The Shuttle Imaging Radar (SIR)-C instrument has been designed to obtain simultaneous multifrequency and simultaneous multipolarization radar images from a low Earth orbit. It is a multiparameter imaging radar that will be flown during two different seasons. The instrument has been designed to operate in innovative modes such as the squint mode, the extended aperture mode, and the scansar mode, and to demonstrate innovative engineering techniques such as beam nulling for echo tracking, pulse repetition frequency-hopping for Doppler centroid tracking, frequency step chirp generating, for polarization differentiation, and block floating-point quantizing for data compression. The instrument has also been designed to allow flexibility in selection of radar parameters such as pulsewidth and beamwidth in the tradeoff of image quality parameters. These SIR-C capabilities are to be directly transferred to the proposed Earth Observing System (Eos) synthetic aperture radar. >