Scanning L-Band Active Passive

The Scanning L-band Active/Passive (SLAP) instrument is an airborne simulator of NASA’s Soil Moisture Active/Passive (SMAP) satellite. Therefore, SLAP’s primary application is sensing soil moisture and soil freeze/thaw state, but it can also sense the salinity of coastal water. With a copy of SMAP’s digital back end, SLAP is also a great tool for observing manmade radio frequency interference (RFI).

Like SMAP, SLAP was built with two main sensors:

1. a passive microwave radiometer, the main soil moisture, freeze/thaw, and coastal salinity sensor for both SLAP and SMAP, and
2. an active microwave radar—also sensitive to soil moisture and freeze/thaw, but more useful for mapping variations in soil or sea surface roughness and vegetation—factors that complicate the sensing of soil moisture, freeze/thaw, and sea salinity. SMAP’s radar stopped working shortly after launch, but SLAP’s radar works fine. Note SLAP’s radar is a scatterometer, not a SAR, so the footprint size is similar to the radiometer footprint size.