Passive Active L/S-band microwave aircraft sensor for ocean salinity measurements

A Passive/Active L/S-band (PALS) microwave aircraft instrument to measure ocean salinity has been built and tested. Because the L-band brightness temperatures associated with salinity changes are expected to be small, it was necessary to build a very sensitive and stable system. This new instrument has dual-frequency, dual polarization radiometer and radar sensors. The antenna is a high beam efficiency conical horn. The PALS instrument was installed on the NCAR C-130 aircraft and salinity measurement missions were flown on July 17-19, 1999, southeast of Norfolk, Virginia over the Gulf Stream. The measurements indicated a clear and repeatable salinity signal during these three days, which was in good agreement with the R/V Cape Hatteras 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 corresponded to the salinity increase of 0.4 psu measured by the M/V Oleander vessel.