Statistical Comparison of Ocean Wave Directional Spectra Derived From SWIM/CFOSAT Satellite Observations and From Buoy Observations

The comparison and verification of ocean wave spectrum by remote sensing and in situ measurements at the spectral level are quite rare because the use of the traditional comparison method leads to very limited spatiotemporal matching pairs. In this article, a new comparison method is proposed. With this method, under different sea conditions (wind wave mainly/swell mainly) and sea surface conditions (wind speed smaller than 20 m/s and significant wave height from 1 to 7 m), mean directional wave height spectra from surface waves investigation and monitoring (SWIM) are compared at the spectral level to the buoy counterparts, in different classes of the sea state. This includes the comparison of the omnidirectional wave height spectrum and the directional function at the peak wavenumber. The comparison results show that, under medium and high sea conditions, wave directional spectra provided by the SWIM beams at 8 degrees and 10 degrees incidence have a high consistency with those from buoy data. Under low sea conditions, the measurement bias of SWIM wave directional spectra mainly comes from three phenomena that are, by order of importance, an abnormal lifting of spectral energy caused by nonwave components at low wave numbers (parasitic peak), from the nonlinear surfboard effect in the radar imaging mechanism, and from a slight underestimation of speckle noise spectral density.