An FFT-Based Implementation of the First-Order Small-Slope Approximation for Simulating Microwave Scattering From Sea Surface

This article presents a simple and efficient implementation of the first-order small-slope approximation (SSA-1) to simulate the normalized radar scattering cross section (NRCS) from ocean surface based on fast Fourier transform (FFT) of the equivalent sea surface autocorrelation function. The implementation process only takes a pair of FFT operations between sea wave spectrum and sea surface autocorrelation function. Compared with the reported implementations of SSA-1 model based on the series expansion, the proposed method (called as "FFT-based implementation") reduces the computation amount of FFT operations greatly. To examine the accuracy and efficiency of the FFT-based implementation relative to the direct integration implementation of SSA-1 (called as "classical implementation"), the monostatic and bistatic NRCSs simulated by using the two implementations with the help of Elfouhaily sea spectrum at various radar frequencies and sea states are compared. The comparison results indicate the FFT-based implementation not only holds almost the same accuracy as the classical implementation but also has a higher efficiency, especially for the simulation scenarios with small Rayleigh parameters. Furthermore, we discuss the influence of sampling range and sampling interval of sea spectrum components on the accuracy and efficiency of the FFT-based implementation and its feasibility on the simplified second-order SSA (SSA-2) model with the mathematic expression similar to SSA-1. The simulation results show that the sampling range and sampling interval of sea spectrum have different effect on the accuracy and efficiency of the FFT-based implementation, and the proposed implementation method is also feasible for the simplified SSA-2 model.