Tropical Cyclone Winds Retrieved from Synthetic Aperture Radar


This paper describes algorithms used to retrieve high-resolution wind fields in tropical cyclone conditions from synthetic aperture radar (SAR) data acquired at C-band with either co-polarization or cross-polarization. Wind directions are estimated from the orientation of wind-induced streaks visible in SAR images using a simple tropical cyclone flow field. Wind speeds are retrieved from the normalized radar cross section taking into account imaging geometry and SAR-retrieved wind direction using a geophysical model function. The algorithms are validated by comparing outputs to a set of SAR images acquired under tropical cyclone conditions. The simulated wind fields are compared to co-located results from the QuikSCAT scatterometer as well as to wind speeds measured by the Stepped Frequency Microwave Radiometer (SFMR) during reconnaissance flights through individual storms. Comparison of QuikSCAT winds to SAR co-polarization data shows that winds can be retrieved with a root mean square error of 17.6° for wind directions and 4.6 m s–1 for wind speeds. Comparison of SAR wind speeds to SFMR data result in a root mean square error of 5.7 m s–1 for co-polarization data and 3.8 m s–1 for cross-polarization data. SAR cross-polarization data are significantly better suited for SAR wind retrieval under tropical cyclone conditions at wind speeds above approximately 20 m s–1.
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