CoAuthors

ping chen (tutor, China); Daniele Hauser (tutor, France); jianyang Si (senior, China)

The wave scatterometer is a real aperture radar with low incident angles. Its echoes from the sea surface are mainly quasi-specular scattering. While long waves will cause tilt modulation of the echo signal, the information of long waves can be inverted linearly from the modulation signal to obtain the wave spectrum. However, under some incident angles and sea surface conditions, the echo signal includes not only the tilt modulation from long waves but also the nonlinear modulation, that is, the hydrodynamic modulation and the surfboard effect. In this paper, we simulate with a Monto Carlo method the influence of the surfboard effect and hydrodynamic modulation effect on the performance of wave spectrum inversion by SWIM when they act alone or together. The simulation results show that if only the surfboard effect exists, when the incident angle is small and the wave steepness is large, the surfboard effect will cause the backscattering of different sea surface elements to accumulate to the same range gate, resulting in the inverted wave spectrum at the peak wavenumber being underestimated and left-shifting of the peak wavenumber. If only the hydrodynamic modulation effect exists, i. g., the roughness of short waves is related to the wave height, the roughness of short waves is larger at the wave crests and smaller at the troughs, the inverted wave spectrum to be overestimated, especially in the region around the peak wavenumber. If the two effects exist together, the effects of the surfboard effect and the hydrodynamic modulation are mutually offsetting and only when the influence of the surfboard effect is extremely small, the effect of the hydrodynamic modulation will be highlighted. The above simulation results on the nonlinear effect on the performance of the inverted wave spectrum, are validated by the comparison of the omnidirectional spectrum of buoy measurements and SWIM measurements under different sea states and sea surface conditions.