Testing the Algorithm for Determining the Near-Water Wind Direction Field Using Satellite Radiopolarimetric Measurements

Abstract

The original MicRAWinD (Microwave Radiometric Algorithm for Wind Direction retrieval) algorithm planned for use in reconstructing the near-surface wind direction in the Convergence space experiment (SE) is presented. The possibility of determining the wind direction based on radiometric measurements in two swaths of the radiometer stems from the anisotropy of surface radiation, which is manifested most clearly in the third Stokes parameter. Combining the results of measurements at different frequencies with their reliability factored in, one can improve the accuracy of reconstructing the wind direction. A new algorithm for enhancing the reliability of measurements which takes the real errors in measuring brightness temperatures into account is proposed. The algorithm has been tested with real data provided by the WindSat radiometric system. The results are compared with the Remote Sensing Systems (RSS) reconstruction data. A surface region with different geophysical parameters (sea surface temperature, vapor content, wind speed and direction, and cloud water content) is chosen for this comparison. The reconstruction algorithm involves solving the direct problem of calculating the radio brightness temperatures at linear ±45° polarizations with subsequent calculations of the third Stokes parameter for 37, 18.7, and 10.7 GHz. The initial meteorological parameters for the direct problem are products provided by RSS. The sensitivity of radiometric instruments is taken into account in the simulation process. The solution of the inverse problem and the comparison results demonstrate that this algorithm retrieves the wind direction with fine qualitative agreement both from the results of radiometric observations at a single frequency and from multifrequency data.