## 1 Introduction  
The theoretical investigation of microwave backscatter from the ocean surface is of great value for the geophysical interpretation of microwave remote-sensing retrievals of ocean surface winds, waves, and currents. In recent decades, research on the physical processes involved in electromagnetic-ocean-surface interactions has identified that the most important mechanism contributing to ocean backscatter at moderate incidence angles is resonant Bragg scattering. Many physical models have been developed to describe Bragg scattering, such as the small perturbation method [1], two-scale model (TSM) [2; 3], small-slope approximation [4], and integral equation method [5]. However, most related studies focused on the average backscatter from a large-scale sea surface on the order of tens of kilometers and ignored fluctuations corresponding to local spatiality characteristics. Such local information is valuable and desirable in the simulation of intensity patterns acquired by a synthetic aperture radar with a high resolution. Considering this demand, research has focused on facet-based methods that divide the ocean surface into facets and obtain the scattering contribution from each individual facet. For example, [PERSON] et al. [6; 7; 8] presented a facet backscatter model in which the Kirchhoff solution of the physical optics approximation was used to compute the facet scattering, and then a shortwave modification of the facet was used to revise the phase factor that accounts for the microstructure (ripples). [PERSON] et al. [9] used the small perturbation method to predict the scattering of a facet Gaussian sea surface that is isotropic. [PERSON] et al. [10] and [PERSON] et al. [11] built a more exact simulation of the scattering phase distribution and provided a modified TSM, called the capillary wave modification facet scattering model, to evaluate the scattering from facet non-Gaussian sea surfaces, either in the monostatic or the bistatic cases. In [12], [PERSON] et al. calculated the scattering of a nonlinear sea surface based on the capillary wave modification facet scattering model. In [13; 14], [PERSON] et al. combined the Kirchhoff approximation with the small perturbation method to obtain the bistatic normalized radar cross section (NRCS) of a Gaussian sea surface. Most previous studies of facet scattering were carried out based on the JONSWAP spectrum [15] and the Elfouhaily spectrum [16]. The JONSWAP spectrum, developed by [PERSON] et al. in 1973, is a gravity wave spectrum [15]. The Elfouhaily spectrum is a unified spectrum that combines the JONSWAP wave spectrum and the short-wave spectrum derived from wave tank data [17]. However, many wind wave spectra have been developed to date. Different spectra have different performances in NRCS prediction under various incidence angles and wind speeds. Therefore, it is necessary to analyze the influence of wind wave spectra on the prediction of facet scattering. The influence of the non-Gaussianity on facet scattering simulation also needs to be further discussed at different incidence angles, wind speeds, and wind directions. Additionally, the swell, which can not be ignored in the actual ocean environment, is a significant factor as well. Swell can change the height fluctuation and slope distribution of the sea surface, and thus it can cause changes in scattering patterns. However, most studies focused on the influence of swell on the mean NRCS prediction and ignored the impact of swell on the simulation of scattering distribution. So, it is necessary to discuss the effect of swell on facet scattering.