The HYDROS radiometer/radar instrument

The science objectives of the Hydrosphere State Mission (HYDROS) are to provide frequent, global measurements of surface soil moisture and surface freeze/thaw state. In order to adequately measure these geophysical quantities, the key instrument requirements were determined by the HYDROS science team to be: (1) Dual-polarization L-Band radiometer measurements at 40 km resolution, (2) Dual-polarization L-Band radar measurements at 3 km resolution, and (3) A wide swath to insure global three-day refresh time for these measurements (1000 km swath at the selected orbit altitude of 670 km). As an optimal solution to this set of instrument requirements, a relatively large, 6-meter, conically-scanning reflector antenna architecture was selected for the instrument design. The deployable mesh antenna is shared by both the radiometer and radar instruments by using a single L-Band feed.