Sigma-0 retrieval from SeaWinds on QuikSCAT

NASA has developed a new scatterometer, Sea Winds, which is scheduled to be launched on two missions, one in 1999 and the other in 2000. SeaWinds will measure the speed and direction of near-surface winds over the ocean. A fundamental part of the processing of Sea Winds data is the computation of sigma degrees which includes solving the radar equation(1) for every pulse sent and received by the scatterometer. However, for Sea Winds, this calculation is too computationally intensive to perform in real time. Instead, a method of tabularizing most of the calculation has been developed. This method includes corrections for attitude and orbit perturbations and accounts for the elevation of the local topography. It also includes a table which will be used to assist ground data processing in determining the locations of the measurements. Tests comparing the tabulated results with the actual numerical calculations have shown that using this table is accurate to within +/-0.1 dB and gives locations that are accurate to within 160 meters. We provide a description of this algorithm. The innovations developed as part of this algorithm may be of interest in processing data from other remote sensing systems.