SMAP (Soil Moisture Active Passive)

SMAP, Soil Moisture Active Passive, is NASA’s L-band mission launched 31 January 2015 to map soil moisture and freeze-thaw state. It carried an L-band radar and an L-band radiometer near 1.4 GHz; the radar failed in July 2015, so the mission now runs on the radiometer alone. Over the ocean the same L-band brightness temperature retrieves sea surface salinity, and SMAP performs well in high winds where it also yields a hurricane wind speed product. L-band, near 21 cm wavelength, sees through vegetation and light rain and reaches a few centimeters into soil, the band that makes salinity and soil moisture measurable from orbit.