Experimental Study on the Properties of Microwave Echoes Backscattered From Breaking Waves

The assessment of the microwave backscattering characteristics from breaking waves is crucial for ocean remote sensing and ocean target recognition. Nevertheless, due to the tough experimental environment and the complex geometric profile of breaking waves, research on the microwave scattering characteristics of breaking waves is still preliminary. In this study, the echoes from breaking waves near shore were measured by a C-band radar, which was conducted at incident angles from 20° to 60° with both horizontal polarization (HH-Pol) and vertical polarization (VV-Pol), to reveal the properties of the normalized radar cross Section (NRCS) and the Doppler spectrum associated with wave breaking. The results show that the radar NRCS increases obviously when water waves are breaking. And, the HH–VV polarization ratio of the scattering field from breaking waves is close to 1. On the other hand, the frequency shift and the bandwidth of the Doppler spectrum of the scattered fields from breaking waves are both increasing. And, the Doppler spectrum may have multiple spectral peaks due to the stronger scattering intensity and higher velocity of the breaking waves. In this work, an empirical model for the NRCS backscattered from breaking waves is proposed within the incidence angle range from 20° to 60° along different observation directions. The experimental results can provide a reference for the subsequent research on microwave scattering characteristics of breaking waves.