The Soil Moisture Active/Passive (SMAP) Mission Radar: A Novel Conically Scanning SAR

The Soil Moisture Active/Passive (SMAP) mission is a NASA mission identified by the NRC "decadal survey" to measure both soil moisture and freeze/thaw state from space. The mission will use both active radar and passive radiometer instruments at L-Band. In order to achieve a wide swath at sufficiently high resolution for both active and passive chan-nels, an instrument architecture that uses a large rotating reflector is employed. The active radar will further utilize SAR processing in order to obtain the sub-footprint resolution necessary for the geophysical retrievals. The SMAP radar has a unique geometry where the antenna footprint is continuously rotated about nadir in a conical fashion, as opposed to the more common side-looking SAR design. In additional to the unconventional scan geometry, the SMAP radar must address the effects of Faraday rotation and radio frequency interference (RFI), both consequences of the L-Band frequency of operation.