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

2021 ◽  
Vol 13 (13) ◽  
pp. 2443
Author(s):  
Honglei Zheng ◽  
Jie Zhang ◽  
Ali Khenchaf ◽  
Xiao-Ming Li
Keyword(s):  
Cross Sections ◽  
Sea Surface ◽  
Scale Model ◽  
Bragg Scattering ◽  
Total Scattering ◽  
Microwave Scattering ◽  
Wind Speeds ◽  
Geophysical Model ◽  
Radar Echoes ◽  
Radar Cross Sections

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.

scholarly journals Efficient Numerical Full-Polarized Facet-Based Model for EM Scattering from Rough Sea Surface within a Wide Frequency Range

2019 ◽  
Vol 11 (1) ◽  
pp. 75 ◽  
Author(s):  
Jinxing Li ◽  
Min Zhang ◽  
Ye Zhao ◽  
Wangqiang Jiang
Keyword(s):  
Cross Sections ◽  
High Efficiency ◽  
Wide Frequency Range ◽  
Sea Surface ◽  
Doppler Spectrum ◽  
Frequency Range ◽  
Em Scattering ◽  
Wind Speeds ◽  
Novel Approach ◽  
Rough Sea Surface

A full-polarized facet based scattering model (FPFSM) for investigating the electromagnetic (EM) scattering by two-dimensional electrically large sea surfaces with high efficiency at high microwave bands is proposed. For this method, the scattering field over a large sea facet in a diffuse scattering region is numerically deduced according to the Bragg scattering mechanism. In regard to near specular directions, a novel approach is proposed to calculate the scattered field from a sea surface based on the second order small slope approximation (SSA-II), which saves computer memory considerably and is able to analyze the EM scattering by electrically large sea surfaces. The feasibility of this method in evaluating the radar returns from the sea surface is proved by comparing the normalized radar cross sections (NRCS) and the Doppler spectrum with the SSA-II. Then NRCS results in monostatic and bistatic configurations under different polarization states, scattering angles and wind speeds are analyzed as well as the Doppler spectrum at Ka-band. Numerical results show that the FPFSM is a reliable and efficient method to analyze the full-polarized scattering characteristics from electrically large sea surface within a wide frequency range.

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

2018 ◽  
Vol 10 (12) ◽  
pp. 1931 ◽  
Author(s):  
Honglei Zheng ◽  
Yanmin Zhang ◽  
Ali Khenchaf ◽  
Yunhua Wang ◽  
Helmi Ghanmi ◽  
...  
Keyword(s):  
Synthetic Aperture Radar ◽  
Cross Sections ◽  
Monte Carlo Model ◽  
Sea Surface ◽  
Synthetic Aperture ◽  
Scale Model ◽  
Two Factors ◽  
L Band ◽  
The Impact ◽  
Aperture Radar

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.

scholarly journals Ocean Wind Retrieval Models for RADARSAT Constellation Mission Compact Polarimetry SAR

2018 ◽  
Vol 10 (12) ◽  
pp. 1938 ◽  
Author(s):  
Tianqi Sun ◽  
Guosheng Zhang ◽  
William Perrie ◽  
Biao Zhang ◽  
Changlong Guan ◽  
...  
Keyword(s):  
Cross Sections ◽  
Quadratic Function ◽  
Retrieval Model ◽  
Retrieval Models ◽  
Wind Retrieval ◽  
Geophysical Model ◽  
Radar Cross Sections ◽  
Geophysical Model Function ◽  
Ocean Wind

We propose two new ocean wind retrieval models for right circular-vertical (RV) and right circular-horizontal (RH) polarizations respectively from the compact-polarimetry (CP) mode of the RADARSAT Constellation Mission (RCM), which is scheduled to be launched in 2019. For compact RV-polarization (right circular transmit and vertical receive), we build the wind retrieval model (denoted CoVe-Pol model) by employing the geophysical model function (GMF) framework and a sensitivity analysis. For compact RH polarization (right circular transmit and horizontal receive), we build the wind retrieval model (denoted the CoHo-Pol model) by using a quadratic function to describe the relationship between wind speed and RH-polarized normalized radar cross-sections (NRCSs) along with radar incidence angles. The parameters of the two retrieval models are derived from a database including wind vectors measured by in situ National Data Buoy Center (NDBC) buoys and simulated RV- and RH-polarized NRCSs and incidence angles. The RV- and RH-polarized NRCSs are generated by a RCM simulator using C-band RADARSAT-2 quad-polarized synthetic aperture radar (SAR) images. Our results show that the two new RCM CP models, CoVe-Pol and CoHo-POL, can provide efficient methodologies for wind retrieval.

scholarly journals Towards the Sea Ice and Wind Measurement by a C-Band Scatterometer at Dual VV/HH Polarization: A Prospective Appraisal

2020 ◽  
Vol 12 (20) ◽  
pp. 3382
Author(s):  
Alexey Nekrasov ◽  
Alena Khachaturian ◽  
Ján Labun ◽  
Pavol Kurdel ◽  
Mikhail Bogachev
Keyword(s):  
Wind Speed ◽  
Sea Ice ◽  
Cross Sections ◽  
Potential Application ◽  
Geophysical Model ◽  
Radar Cross Sections ◽  
Statistical Distance ◽  
Sea Wind ◽  
Ice Water ◽  
Discrimination Method

Following the mission science plan of EPS/Metop-SG C-band scatterometer for 2023–2044, we consider the potential application of the sea ice/water discrimination method based on the minimum statistical distance of the measured normalized radar cross sections (NRCS) to the geophysical model functions (GMF) of the sea ice and water, respectively. The application of the method is considered for the classical spacecraft scatterometer geometry with three fixed fan-beam antennas and the hypothetical prospective scatterometer geometry with the five fixed fan-beam antennas. Joint vertical (VV) and horizontal (HH) transmit and receive polarization are considered for the spaceborne scatterometer geometries. We show explicitly that the hypothetical five fixed fan-beam antenna geometry combined with the dual VV and HH polarization for all antennas provides better estimates of the sea wind speed and direction as well as sea ice/water discrimination during single spacecraft pass. The sea ice/water discrimination algorithms developed for each scatterometer geometry and dual VV/HH polarization are presented. The obtained results can be used to optimize the design of new spaceborne scatterometers and will be beneficial to the forthcoming satellite missions.

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