Discusses spaceborne radar sensors which allow all-weather, day or night high-resolution imaging of the earth's land and ocean surfaces. The newest of these systems is the synthetic-aperture radar (SAR) which can penetrate dry sands covering desert regions revealing ancient topography buried meters beneath the surface. A comparison of airborne and space radar techniques is given. The Seasat SAR and the shuttle imaging radar-A (SIR-A) sensors are almost identical. They consist of four major electronic subsystems-transmitter, receiver, power converter, and control logic. These sensors are also compared.