Normalized roughness length estimation using derived sea state parameters from SAR

Studying air-sea interaction is essential for various coastal applications and structures, including offshore wind energy. The impact of waves on the atmospheric models is often described by introducing of the aerodynamic roughness length (z0) parameter, which is derived from various wave-related parameters. The global coverage and free-accessibility of Synthetic Aperture Radar (SAR) have the potential to enhance the coupling of atmosphere and wave using Sentinel 1-interferometric wide mode (S1-IW) in areas up to a few kilometers from coasts. This study introduces a method to overcome the so-called cutoff effect by imaging of sea state shorter than approximately 120 m using S1-IW. The validation of derived wave parameters from S1-IW against reference measurements was performed to assess the reliability of SAR images in wave related applications. The root- mean square error (RMSE) of derived significant wave height (H_s) and second moment wave period (T_m2) using the CWAVE_EX algorithm were 0.43 m and 0.8 sec, respectively. Significant reductions in H_s and peak wavelengths (Lp) were observed in shallow water depths. The z₀ was estimated using the well-known roughness scheme "Taylor and Yelland" and normalized for several positions in the study area. Significant differences in z₀ between shallow and deep waters for offshore winds (winds coming from land). Most buoys located at water depths and distances to the coastline less than 50 m and 50 km, respectively exhibited high values of z₀.