Assessment of SAR offshore wind fields in the Gulf of Lion

The Mediterranean Sea heavily relies on fossil fuels for its energy supply, but the shift toward green energy is imminent. Offshore wind farms represent a pivotal step in this transition. However, deploying these wind farms effectively requires an accurate assessment of the wind potential in offshore areas.

Unlike Northern Europe, research on Mediterranean wind energy is sparse due to its intricate topography and bathymetry. The Mediterranean's coastlines, hemmed in by mountain ranges, create unique wind climates, posing challenges for modeling offshore wind conditions. Additionally, existing in-situ observations are limited to specific points.

Sentinel-1 satellite Synthetic Aperture Radar (SAR) wind fields can resolve wind variability at sub-km scales. The strength of satellite wind fields lies in the observation of large spatial domains over broad temporal periods. Therefore, this technology holds promise for uncovering the wind resource potential.

This study focuses on the Gulf of Lion, located in the NW Mediterranean Sea and currently the Mediterranean's most promising area for floating wind turbine installation. Here, two dominant local winds—the Mistral and Tramontane—prevail. The Mistral, a northerly wind, forms between the Alps and the Massif Central, while the Tramontane, a northwesterly wind, sweeps through the Aude valley between the Massif Central and the Pyrénées.

SAR records images of the radar backscatter from the Earth’s surface, which is commonly known as the Normalized Radar Cross Section (NRCS). NRCS values can be used as inputs in a Geophysical Model Function (GMF), along with other radar parameters, to retrieve the SAR ocean wind fields. For the SAR wind speed retrieval, a necessary input is the wind direction, commonly provided by numerical models. This study utilizes SAR wind speed retrievals driven by three numerical model wind directions—GFS and ERA-5 with 27 km spatial resolution, and New European Wind Atlas - NEWA (WRF) with 3 km spatial resolution—over a year-long period. We first compare the three model wind directions against in situ measurements from two buoys located in the greater area of the Gulf of Lion, which are provided by the Copernicus Marin Service In Situ TAC data platform.

Then, we compare the in-situ wind speeds against the three SAR wind speeds and the three model wind speeds. Our objective is to determine which SAR-model data synergy best reflects true wind conditions in the area. This study also aims to highlight the benefits of involving satellite-derived wind fields for wind resource estimations in upcoming wind farm areas characterized by complex wind climates.

This work is supported by the ESAWAAI project, funded by the European Space Agency under the grant agreement 4000142170/23/DT.