Exploration of the Sea Surface Wind Speed Retrieval from the Geosynchronous Synthetic Aperture Radar

At present, the spaceborne synthetic aperture radars (SARs) are all carried on low earth orbit (LEO) satellites. Therefore, the coverage area of LEO SARs is small and the revisit period is long. In order to overcome the LEO SAR's shortcomings, the concept of the geosynchronous synthetic aperture radar (GEO SAR) comes into being. Compared with the LEO SAR, the GEO SAR can achieve a higher temporal resolution and thus can conduct frequent observations over a large area for a long time due to the high orbit (similar to 36000 km). The above advantages make the GEO SAR has a great benefit to monitoring the natural disasters and marine environment. The sea surface wind speed is one of the basic elements of the marine dynamic environment and can be retrieved from the LEO SAR imagery. Therefore, it is necessary to explore the potential of the GEO SAR in the sea surface wind speed retrieval. Since there is no GEO SAR on orbit so far, our study is based on the simulated GEO SAR images. By comparing with the input sea surface wind speeds in the simulation, we found that the C-band model function for equivalent neutral wind (CMOD5.N) still work for the simulated GEO SAR images. However, there is a certain difference between the input wind speeds and the retrieved wind speeds by CMOD5.N when the incidence angle is too large or small. Although it may be caused by the accuracy of the simulation, we fine-tuned the parameters in CMOD5.N by the least square method with the simulated GEO SAR images and the corresponding input wind speeds instead, as there are no real GEO SAR images till now. The evaluations of the sea surface wind speeds retrieved by the GEO SAR CMOD5.N were presented in the end.