Effect of Wind Direction on ENVISAT ASAR Wind Speed Retrieval

This paper presents an evaluation of effects of wind directions (NCEP, MANAL, QuickSCAT and WRF) on the sea surface wind speed retrieval from 75 ENVISAT ASAR images with four C-band Geophysical model functions, CMOD4, CMOD_IFR2, CMOD5 and CMOD5N at two target areas, Hiratsuka and Shirahama. As results, the WRF wind direction retrieves sea surface wind speeds with higher accuracies of the other wind directions at Hiratsuka. On the other hand, at Shirahama, it is not found an advantage of the WRF wind direction. Thus, the WRF wind direction cannot always retrieve wind speed with a high accuracy. However, a wind speed error generated with the WRF wind direction is the smallest of those with the other wind directions, and the error is as small as the level of SAR original radiometric errors. Consequently, the WRF wind direction is the most suitable of the four wind directions on the SAR wind speed retrieval when other error factors of the SAR wind speed retrieval are eliminated.