Investigation of EM Backscattering from Slick-Free and Slick-Covered Sea Surfaces Using the SSA-2 and SAR Images

Honglei Zheng,Yunhua Wang,Helmi Ghanmi,Chaofang Zhao,Yanmin Zhang,Ali Khenchaf

doi:10.3390/rs10121931

Abstract

This paper is devoted to investigating the electromagnetic (EM) backscattering from slick-free and slick-covered sea surfaces at various bands (L-band, C-band, X-band, and Ku-band) by using the second-order small slope approximation (SSA-2) and the measured synthetic aperture radar (SAR) data. It is known that the impact of slick on sea surface is mainly caused by two factors: the Marangoni damping effect and the reduction of friction velocity. In this work, the influences induced by these two factors on the sea curvature spectrum, the root mean square (RMS) height, the RMS slope, and the autocorrelation function of sea surfaces are studied in detail. Then, the slick-free and slick-covered sea surface profiles are simulated using the Elfouhaily spectrum and the Monte-Carlo model. The SSA-2 with the tapered incident wave is employed to simulate the normalized radar cross-sections (NRCSs) of sea surfaces. Furthermore, for slick-free sea surfaces, the NRCSs simulated with the SSA-2 at various bands are compared with those obtained by the first-order small slope approximation (SSA-1), the classic two-scale model (TSM), and the geophysical model functions (GMFs) at various bands, respectively. For slick-covered sea surfaces, the SSA-2-simulated NRCSs are compared with those obtained from C-band Radarsat-2 images and L-band uninhabited aerial vehicle synthetic aperture radar (UAVSAR) images, respectively. The numerical simulations illustrate that the SSA-2 can be used to study the EM backscattering from slick-free and slick-covered sea surfaces, and it has more advantages than the SSA-1 and the TSM. The works presented in this paper are helpful for understanding the EM scattering from the sea surface covered with slick, in theory.

Highlights

Oil spill pollution on the sea surface is harmful to marine ecosystems, fisheries, wildlife, and other societal interests
It has been proven that synthetic aperture radar (SAR) is a useful tool for ocean remote sensing, especially for oil spill detection and monitoring
The motivation of this work is to investigate the influences caused by slicks on sea surface characteristics and the EM scattering from slick-covered and slick-free sea surfaces, both theoretically as well as experimentally

Summary

Introduction

Oil spill pollution on the sea surface is harmful to marine ecosystems, fisheries, wildlife, and other societal interests. The influences caused by slicks can mainly be described by two effects: the damping of small-scale sea waves, and the reduction of friction velocity. As a slick-covered surface is smoother, the friction velocity is reduced, and the energy transferred from the wind to sea waves is reduced.

Results

Conclusion