## 3 Results
### Effect of Non-Gaussianity on NRCS Simulation  
Previous studies focused on the scattering of a Gaussian sea surface. However, the natural sea surface is non-Gaussian, which means that it is necessary to consider the influence of non-Gaussianity on the prediction of the mean scattering and the scattering distribution. In this section, we evaluate the effect of the non-Gaussianity on the prediction of the sea surface distribution, average scattering, upwind-downwind asymmetry of backscatter, and scattering distribution at the incidence angles of 30\({}^{\circ}\)-50\({}^{\circ}\) and the wind speed range of 3-16 m/s, with the wind direction range of 0\({}^{\circ}\)-360\({}^{\circ}\) under VV and HH polarizations. The influence of non-Gaussian properties on scattering is introduced from two aspects. The first is the introduction of a non-Gaussian large-scale sea surface using the Tayfun model. The second is the introduction of the long-wave hydrodynamic modulation on the shortwave spectrum, which can be described using the modified TSM by adding a correction term associated with the bispectrum function into the conventional TSM. Figure 7 shows the comparison of the Gaussian and Tayfun sea surfaces at the wind speed of 10 m/s and incidence angle of 32\({}^{\circ}\) in the upwind direction. Figure 7a shows that the distribution of the Tayfun sea surface elevation deviates from that of the Gaussian surface owing to nonlinear effects, and the mean value shifts to a negative value. Figure 7b shows that the Tayfun sea surface has sharper crests and flatter troughs in comparison with the Gaussian sea surface. Moreover, Figure 7c shows that the non-Gaussian sea surface has higher probability near small slopes in comparison with the Gaussian surface, and there is no significant difference between the pdfs of the Gaussian and non-Gaussian sea surface slopes near the large slopes in the linear scale. All these results are similar to the performance of the CWM reported in [45]. The repeated experiment at high wind speed (i.e., 15 m/s) shows that the Tayfun ocean surface has the obvious characteristics of sharp peaks and flat troughs with a slight horizontal offset. The simulated average NRCSs based on the conventional TSM + Gaussian sea surface, conventional TSM + Tayfun sea surface, and modified TSM + Tayfun sea surface and their comparison with the reference data at the wind speed of 10 m/s as functions of the incidence angle in the upwind direction under VV and HH polarizations are shown in Figure 8a,b, and those in the downwind direction under VV and HH polarizations are shown in Figure 8c,d. The simulated average NRCSs and their comparison with the reference data at the incidence angle of 32\({}^{\circ}\) as a function of wind speed in the upwind direction under VV and HH polarizations are shown in Figure 9a,b, and those in the downwind direction under VV and HH polarizations are shown in Figure 9c,d. Figures 8 and 9 show that there is little difference between the mean NRCSs from the Gaussian and Tayfun sea surfaces based on the conventional TSM, which indicates that the introduction of non-Gaussian large-scale waves based on the Tayfun model has little effect on the prediction of the mean NRCS. In comparison, the simulated scattering based on the modified TSM is larger in the upwind direction and smaller in the downwind direction than the NRCS calculated using the conventional TSM owing to the introduction of bispectrum correction in the modified model. Moreover, the level of the correction introduced by the modified model changes little with an increase in wind speed for a given incidence angle, and it changes little with incidence angle for a certain wind speed. The absolute value of the bispectrum correction in the upwind direction is slightly larger than that in the downwind direction at a certain incidence angle and wind speed.