Arnaud Coatanhay

Bistatic scattering from an anisotropic sea surface: Numerical comparison between the first-order SSA and the TSM models

The first-order small-slope approximation (SSA-1) model is used for numerical predictions of the normalized radar cross section (NRCS) of an anisotropic ocean surface in bistatic configurations for the K u -band radar frequency. The calculations were made by assuming the Elfouhaily et al. surface-height spectrum for fully developed seas. In the forward–backward case, the SSA-1 presents an agreement with the geometric optics limit of the Kirchhoff approximation results in the near-specular directions where it is well known that the last model works well. In the fully bistatic case, SSA-1 numerical results are compared with those of the two-scale model in several configurations as a function of wind speed, wind direction, incident/scattering angles and for co-and cross-polarization states. Good agreement between the two models is noted in the co-and cross-polarization case with a small difference of about 1–2 dB. But in certain configurations, the SSA-1 model tends to overestimate the radar cross section peak behaviour. This irregularity is discussed and interpreted. The main purpose of this paper is to analyse NRCS predictions based on the SSA-1 model in a fully bistatic configuration.

An Improved Two-Scale Model for the Ocean Surface Bistatic Scattering

Remote sensing applications require developing accurate models to predict radar bistatic scattering from rough surfaces. In this context, an improved two-scale model (TSM) is proposed for electromagnetic bistatic scattering from sea surface. The simplest TSM combines the first order small perturbation method (SPM1) with Kirchhoff Approximation. We add the second order SPM contribution to SPM1 to develop an improved TSM. The calculations are made by assuming the surface-height spectrum of Elfouhaily et al. for fully developed seas. In backscattering configuration the numerical results are compared with the published experimental data and SSA. The new TSM results are in good agreement with the experimental data specially, in cross-polarization. Finally, we use the new TSM to predict the sea scattering in bistatic configuration and compare the results with SSA.

SCATTERING NEAR A PLANE INTERFACE USING A GENERALIZED METHOD OF IMAGES APPROACH

A new method for predicting the scattered acoustic field due to a plane wave incident upon an infinitely long cylinder lying near an penetrable plane interface is presented. The method generalizes the method of images which is restricted to rigid and soft plane interfaces. Validity domains, physical interpretations, simulations and numerical results are described for sedimentary medium-fluid plane interfaces. And, they are well compared with high frequency asymptotic results based on the Geometrical Theory of Diffraction(G.T.D.).

The influence of ripple damping on electromagnetic bistatic scattering by sea surface

Organic films and oil slicks modify the sea surface physics (permittivity, spectrum and slope distribution) depending on their viscosity, their bulk concentration and their diffusion coefficient. In this paper, special focus is given to the influence o f a pollutant upon the electromagnetic scattering by the sea surface . Our study is based on the sea spectrum variation described with a fluid mechanic model. More, the electromagnetic scattering is evaluated in various bistatic configurations using a Two-Scale Model (TSM).

Simulations of the bistatic scattering using two-scale model and the unified sea spectrum

This paper deals with the simulations of scattering by the sea surface using Two- Scale Model (TSM) and the realistic unified sea spectrum in various bistatic configurations. After a brief theoretical presentation, our numerical results (scattering matrix coefficients) are compared with measured data, with a semi-empirical model (CMOD5) and with other analytical models (Small Slope Approximation) in backscattering configuration. Then, we study the influence of sea parameters (wind speed and wind direction) upon the co- and cross-polarization signature in various bistatic configurations. Finally, we present the simulation of the signal received by an observer above the sea when a plane incident wave impinges on the ocean surface.

Comparison between small slope approximation and two scale model in bistatic configuration

The Small Slope Approximation (SSA) and Two Scale Model (TSM) are applied to the prediction of microwave sea scattering in bistatic configuration. The calculations were made by assuming the surface-height spectrum of Elfouhaily et al for fully developed seas. Both the coand cross-polarization cross section are calculated in several bistatic configuration. The simulations showed good agreement between SSA and TSM for Kuand C-bands. For the HH polarization, a significant difference between results obtained with two models is remarked specially near the grazing angles and for large wind speed. Numerical results are obtained as a function of wind speed, incident/scattering angles and polarization states.

Project MOPS marine opportunity passive systems

The main purpose of this paper is to present a new project of research called MOPS dedicated to the use of the GNSS signals for the oceanography and the sea surface monitoring.

Bistatic radar scattering from an ocean surface at L-band

This paper presents a numerical analysis for bistatic scattering from the sea surface at L-band. The unifying scattering model small slope approximation (SSA) of the first order is applied to calculate normalized bistatic cross section (NBCS) of the ocean surface. The calculations were made by assuming the surface-height spectrum of Elfouhaily et al. The correlation function based on this spectrum is calculated. The negative region participation in surface scattering which is function of the incident angle, the wind speed and the exploring wavelength is discussed. A comparison between SSA and geometric optics models shows that the last one is generally not accurate at L-band especially at large angles of incidences. Numerical results examine the wind dependency over a wide range of incident angles along the specular direction and in the forward scattering configuration. In addition, the NBCS behavior in fully bistatic configuration is predicted. Numerical results are obtained as a function of wind speed, incident/scattering angles and polarization states.

Frequency impact on the bistatic radar scattering from an ocean surface

In this paper we study the frequency impact on the normalized bistatic cross section (NBCS) of the sea surface. Numerical simulations are presented and analyzed in the frequency range from 1 to 14 GHz (L- to Ku-band). We treat this problem with the unifying scattering model denoted small slope approximation (SSA). The computations were made assuming the surface-height spectrum of Elfouhaily et al. for fully developed seas. Numerical results are obtained and discussed in both forward and fully bistatic configurations for different sea states and polarizations.

New concept of passive measure using GNSS reflected signals in oceanographic applications

Today, one of the methods in monitoring oceans is the use of radar systems or more generally the use of electromagnetic diffusion. Thanks to the deployment of satellite navigation systems (GNSS), such as GPS, GNSS signals are being used more and more as an opportunity source for this kind of observation. This paper assesses the measurement of oceanographic parameters within a few meters near the surface. The oceanographic phenomena that is currently available for recording is limited. That is why we propose a much finer analysis of the diffusion and the scattering of GNSS signals near ocean surface, by employing very fine time steps and integration over the long periods of code. The final goal is to be able to perceive very fine phenomena, among which the ocean surface kinematics. In order to achieve this, the application of sophisticated processing algorithms is needed. In this work we simulate and highlight the observable effects expected as a result of use of such a method. The work is realized as a part of the MOPS project.