MEASUREMENT OF OCEANIC WIND VECTOR USING SATELLITE MICROWAVE RADIOMETERS

We investigate the possibility of retrieving both wind speed and direction from microwave radiometer measurements of the ocean. The data for this investigation are the Special Sensor Microwave/Imager (SSM/I) measurements collocated with buoy reports from the National Data Buoy Center (NDBC). A physically based algorithm is used to retrieve the wind speed. The rms difference between the SSM/I and buoy wind speed is 1.6 m/s for 3321 comparisons. We find that the SSM/I minus buoy wind speed difference is correlated with wind direction. This correlation is due to a wind direction signal in the brightness temperatures (T(B)). For moderate wind speeds, the v-pol upwind T(B) is about 2 K higher than the downwind T(B). For h-pol observations, the T(B) maximum occurs at crosswind rather than upwind and is approximately 3.5 K higher than the minimum at downwind. When this wind direction signal is removed, the rms difference between the SSM/I and buoy winds reduces to 1.3 m/s. The wind direction signal is used to make global, low-resolution maps of the monthly mean oceanic wind vector. Finally, we assess the wind direction sensing capability of a prospective two-look satellite radiometer. Preliminary computer simulations indicate a direction accuracy of 15-degrees.