Wave and wind field extraction from ERS SAR imagery

This paper deals with the analysis of SAR imagery of the Mediterranean Sea to estimate the directional wave spectrum and the wind vector. As case study an ERS-2 SAR acquired on 13 November 1997 (orbit 13417, frame 2889) which includes Lampedusa Island in the Sicily Channel was selected. Lampedusa was chosen as test site because of its privileged location in the centre of the Mediterranean and because it hosts a fully equipped meteorological station. Besides, the selected SAR image shows a striking feature from which the wind direction can be reliably estimated. Wave field and wind vector from SAR image were compared with predictions from the WAM wave model and the wind output of the ECMWF atmospheric model, respectively. The retrieval of directional two-dimensional wave spectrum from SAR image was carried out by means of the classical Hasselmann & Hasselmann inversion scheme and the SAR image cross-spectrum methodology, respectively. Assuming the wind direction is known independently, SAR data was then analysed to retrieve the wind speed by using the predictions from empirical backscatter models, such as CMOD4 and CMOD-IFREMER. Wind vector retrieval results were validated against in situ measurements provided by the Lampedusa airport anemometer.