SAR Offshore Wind Fields in the Gulf of Lion

Offshore wind energy is rapidly growing due to high wind speeds and low visual impact at sea. In the North-Western Mediterranean, the Gulf of Lion is one area where floating offshore wind turbines will be installed. A de-tailed analysis of synthetic aperture radar (SAR) scenes revealed wind flow patterns induced by coastal orography, such as flow channeling and horizontal lee waves, often unresolved in model wind fields, thus quantifying the local winds of the Tramontane and the Mistral. High-accuracy wind speeds retrieved at a 10-m level from satellite-borne SAR offer significant insight for wind resource estimation. Copolarized SAR wind speed retrievals depend on wind direction input. Our motivation is to investigate the importance of reliable wind direction input in the SAR wind retrieval based on 1 year of wind direction data from the Global Forecast System (GFS), fifth major global reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) (ERAS), and the New European Wind Atlas (NEWA). We validated these against buoy data to assess their accuracy. While ERAS showed the most accurate wind direction, this did not translate into high-precision SAR wind speeds. The three derived SAR wind speeds showed correlation coefficients of R² between 0.90 (0.81) and 0.94 (0.84) against the Lion (Begur) buoy datasets with the best agreement being with ERAS and NEWA at the Lion and Begur buoys, respectively. These results suggest no preferred numerical model wind direction input for SAR retrievalks.