The HYDROS RadiometerIRadar Instrument

A b s ~ The science objectives o f the HYDROS mission are to provide frequent, global measurements o f snrface soil moisture and surface f r d t h a w state. In order to adequately measure these geophysical quantities, the key instrument requirements were determined by the HYDROS science team to be: 1) Dualp o l a h t i o n L B a n d passive radiometer measurements at 40 km resolution, 2) Dual-polarization L-Band active rada r measurements at 3 km rrsolution, and 3) A wide swath to insure global three day refresh time for these measurements (1000 k m swath at the selected orbit altitude o f 670 km). As a solution to this challenging set o f instrument requirements, a relatively iargc, 6 meter, wnically-sunning reflector antenna architectore was selected fo r the instrument design. The deployable mesh antenna is shared by both the radiometer and radar electronics by employing a single L-Band feed.