DC-3
Douglas DC-3

The Passive Active L- and S-band Sensor (PALS) is a combined airborne polarimetric radiometer and radar developed by NASA’s Jet Propulsion Laboratory (JPL). It was designed to evaluate the advantages of merging passive and active remote sensors for measuring ocean salinity and soil moisture. Both the radiometer and radar in PALS operate across the L-band (1.41 GHz, 1.26 GHz) and S-band (2.69 GHz, 3.15 GHz) frequencies to measure brightness temperature and radar backscatter related to ocean salinity and soil moisture. Depending on the aircraft's altitude, PALS has a spatial resolution ranging from 600 to 1500 meters. Its design allows for installation on various aircraft and is typically used to validate observations from the Aquarius and SMAP satellite observations.