On Modeling of Quad‐Polarization Radar Scattering From the Ocean Surface With Breaking Waves

Abstract

Accurate estimates of microwave radar returns based on theoretical electromagnetic scattering models are of great benefit to obtain insight into the microwave scattering mechanism at the ocean surface. In this study, quad‐polarized radar backscatters from the regular ocean surface (no breaking waves) are first simulated using a composite surface Bragg model and a second‐order small slope approximation model, using three different surface roughness spectral models. The copolarized and cross‐polarized radar backscatters, induced by breaking waves, are then quantitatively estimated using two recent empirical models, which are dependent on incidence angles, wind speeds, and wind directions. Model‐simulated total radar backscatters, from regular surface waves and breaking waves, are statistically compared with measurements from spaceborne C‐band quad‐polarization RADARSAT‐2 synthetic aperture radar and also calculations from copolarized and cross‐polarized geophysical model functions. Results show that simulations of quad‐polarization radar backscatter are significantly improved when the effects of breaking waves are incorporated, especially for HH and VH polarizations.

Modeling and SAR Imaging of the Sea Surface: a Review of the State-of-the-Art with Simulations

“…The analysis is then carried out by comparison, for each spectrum of SAR image (intensity values of superimposed sea-ship waves I s ), with the reference image (intensity values of ambient sea waves I w ) in terms of peak signal-to-noise (PSNR), signal-to-noise (SNR), mean-squared error (MSE), standard deviation (STD) and the Structural Similarity (SSIM) index [135]. Since for different spectra models the absolute NRCS values change (as confirmed in many studies [81]- [84]) and because we are interested in relative changes of intensity values, all images and reference images were normalized before calculating the PSNR, SNR, MSE, STD, and SSIM measures. The STD measure was calculated for the difference image, which was determined as ∆I = I s − I w (in Fig.…”

“…To the best of our knowledge, an analysis in this respect has not been performed before. There are limited studies where various spectra are compared, but then only in terms of ensuing absolute NRCS values [81]- [84]. By contrast we employ five well-known sea wave spectra including Pierson-Moskowitz [85], JONSWAP [86], Fung and Lee [87], Elfouhaily et al [88] and Romeiser et al [73], and compare the contribution of these spectra to ship wake visualization in SAR images.…”

Study on Non-Bragg Microwave Backscattering from Sea Surface Covered with and without Oil Film at Moderate Incidence Angles

“…However, the prediction is not in agreement with observations for horizontal transmit horizontal receive (HH) polarization [4][5][6][7]. Even the composite surface theory considering the large-wave tilting does not remove this discrepancy between the simulation and the observation at HH polarization [8,9]. The possible reason for this is that non-Bragg scattering induced by steep waves and wave breaking plays a significant role in this process [1,4].…”

“…This section aims at presenting a survey of some of the most common sea spectrum models in the application of microwave backscattering simulation. The performances based on these sea spectra in the simulation of microwave scattering have been reported in many literatures, e.g., [9,27,28]. However, the works mentioned above do not eliminate the impact of non-Bragg scattering.…”

“…The NRCSs of total scattering were extracted from the three white lines in Figure 6. The NRCSs of non-Bragg scattering were calculated using Equation (9). Then, the NRCSs of "pure" Bragg scattering could be obtained by calculating the NRCSs differences of the total scattering and non-Bragg scattering.…”