Abstract
In the past decades, Bragg scattering has been considered to be an important scattering mechanism of microwave backscattering from sea surfaces. However, as reported in many recent literatures, non-Bragg scattering (which is often attributed to wave breaking) also makes a significant impact on radar scattering, especially for Horizontal–Horizontal (HH) polarized radar signals. To date, we know far less about non-Bragg scattering than Bragg scattering. Herein, this paper carries out an investigation on non-Bragg scattering and its effect on radar echoes at moderate incidence angles, both for oil-free and oil-covered sea surfaces. This paper firstly presents a systematic comparison of several sea spectra commonly used for the simulation of microwave scattering from sea surfaces. It is found that none of them perform well for the description of Bragg waves. Then, the “pure” Bragg wave spectra are inverted in the framework of the two-scale model (TSM) and geophysical model functions (GMFs). The normalized radar cross sections (NRCS) related to total scattering, non-Bragg scattering, and “pure” Bragg scattering in C, X, and Ku-bands are simulated under various conditions (i.e., incidence angles, wind speeds, and wind directions). Quantitative assessments of the relative contributions of non-Bragg scattering to total scattering are conducted. We also perform a survey on the non-Bragg scattering from the oil-covered sea surface. This article provides some new insights for a better understanding of the non-Bragg microwave scattering from rough sea surfaces at moderate incidence angles.
Highlights
Introduction published maps and institutional affilMicrowave radars play an increasingly important role in ocean observation thanks to their capability of providing valuable data under all-weather, all-day, and all-night conditions
The normalized radar cross section (NRCS) or scattering coefficient as a parameter to describe the scattering strength is highly sensitive to the ocean-surface roughness induced by gravity–capillary surface waves, which can be influenced by various factors, such as the strength of local wind, the surfactant floating on the sea surface, etc. [1]
9a,b,d,e,g,h, normalized radar cross sections (NRCS) of the non-Bragg scatterBragg scattering is different for different kinds of oil film, which is consistent with the ing is different for different kinds of oil film, which is consistent with the results presented results presented in
Summary
As expressed in Equation (3), to simulate the microwave Bragg scattering accurately, the primary task is to develop a spectral model accurate enough for modeling Bragg sea waves. Is simulated based on the TSM and various sea spectra, which eliminates the non-Bragg scattering component and is directly related to the Bragg wave spectrum [19,29]. 1b, the results simulated by using the E spectrum and H spectrum are better than those of other spectra for Ku-band. In. Figure 1b, the results simulated by using the E spectrum and H spectrum are better than those of other spectra for Ku-band. The results simulated by using E spec of 18 trum and H spectrum agree better with GMFs than the other spectra. For Ku-band, result of Ethat spectrum matches well differences amongst the TSM and. Amongst the TSM and GMFs under different conditions, whatever sea spectra are adopted
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