Multi-frequency polarimetric microwave ocean wind direction retrievals

The Naval Research Laboratory (NRL) and the Jet Propulsion Laboratory (JPL) have conducted several aircraft campaigns from 1994-1996 using polarimetric microwave radiometers to measure the ocean surface wind direction. The first flights in 1994 used the JPL 19 and 37 GHz polarimetric radiometers, which measure the first three Stokes parameters (I, Q, U). In 1995, NRL added a 10.8 GHz polarimetric radiometer and a dual polarization 22 GHz radiometer. In 1996, NRL modified the 10.8 GHz radiometer to measure all four Stokes parameters simultaneously. The experiments collected data at a variety of incidence angles during circle flights over National Data Buoy Center (NDBC) buoys, which were used for in situ data. The NDBC buoys reported the wind speed and direction with accuracies of ±1 m/s and +10°. In 1995, the buoys used were limited to those reporting every 10 minutes; the 1994 data were collected at buoys reporting hourly. Because there were no buoys near Hurricane Juliette, dropsondes were used for the necessary ground truth. Lastly, four flights were flown in November, 1996, out of NASA/Wallops Flight Facility (WFF) on the NASA/WFF P-3. These polarimetric brightness temperatures, together with in situ buoy wind data, verified the presence of a strong wind direction signal