SMAP carries a radar and a radiometer that together will make measurements of soil moisture and freeze/thaw state of all non-liquid water surfaces on Earth. The radar and radiometer share a single feedhorn and reflector. The deployable mesh reflector is offset from nadir and rotates about the nadir axis at 14.6 rpm, providing a conically scanning antenna beam with a surface incidence angle of 40°. The 6 m (20 foot) antenna is made of gold-coated mesh. The gold-colored feedhorn sends out radar pings and receives radar returns. It also collects microwave emission from the same points Earth’s surface for the radiometer.
NASA/JPL
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