ABSTRACT
Three important active microwave instruments — the altimeter, the scatterometer, and the synthetic aperture radar (SAR) — are considered in this chapter. Examples of each of these have been flown on aircraft. The first successful flight of these instruments in space was on board Seasat. Seasat was a proof-of-concept mission that only lasted for 3 months before the satellite failed. Although improved versions of these types of instruments have been flown on several subsequent satellites, including Geosat, Earth Remote-Sensing Satellite-1 (ERS-1), ERS-2, TOPEX/Poseidon, Jason-1, and Envisat, the general principles of what is involved and examples of the information that can be extracted from the data of each of them are very well illustrated by the Seasat experience.
