Significant Wave Height Retrieved From Coherent X-Band Radar: A Physics-Based Approach

Significant wave height retrieval from X-band marine radars operating at grazing incidence is typically achieved by empirical algorithms that require extensive calibrations, which ideally are performed for every individual setup. Within this novel physics based approach coherent X-band marine radar data are being utilized to retrieve significant wave heights. In contrast to previously published methods, where the antenna had to be pointed into the main wave direction, this approach is utilized with a continuously rotating antenna. Radial velocities of surface scatterers are retrieved from the coherent radar data and converted under consideration of linear wave theory to surface elevations, which in turn are utilized to retrieve the significant wave height. The method was tested and applied to an extensive data set collected over a period of 29.5 days, covering four storms, at the offshore research platform Forschungsplattform in Nord und Ostsee 3 (FINO-3) in the southern North Sea. Comparison of radar retrieved significant wave heights to data obtained by a wave buoy in vicinity of FINO-3 resulted in a correlation of 0.99, a root mean square error of 0.31 m, and a bias of 0.09 m. In addition, sensitivity studies were carried out with respect to the quality of the signal, width of the dispersion filter and amount of data considered for calculations, to study the robustness of the method.