Polar Orbiting SatellitesThe world's first meteorological satellite, was launched from Cape Canaveral on April 1, 1960. Named TIROS for Television Infrared Observation Satellite, it demonstrated the advantage of mapping the 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.
TIROS was a polar orbiting satellite meaning the satellite orbited in a latitudinal motion which takes it over the north and south poles. Today, polar orbiting satellite round the Earth 14.1 times daily.
Since the number of orbits per day is not a whole number, the orbital tracks do not repeat on a daily basis. Currently in orbit there are morning and afternoon satellites passes, which provide global coverage four times daily.
The advantages to polar orbiting satellites are...
- Closer to the earth with an orbit of about 520 miles (833 km) above the surface.
- The closer orbit provided much more detailed images.
- Excellent views of the polar regions.
The disadvantages are that the satellite...
- Cannot see the whole earth's surface at any one time.
- The path of each orbit changes due to the earth's rotation so no two images are from the same location.
- Limited to about six or seven images a day since most of the time the satellite is below the earth's horizon and out of range of listening equipment.
Geostationary SatellitesThe first geostationary satellite was launched in 1966. Unlike polar orbiting satellite, geostationary satellites orbit at a much higher altitude of 22,236 miles (35,786 km). Positioned over the equator, the satellite completes one orbit of the earth in 24 hours.
The net result is the satellite appears stationary, relative to the earth. This allows them to hover continuously over one position on the surface.
Early geostationary satellites were "spin stabilized" meaning they maintained stability by rotating and therefore viewing the earth only about 10% of the time. Current satellite are stabilized now in a way that they always view 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.Geostationary satellite are the bread and butter satellites for the meteorologist. Their advantages are...
- They always located in the same spot of the sky relative to the earth.
- They view the entire earth at all times.
- They can record images as fast as once every minute.
- Since their view is always from same perspective, motion of clouds over the earth's surface can be computed.
- They also receives transmissions from free-floating balloons, buoys and remote automatic data collection stations around the world.
- There location at about 22,300 miles (35,000 km) in space, provides less detailed views of the earth.
- Views of the polar regions are limited due to the earth's curvature.