Abstract: Offshore Wind Farm Inner-wake Investigation Using Dual-Polarized SAR Data

The analysis of inner park wakes in offshore wind parks is important to understand shadowing effects inside individual wind farms as well as the formation processes for external wakes, which are relevant for larger-scale power yield assessments and environmental impact studies. Synthetic Aperture Radar (SAR) systems have proven to be valuable tools for offshore wind energy resource assessment due to their capability to map ocean surface features with meter-scale resolution. Most SAR-related studies have primarily focused on large-scale atmospheric phenomena, particularly the characterization of far-field atmospheric wakes generated by wind farms. However, the potential of SAR for investigating inner-wake structures and wake dynamics within wind farms remains largely unexplored. This limitation is primarily attributed to signal contamination from turbine structures and reduced spatial resolution in wind speed retrievals, which is often implemented to suppress speckle noise. In this study, we propose a new methodology that combines vertical and cross polarisations (VV and VH) of the radar cross-section to address these challenges and improve the accuracy of inner-wake characterisation. The use of the cross polarisation VH helps enhance the reliability of the derived wind fields from the vertical polarisation VV. Application of this method to Sentinel-1 SAR data over the Amrumbank West and Kaskasi wind farms in the German Bight demonstrates that high-resolution SAR-derived wind fields can provide valuable insights into inner-wake behavior. This method preserves the high resolution and the visibility of the wake structure. Also, distinct differences in wake features between the two wind farms are identified and analysed.