Passive active L- and S-band (PALS) microwave sensor for ocean salinity and soil moisture measurements

A passive/active L/S-band (PALS) microwave aircraft instrument to measure o cean salinity and soil moisture has been built and tested. Because the L-ba nd brightness temperatures associated with salinity changes are expected to be small, it was necessary to build a very sensitive and stable system. Th is new instrument has dual-frequency, dual polarization radiometer and rada r sensors. The antenna is a high beam efficiency conical horn. The PALS ins trument was installed on the NCAR C-130 aircraft and soil moisture measurem ents were made in support of the Southern Great Plains 1999 experiment in O klahoma from July 8-14, 1999, Data taken before and after a rainstorm showe d significant changes in the brightness temperatures, polarization ratios a nd radar backscatter, as a function of soil moisture. Salinity measurement missions were flown on July 17-19, 1999, southeast of Norfolk, VA, over the Gulf Stream. The measurements indicated a clear and repeatable salinity si gnal during these three days, which was in good agreement with the Cape Hat teras ship salinity data. Data was also taken in the open ocean and a small decrease of 0.2 K was measured in the brightness temperature, which corres ponded to the salinity increase of 0.4 psu measured by the MN Oleander vess el.