Earth resources research using the Shuttle Imaging Radar system

The Shuttle Imaging Radar (SIR) is an L-band synthetic radar that transmits and receives horizontally polarized microwave radiation. It was originally launched on the second Shuttle test flight (STS-2) in November 1981 with the antenna depression angle fixed at 43 deg. In this configuration, the radar system was referred to as SIR-A, and it collected more than then a million square kilometers of Earth imagery in a variety of areas situated between 38 deg north and south latitude. SIR-A data was optically recorded onboard the Shuttle, and it was subsequently correlated on the ground to produce imagery with a 50 kilometer swath width and a surface resolution of approximately 40 meters. The SIR is presently being upgraded into a new configuration termed SIR-B, in which the radar's antenna can be mechanically rotated in the Shuttle's payload bay during an orbital mission. SIR-B is currently scheduled for flight on the seventeenth Shuttle mission (STS-17) that is tentatively planned for August 1984. In its new configuration, the SIR-B can be used to image selected regions at different angles of incidence ranging from 15 deg to 60 deg (as measured from the local vertical). In principle, multiple incidence angle radar imagery of selected areas can be coregistered and used to differentiate surficial materials on the basis of their roughness characteristics. This procedure is conceptually similar to the use of multispectral imagery acquired at shorter wavelengths to discriminate surficial materials on the basis of their pigmentation.