The Scanning L-band Active Passive (SLAP) instrument includes both a radiometer (passive microwave) and radar, operating with the same frequencies, polarizations, and conical scan geometry similar to that of the SMAP (Soil Moisture Active Passive) space mission. The SLAP radiometer operates at 1.4 GHz and features the same fully polarimetric observations with similar radio frequency interference (RFI) detection and mitigation capabilities as the SMAP radiometer. The beam width of the radiometer is 19° in the range direction and 12° in the azimuth direction yielding an oval footprint on the ground. Footprint size is also a function of aircraft altitude; during SLAPEX F/T, radiometer footprint size was approximately 250×500m for the linear transect flights and 400×800m to obtain complete spatial coverage of the SMAP grid cell.

Calibration

Radiometer calibration utilizes a combination of cold sky views before and after the campaign, ambient “warm” blackbody views before and after each flight, and in-flight internal calibration sources using open water over and lakes during each flight.

Sky Calibration

Box Calibration (Pre- or Post-Flight Calibration)

Water Calibration