WEATHER SATELLITES Types

Satellite Types

There are two primary types of weather satellites in use:

Geostationary Satellites

Geostationary satellites (or geosynchronous satellites) orbit the equator at the same rate the earth spins, once per day. They orbit at a distance of 22,300 mi (36,000 km) above a fixed spot on the earth's surface. This positioning allows continuous monitoring of a specific region. GOES 9 (Geostationary Operational Environmental Satellite) is the latest in a series of GOES satellites, launched May 23, 1995.

Geostationary satellites measure in "real time", meaning they transmit photographs to the receiving system on the ground as soon as the camera takes the picture. A succession of photographs from these satellites can be displayed in sequence to produce a movie showing cloud movement. This allows forecasters to monitor the progress of large weather systems such as fronts, storms and hurricanes. Wind direction and speed can also be determined by monitoring cloud movement.

More detailed information on the GOES satellite series can be obtained from:

• The GOES Project

The geostationary satellite orbits at the same rate as the earth, so it remains above a fixed spot on the equator and monitors one area constantly.

Polar Orbiting Satellites

Polar orbiting satellites closely parallel the earth's meridian lines. They pass over the north and south poles each revolution. As the earth rotates to the east beneath the satellite, each pass monitors an area to the west of the previous pass. These 'strips' can be pieced together to produce a picture of a larger area.

Polar satellites have the advantage of photographing clouds directly beneath them. Geostationary satellite images of the polar regions are distorted because of the low angle the satellite sees the region. Polar satellites also circle at a much lower altitude (about 530 mi., 850 km) providing more detailed information about violent storms and cloud systems.

The polar orbiting satellite scans from north to south, and on each successive orbit the satellite scans a strip further to the west.