather receiver to receive data from civil weather satellites. The Small Tactical Terminal will be installed when it becomes available. This will meet the Army's requirement for a mobile, modular, tactical automated weather data receiving, integrating, processing, and dissemination system to provide weather and environmental effects forecasts, observations, and decision aid information to commanders at all echelons where AF weather teams provide support to the Army.
DMSP Small Tactical Terminal (STT) i. The DMSP Program Office, with input from the Army, is developing a Small Tactical Terminal (STT). It will allow the full use of civil and defense satellite imagery.
7-49 Commercial Weather Satellite Receivers
Introduction a. There are many types of commercial weather satellite receivers manufactured around the world. The capabilities of these receivers range from simple, inexpensive receivers which display low resolution WEFAX data without any processing capability to expensive receivers which can store and process high resolution data.
WRAAS Weather Satellite Receiver b. The Wraase weather receiver receives only WEFAX and APT images from the U.S., Russian, Japanese, and European civil weather satellites. It cannot receive other sensor data transmitted by the civil weather satellites that can provide information on winds, atmospheric temperatures and moisture content. DMSP data cannot be received. The Wraase receiver is about twice the size of a video cassette recorder (VCR). It comes with two black and white display CRTs and a small video printer which provides weather images. Up to eight images can be stored in temporary memory and played back in sequence. Not only does the Wraase receiver allow easy reception of geostationary and polar orbiting commercial weather satellite transmissions, but its size makes it easily deployable.
DESERT SHIELD/STORM c. Army forces deployed to Saudi Arabia for Operation DESERT SHIELD/STORM used Wraase receivers to receive METEOSAT and U.S. and Soviet polar orbiting weather satellite data. Two were integrated into Forces Command (FORSCOM) Automated Intelligence Support Systems (FAISS) to allow additional processing of weather images. A commercial Weathertrac system was connected to the FAISS to digitize, enhance, and manipulate the imagery. Although METEOSAT provided the lowest resolution imagery, it was available every 30 minutes. The Army 30th Engineer Battalion (Topographic) supporting ARCENT regularly incorporated DMSP imagery provided by the Air Force into its battlefield environment analysis products.
Dissemination to Unit d. Dissemination of weather products to tactical units below division level was difficult. Problems resulted from the volume of data, the lack of display equipment and a loss in resolution during conversion from analog to digital format for transmission over Army communications equipment and then reconversion to analog data for display by the recipient.
7-50 Geographic Remote Sensing Satellites
Introduction a. Weather monitoring is only part of the effort required to monitor the environment of Earth. The other part is geographic remote sensing. Geographic remote sensing gives a unique view of the Earth. Remote sensing by satellites, especially multispectral imagery, provides critical information that is of immediate military value. Geographic remote sensing satellites can provide data on man made and natural terrain features, coastal areas and the oceans. This can be used to update maps, analyze routes and avenues of approach, identify water source, asses vegetation, detect contamination, and other uses that are of importance to the military. Remote sensing has even helped researchers track the spread of diseases and viruses.
Other Countries b. Numerous countries have developed satellite systems to gather data on Earth's environment from space. The U.S. Landsat, French SPOT, Japanese MOS and JERS1, Indian IRS, Russian ALMAZ and RESURSF, and Europe's ERS1 are all capable of providing a variety of imagery and other data ranging from 5 to 80 meter (m) spatial resolution. China has expressed interest in developing its own earth resources satellite. Canada plans to launch a radar remote sensing satellite in 1994. Brazil has also considered developing a remote sensing satellite.
LANSAT (U.S.) c. Landsat 1 was launched on July 23, 1972. The satellite, which was expected to function for about 1 year, finally ceased operating early in 1978. Since then, four other satellites have been launched with progressively more versatile and sophisticated capabilities.
Landsat Constellation d. The current constellation consists of two satellites, Landsats 4 and 5. Landsat 4 was launched in July 1982 and Landsat 5 was launched in March 1984. They are in sunsynchronous orbits at 705 km altitude and 98.2 inclination with ground tracks of 185 km width. This allows a satellite to pass within sensor range of every location on Earth at least once every 16 days. Landsat 6, with capabilities similar to Landsat 5, is scheduled for launch in early 1993.
Control e. Landsat satellites are controlled from the Spacecraft Operations Control Center in New Jersey through antennas located at NOAA's Gilmore Creek site near Fairbanks, Alaska. Data is transmitted at a high rate to licensed data processing stations around the world.
7-50 Geographic Remote Sensing Satellites, cont'd
Sensors and Scanners f. Each satellite carries a Multispectral Scanner (MSS), a Thematic Mapper (TM) and a Return Beam Vidicon (RBV).
Multispectral Scanner g. The Multispectral Scanner collects data by continuously scanning Earth from west to east using an oscillating mirror, recording radiation in four different spectral bands in the visible and the nearIR regions with a resolution of 80 m. Bands 1 and 2 are in the visible wavelengths; bands 3 and 4 are in the nearIR portion of the spectrum. In order to present all of the bands in a fashion visible to the human eye, colors or shades of black and white are assigned to each band with the result of creating an image. As an example: band 1 detects green and could be shown as blue; band 2 detects red and could be shown as green; either band 3 or band 4, both of which detect separate bands of IR light, can be used in the construction of an image with bands 1 and 2 and could be shown as red.
Thematic Mapper h. The Thematic Mapper receives solar reflected energy covering the entire visible spectrum and the near, shortwave, and thermalIR spectrums using 7 bands. In this respect, the Thematic Mapper sensor has the greatest spectral discrimination of any sensor platform currently in orbit. This capability allows greater discrimination among a large number of terrain feature types. Six of these bands provide at least 20 basic combinations and 120 permutations for a threeband color image. Each of these combinations has its own unique attributes. An optimum combination is a function of the intended application and a matter of personal band combination for imagery analysis.



Wavelength, µm



0.45 - 0.52

Senses bluegreen visible light. Maximum penetration of water which is useful for mapping in shallow water. Also useful for distinguishing soil from vegetation and deciduous from coniferous plants.


0.52 - 0.60

Senses green visible light. Matches green reflectance peak of vegetation. Useful in assessing plant vigor.


0.63 - 0.69

Senses red visible light. Matches chlorophyll absorption band. Useful in discriminating vegetation types.


0.76 - 0.90

Senses reflected near infrared. Useful for determining biomass content and for mapping of bodies of water which appear opaque.


1.55 - 1.75

Senses reflected midinfrared. Indicates moisture content of soil and vegetation. Penetrates thin clouds. Good contrast between vegetation types. Useful for differentiation between snow and clouds.


10.40 - 12.50

Senses thermal infrared. Can be used at night. Useful for thermal mapping and estimating soil moisture.


2.08 - 2.35

Senses reflected infrared. Wavelength coincides with absorption bands of hydroxyl ions in minerals. Combination of bands 5 & 7 used for mapping hydrothermally altered rocks associated with mineral deposits.
7-50 Geographic Remote Sensing Satellites, cont'd
Example i. For example, TM band 1, which detects energy within the blue region of the spectrum to a resolution of 30 meters, can be combined with the other visible light bands of the Thematic Mapper to produce a natural, true color image. Those regions of the spectrum invisible to the human eye are enhanced by false color imaging. The Return Beam Vidicon sensor was carried on early Landsat spacecraft. It has been replaced by the Thematic Mapper on current Landsats but some sensor data is available from archives.
Data Tramission j. Landsat data is transmitted at high speed from the satellites to fixed receiving and processing stations around the world. As a commercial system, only licensed ground stations can receive and process Landsat data.
Landsat Use k. Landsat is mainly used for terrain analysis and topographic mapping by DoD organizations. The satellites repeat their orbital path every 16 days, depending on cloud cover. In addition, the data must be processed on the ground, which normally takes about 15 days. The result is that data could be up to one month old, which eliminates Landsat as a primary intelligence source. In a crisis, such as DESERT SHIELD/STORM, limited amounts of data can be processed faster.
7-51 Other Country Weather Satellites
Systeme Probatoire d'Obserbation de la Terre (SPOT) (France) a. SPOT satellites are owned and operated by the Centre National d'Etudes Spatiales (CNES), a French governmental organization. SPOT 1 was launched in 1986. SPOT 2 was launched in January 1990. The satellites have the same mission as Landsat but have different capabilities. They are launched into a sun synchronous , 832 km high orbit with an inclination of 98.7°. The satellites repeat their ground trace every 26 days. In the panchromatic mode (black and white) visual images with a resolution of 10 meters is possible. The four band multispectral mode has a resolution of 20 meters. The resolution of SPOT images is higher than that of Landsat, however, Landsat images have more spectral bands. SPOT sensors can also provide stereo image data. SPOT data can be purchased in the commercial market. During Operation DESERT STORM, France implemented restrictions on the distribution of SPOT data to members or supporters of the coalition of allied forces, of which France was a member. The Army integrated SPOT and LANDSAT data which resulted in a significantly better product.
SPOT Sensors b.
Earth Remote Sensing Satellite (ERS-1) (Europe) c. The European Space Agency, a consortium of 13 European countries owns and operates the ERS1 satellite which was launched in July 1991. It is designed to produce images and other data on the ocean surface, ocean temperature, ocean bottom in shallow coastal areas, wave patterns, ice conditions, crop development and forest management. The Synthetic Aperture Radar (SAR) instrument is designed primarily to measure ocean wave length and direction but has also been able to detect ocean wave fronts and current shear.
7-51 Other Country Weather Satellites, cont'd
ERS Images d. When there is little wind on the ocean surface, the radar is able to provide images of the ocean bottom in shallow coastal waters. Such information is valuable in planning for amphibious landings. A scatterometer instrument can measure wind speeds on the ocean's surface. This can be helpful in weather prediction. The instrument has also produced good maps of different types of ice covering Antarctica. The high stability of the satellite platform allows images taken on different days to be superimposed more easily. Superimposing images of the same area taken at different times can make any changes easier to detect.
ERS Images e.
Marine Observation Satellite (MOS) (Japan) f. Japan launched its first Marine Observation Satellite (MOS1) in 1987. The launch of MOS1B followed in 1990. They were placed in a 910 km high orbit, inclined at 99.1° which provides a revisit time of 17 days. They were developed and operated by the National Space Development Agency (NASDA) of Japan. The satellites carry multispectral instruments which gather data on sea surface temperature and color, sea sediment, snow pack, vegetation, cloud distribution and atmospheric water content. The sensors carried on MOS1B are listed below. Although designed to support oceanography the system can provide useful information for topographers. A data collection System Transponder relays information transmitted from ocean buoys and automatic, unmanned remote weather stations.
7-51 Other Country Weather Satellites, cont'd
MOS Sensors g.
Japan Earth Resources Satellite 1 (JERS-1) h. The Japan Earth Resources Satellite (JERS1) is operated by Japan's National Space Development Agency (NASDA). It was launched in February 1992 into a low Earth polar orbit The revisit time is about one month. The satellite carries infrared optical sensors and a synthetic aperture radar (SAR). The SAR can see through clouds and fog with a resolution of 59 feet (18 m). SAR imagery is useful for studying geographic formations and may be helpful in the study of earthquakes, volcanoes mineral deposits and other geological information.
Indian Remote Sensing (IRS) Satellites i. The Indian Remote Sensing satellites were built by the Indian Space Research Organization (ISRO). IRS1A was launched in 1988 followed by IRS1B in 1991. Each satellite carries two imagers with a resolution of 117 feet (36 m) by 237 feet (73 m) across. The revisit time is 22 days. Neither satellite has any onboard data storage, therefore the satellite must be within lineofsight of the receiving station in order to provide any image data. This limits the satellites' ability to take images of other parts of the world and store them until an orbit passes over India. A receiving station at the National Remote Sensing Agency in Hyderabad, India processes the data from the satellites. The same station is licensed to receive data from Landsat and SPOT. It also receives data from civil polar orbiting weather satellites. India has not yet made data from these satellites available outside of India. The next satellite in the series, IRS1C, is scheduled for launch in 1994. It will carry a multispectral imager with a resolution of 33 feet (10 m).
Almaz (U.S.S.R./Russia) j. The Soviet Almaz 1A satellite was launched in March 1991. Russia assumed responsibility for its operation after the demise of the Soviet Union. It carried a synthetic aperture radar imager with a resolution of 50 feet (15 m) which could image geologic formations regardless of cloud cover. It was the first commercial radar satellite. Data from the satellite was transmitted to a ground station in Moscow for storage on magnetic tapes which were then provided to customers. Almaz Corporation, an American subsidiary of Space Commerce Corporation, is the worldwide marketing agent for Almaz data. Due to higher than normal solar activity, the Almaz 1A satellite's orbit was degraded rapidly. The satellite was destroyed reentering the Earth's atmosphere in October 1992. Russia has announced that it intends to place another Almaz satellite into orbit but no date has been announced.
7-51 Other Country Weather Satellites, cont'd
Resurs-F (U.S.S.R./Russia) k. The Soviet Union has launched numerous ResursF remote sensing satellites. Russia has continued the program. The satellites are launched into a low Earth polar orbit. The satellites are used for civil remote sensing photography. There are two models. One carries two long focus optical cameras, three multispectral cameras and a stellar camera. The other model carries only a multispectral camera and a stellar camera. The stellar camera takes pictures of the stars at the same time pictures of the Earth are taken to verify the satellite's location at the time of the Earth photo. At the end of the mission, usually about two weeks, the payload portion of the satellites is commanded to separate and reenter the Earth's atmosphere. A parachute deploys after reentry and the film canister is recovered for processing. The payload is usually refurbished and used in a later mission. Resolution of the multispectral photographs is about 5 meters. The apparent principal use is to monitor the condition of agricultural areas within Russia and other former Soviet republics. The Russians also sell some photographs on the commercial market if the images are not of areas they consider sensitive. Although the resolution is high, the data is difficult to integrate with digital data from other multispectral satellites since the only products are photographs (a form of analog data).
7-52 Use of Multispectral Data
Introduction a. Multispectral sensor data is used to discriminate or identify objects and features which often exhibit little difference in the visual range of light. The data from the sensors on the satellites is transmitted to ground stations capable of receiving, storing and relaying the data to users. Most MSI sensors generate large amounts of data that are transmitted at a high rate. This usually requires special, fixed receiving stations. In most cases, the data must be purchased in the commercial market. The raw data from the sensors must be processed before it is usable.
Army Landsat Purchase Groups b. To improve the Army's ability to acquire LANDSAT data, the Army has executed a memorandum of understanding (MOU) with the USGS EROS Data Center. With this agreement, the Army's Topographic Engineering Center (TEC) Terrain Analysis Center coordinates Army procurement of MSI. The memorandum also defines the Army purchase groups. They are:
  • Office of the Secretary of the Army and subordinate offices
  • Office of the Chief of Staff of the Army and subordinate staff
  • Training and Doctrine Command (TRADOC) and subordinate centers and schools
  • U.S. Army Materiel Command
  • Intelligence and Security Command
  • U.S. Army South
  • U.S. Army Western Command
  • U.S. Army Japan
  • Eighth U.S. Army
  • 1st Special Operations Command
  • U.S. Army Corps of Engineers
  • Health Services Command
  • Criminal Investigation Command
  • Military Traffic Management Command
  • Information Systems Command
  • Military District of Washington
Organizations within the purchase group can share data without having to pay an additional fee.
Image Processing c. The raw multispectral data is first processed to correct distortion from the curvature of the Earth, to orient the image to north and often to overlay a set of coordinates over the image. The data is also enhanced electronically so that contrast and detail are improved. The capabilities of computers and programs are important, however, imagery and terrain analysts are crucial part of the process of interpreting the images.
United States Army Multispectral Imagery Product Guide d. In June, 1990, the Intelligence and Threat Analysis Center (ITAC) prepared and distributed the United States Army Multispectral Imagery Product Guide. The guide is designed for Army planners and collection managers. It provides the essential information required for defining MSI requirements. The purpose of the product guide is to provide examples of the types of MSI products available to U.S. Army agencies.
TOPO e. The 30th Engineer Battalion (TOPO), with help from the Army Space Command (ARSPACE), prepared a lessons learned document based upon their support to Operation DESERT SHIELD/STORM. The "cookbook" type document lays out, stepbystep, what a tactical terrain unit must do to effectively and efficiently exploit MSI to support deployed forces.
7-52 Use of Multispectral Data, cont'd
ITAC MSI Exploitation f. At the HQDA level, the Intelligence and Threat Analysis Center (ITAC) is best equipped to exploit and produce MSI products for the Army. Their close association with the National Photographic Interpretation Center (NPIC) puts them in an excellent position to capitalize on that national asset for production of MSI products. The large, fixed operation allows them to effectively use minicomputers to support their exploitation effort. They produced image maps for use in support of Operation DESERT SHIELD/STORM. Additionally, they prepared digital products for tactical users to further exploit on smaller, personal computer systems.
FAISS g. The FORSCOM Automated Intelligence Support System (FAISS) has been distributed to selected FORSCOM G2 staffs and terrain teams. The FAISS greatly increases the ability of division terrain teams to produce MSI products.
Application of MSI h. MSI products are used to supplement and update military maps. They rarely replace military maps because they do not have sufficient resolution. Terrain analysts use MSI to gain information on geographic formations, natural barriers, soil conditions, moisture conditions, trafficability, and vegetation type and density. Intelligence analysts use MSI to assist in analyzing avenues of approach, amphibious landing sites, camouflage, identification of contaminated areas, crop conditions and identification of key terrain.
7-53 Geodetic Satellites
Introduction a. Geodetic satellites make it possible to survey the movements of the continents and utilize such information for investigating the phenomena of earthquakes and volcanoes.
U.S. Launch of ANNA 1B b. The U.S. launched its first successful geodetic satellite, ANNA 1B in 1962. It was put into an near circular orbit at 1077 to 1182 km altitude with an inclination of 50°. It carried three types of instruments for geodetic research. Since then, the U.S has successfully launched nine other geodetic satellites.
LAGEOS c. In 1976, the U.S. launched the Laser Geodynamics Satellite LAGEOS. This satellite is a sphere with hundreds of holes in the outer shell. In each whole is a laser corner reflector. A corner reflector is a special prism that reflects light back to its source regardles of the incident angle. Lasers on the ground direct a beam at the satellite. By measuring the time it takes for the laser beam to return to the transmission site and with precise knowledge of the satellite's position in space it is possible to measure locations with an accuracy of a few centimeters. This satellite has been extremely helpful in determining the movement of the Earth's crust. This is critical to measuring the movement of geographic faults, such as the San Andreas Fault in California. The satellite is expected to remain useful for about 50 years.
GEOSAT d. In 1985, the U.S. launched the GEOSAT geodetic satellite from Vandenberg AFB by an Atlas E rocket and sent into a circular orbit 800 km in altitude. The U.S. Navy operated the satellite until 1990. GEOSAT was equipped with a radar altimeter capable of approximately 8 inch resolution. The data was used to make ocean observations and can support map production. In June 1992, the Navy declassified all Geosat data of the area south of 30/ south latitude.