In the 1970s, JPL engineers and scientists realized that the sensors they were developing for interplanetary missions could be turned upon Earth itself to better understand our home planet. In 1978, JPL built an experimental satellite called Seasat to test a variety of oceanographic sensors including imaging radar, altimeters, radiometers and scatterometers.
Seasat flight-tested four instruments that used radar to study Earth and its seas. Radars are useful tools because they can penetrate clouds, they operate in all weather conditions, and they provide their own illumination so they can function day and night. The radar instruments on Seasat measured the satellite's distance from the sea surface, measured near-surface ocean winds and took pictures using radar rather than light for illumination. Seasat also carried a visual and infrared radiometer that provided measurements that were used to judge the results of the radar instruments.
Seasat was launched on an Atlas Agena rocket from Vandenberg Air Force Base, California. Unlike launches of interplanetary spacecraft from Florida on eastward flight paths, launches from Vandenburg place the satellite in a north-south orbit that takes it close to Earth's poles. Seasat sent data to Earth for 106 days.
Many later Earth-orbiting instruments developed at JPL owe their legacy to the Seasat mission. These include imaging radars flown on NASA's Space Shuttle as well as such Earth-orbiting satellites and instruments as Topex/Poseidon, the NASA Scatterometer (NSCAT), QuikScat and the planned Jason 1.
Mass: 2,300 kilograms (5,070 pounds)
Science instruments: Radar altimeter, scanning multichannel microwave radiometer, microwave scatterometer, imaging radar, visual and infrared radiometer
Launch: June 28, 1978
At 25, Remembering a Trendsetting Seafaring Satellite (6/27/03)
20 years of Shuttle Imaging Radar (11/12/01)
