April 24, 2000
Q: What is the difference between a geostationary
and polar orbiting satellite?
A: NOAA's Geostationary Operational Environmental Satellites, or
GOES, circle the Earth in a geosynchronous orbit, which means
they orbit the equatorial plane of the Earth at a speed matching
the Earth's rotation. This allows them to hover continuously over
one position on the surface. The geosynchronous plane is about
35,800 km (22,300 miles) above the Earth, high enough to allow
the satellites a full-disc
view of the Earth. Because they stay
above a fixed spot on the surface, they provide a constant vigil
for the atmospheric "triggers" for severe weather conditions such
as tornadoes, flash floods, hail storms and hurricanes. When these
conditions develop, the GOES satellites are able to monitor storm
development and track their movements.
Complementing the geostationary satellites are two polar-orbiting
satellites known as Advanced Television Infrared Observation Satellite
(TIROS-N or ATN), constantly circling the Earth in an almost north-south
orbit, passing close to both poles. The orbits are circular, with an
altitude between 830 (morning orbit) and 870 (afternoon orbit) km,
and are sun synchronous. The circular orbit permits uniform data
acquisition by the satellite and efficient control of the satellite by the
NOAA Command and Data Acquisition (CDA) stations located near Fairbanks, Alaska,
and Wallops Island, Virginia. Operating as a pair, these satellites ensure that
data for any region of the Earth are no more than six hours old.
