Polarimetric radiometer and scatterometer measurements of hurricane ocean winds

In September 1997, aircraft measurements of hurricane ocean surface winds were made over hurricane ERIKA which was located east of Bermuda. The microwave instruments included three polarimetric radiometers at 17, 19 and 37 GHz and a 14 GHz scatterometer. These instruments were mounted on the NASA P-3 aircraft and were flown around several locations near hurricane ERIKA to measure the azimuthal dependence of the polarimetric wind signal versus incidence angle. Estimates of the wind speed and direction were obtained using dropsondes dropped from the aircraft. Measurements of all 4 Stokes parameters of the ocean signal were made. In an area where there were high winds of 35 m/s and scattered clouds, there was a clear azimuthal signal in all the radiometric Stokes parameters, and in the scatterometer signal. Each of these signals was correlated with the wind direction. The radiometric wind signal was similar in all frequencies; however, there was significant variation with the incidence angle. At the larger incidence angles of 55 and 65 degrees, the fourth Stokes parameter, “V” had a peak to peak amplitude of ~1 K