In the 1970s, Jet Propulsion Laboratory engineers and scientists realized that the sensors they were developing for interplanetary missions could be turned upon Earth to better understand our home planet. In 1978, JPL built an experimental satellite that had mass of 2,300 kilograms (5,070 pounds) and was called Seasat.

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 June 26, 1978, 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.