The integral equation method for electromagnetic scattering from the ocean: Beyond a perfect conductor model

Abstract

Abstract. A version of the integral equation method is developed, which applies to scattering from a surface of a substance with a large dielectric constant e. An "impedance" boundary condition for the tangential components of electric and magnetic fields on the scattering surface is used, and the integral equation for the tangential components of the total magnetic field on a surface is formulated. This equation is applied to the problem of electromagnetic scattering from a slightly rough surface. It is demonstrated that the commonly used perfect conductor approximation (PCA) (e = •) can adequately describe scattering in the case of extremely large e only. The greatest sensitivity in scattering occurs when the incident and/or scattered waves are vertically polarized. For such cases the PCA does not work until e > 10 4. In the particular case of scattering from the ocean (ll 65), the PCA fails to provide an adequate description of the phenomena for either horizontally or vertically polarized waves, for practically all incidence and scattering angles. IntroductionDuring the last three decades, significant effort has been made and progress achieved in the theory of electromagnetic scattering from the ocean, using the integral equation The second reason, which applies to vertically polarized waves only, is of a physical nature. As one can observe from Fresnel's formulae (see also our equation (21)), the perfect conductor approximation fails drastically in properly describing even the reflection phenomenon from a plane boundary for neargrazing incidence angles 0in , when cos 0in --< Iwl-1/2, This deficiency is apparent in scattering as well. When combined with the numerical reason described above, a perfect conductor approximation actually fails not just for near-grazing angles, but over a very broad range of incidence/scattering angles except in cases of extremely large e (e > 10 4 for vertical polarization and e > 10 3 for horizontal). In the case of ocean scattering the effect of finite e is very large for all incidence/scattering angles and polarizations, being in particular most dramatic for vertically polarized waves.The theory presented in this paper extends the integral equation method to cases of finite but large dielectric constant e. The corrections to the results obtained by this method are of the order of e -1, which are really small (several percent, for seawater).The structure of this paper is as follows. Section 2 begins with a review of electromagnetic field representation in terms of electric (Je) and magnetic (Jm)

Lessons learned from full-spectral modelling of signatures of an estuary front

“…When a finite conductivity is assumed, this is not true. For this case, from an extension of Nedlin et al's [7] results, it follows that when the radar transmits and receives signals with vertical polarization with an angle of incidence angle BjnC, the associated RCS O N E ON is given by When WB effects are included, all simulations predict a signature (-1 1 &) that is in good agreement with measurement. A similar trend, in which negligible signature is obtained without WB and good agreement is found when WB is included, occurs in comparable plots for cases (not shown) in which the radar transmits and receives signals with horizontal polarization, and for the HT model.…”

“…the RCS expression om that results from the perfect conductor Kirchoff Approximation (KA) model due to Holliday and Thompson [6], and 3.) the comparable RCS expression o, due to Nedlin et a1 [7], which extends the HollidayRhompson (HT) result to cases involving a finite (but large) dielectric constant appropriate for water. Because the HT model applies to a perfect conductor, in the U, om is independent of polarization.…”

Robust Semi-Deterministic Facet Model for Fast Estimation on Em Scattering From Ocean-Like Surface

“…Kirchhoff approximation (KA) [4] and Small perturbation method (SPM) [5], and many unified theories like the two scale model (TSM) [6], small-slope approximation (SSA) [7], improved Green's function method (IGFM) [8], extended boundary condition method (EBCM) [9] and integral equation method (IEM) [10], have been discussed with application to sea scatter modeling. Many of the methods mentioned above more or less meet the possible limitation on special rigorous valid conditions, Gaussian spectrum, monostatic radar, one dimensional surface or insurmountable computational complexity.…”