The GMS (Geostationary Meteorological Satellite) built by Hughes Space and
Communications Company (HSC) for Japan have provided uninterrupted monitoring of weather
conditions since 1977 over more than 65 million square miles of the Pacific Basin - about
one-third of the Earth's surface.
With Nippon Electric Company (NEC) Corporation of Tokyo as the prime contractor to
Japan's National Space Development Agency (NASDA), HSC was the major subcontractor
responsible for the development and integration of the spacecraft. The satellites were
built at HSC's Integrated Satellite Factory in El Segundo, Calif. The Japanese
Meteorological Agency (JMA) is the end user and is responsible for operations.
GMS collects and distributes weather data to other Asia Pacific countries and
contributes to weather forecast services in countries from Australia northward to China,
including Japan, Burma, Indonesia, Korea, Laos, Malaysia, Mongolia, New Zealand, the
Philippines, Taiwan, Thailand, Tibet, and Vietnam.
In addition, GMS is an important link in the World Weather Watch, described by
meteorologists as the most detailed study of the Earth's atmosphere ever attempted.
Approximately 145 countries contribute daily surface and atmospheric measurements to the
effort.
GMS-2 and GMS-3 were launched, respectively, 11 August 1981, and 3 August 1984, from
Tanegashima Space Center in southern Japan. Both were carried aloft by the Japanese N-2 Star-37E booster.
GMS-4 was launched from Tanegashima 6 September 1989, on the Japanese H-1 UM-129A (6 SO) rocket.
GMS-5 was launched from Tanegashima aboard the new Japanese H-2 + SSB booster on 18 March 1995. GMS-4 now
serves as a backup asset.
All satellites in the GMS series operate at 140° East longitude in geosynchronous
orbit 36,000 km above the equator in line with Japan.
The principal instrument on board all satellites in the GMS series is the visible and
infrared spin scan radiometer (VISSR), which is produced by Hughes' Santa Barbara Research
Center. The spacecraft body carries the VISSR and spins at 100 rpm, while the antennas are
despun and remain pointed toward Earth.
The spinning motion of the satellite carries the west-east scan. The north-south scan
is produced by the VISSR scan mirror, which steps approximately 0.008° with each
satellite revolution.
Visible spectrum information consists of reflected sunlight and is obtained when
Earth's surface is illuminated by the sun. Infrared spectrum information consists of heat
radiation from Earth's surface and cloud tops. Since this information contains very little
sunlight reflection, it can be obtained day and night. Extremely sensitive detectors,
which are kept cold by a radiative cooler, convert Earth's infrared radiation into analog
signals.
The VISSR senses radiation and produces images of Earth and its atmosphere one scan
line at a time, similar to the way television images are generated. About 2500 scan mirror
steps or line scans are required to make a full image of the portion of Earth's disk as
seen by the satellite. With its specially designed optical telescope and detectors, the
VISSR obtains a complete 20° by 20° scan, produces an image of the full Earth disk every
25 minutes, and transmits that image back to Earth as weather facsimile pictures, showing
different portions of the hemisphere. This enables meteorologists to identify, monitor,
and track cataclysmic weather events such as windstorms, heavy rainfall, and typhoons, and
to predict weather dangers long before storms reach densely populated areas.
Unlike its predecessors, which carried one infrared channel each, GMS-5 carries three.
Two perform the same function as the single infrared on the previous satellites. The third
determines atmospheric water vapor distribution.
Many aspects of weather that affect the daily lives of people exist for such relatively
short periods that polar-orbit weather satellites fail to observe them. However, the GMS,
from its stationary vantage point of constant observation, acquires almost instantaneous
information on rapidly changing weather patterns and regional weather phenomena.
GMS-2 through 4 also carry a space environment monitor, developed by NEC, which is used
to investigate energetic particle activity emanated by the sun and to assist in studying
the effect of extreme solar activity on Earth's telecommunications systems. The monitor
detects solar protons, alpha particles, and solar electrons.
GMS-5 carries an experimental payload to relay search and rescue UHF emergency beacons
and data from aircraft and ships in distress to land and sea rescue parties.
In addition to providing Earth images, the satellites serve as geostationary repeaters.
Weather data is collected from transmitters on the ground, on the high seas, and in
aircraft, and is distributed to meteorological centers. GMS also allows remote monitoring
of islands, oceans, mountainsides, and other such areas not equipped with weather
observation stations.
Data from collection platforms are placed in remote areas and on ships, buoys,
aircraft, and miscellaneous weather stations. The platforms are invaluable in regions
prone to natural disasters. For example, information collected from remote data buoys is
monitored to provide early warning of impending tidal waves. In colder climates, data is
used to track annual snowfall and predict water runoff in the spring. The platforms also
are used to measure water levels along riverbanks to assist with flood control.
.png)
