Unified Full Wave Approach Research Articles

The scattering and depolarization of electromagnetic waves by random rough surfaces with different scales of roughness: New full wave solutions

A new unified full-wave approach is used to determine the like and cross polarized cross sections of composite random rough surfaces with significantly different scales of roughness. Traditionally, the solutions for such composite rough surfaces are expressed as sums of solutions based on the perturbation and the physical optics approaches. The full-wave solutions account for both specular point scattering and Bragg scattering in a unified, self-consistent manner. With the new unified full-wave approach, the incoherent radar cross sections are obtained by regarding the composite (multiple scale) rough surface as an ensemble of individual large scale scattering elements (patches) with arbitrary orientations. Thus the scatter cross sections, obtained from the original full-wave solution in a tilted co-ordinate system, are averaged over the large scale slopes (in and perpendicular to the plane of incidence) to obtain the cross sections of the composite surfaces. The rough surface height joint probability density function is assumed to be Gaussian.

A new unified full wave approach to evaluate the scatter cross sections of composite random rough surfaces

A new unified approach, based on the original full wave solutions, is presented to evaluate the like and cross polarized scattering cross sections of composite (multiple scale) random rough surfaces. The rough surfaces are assumed to be characterized by the Pieson-Moskowitz spectral density function. To account for the surface undulations, the incoherent radar cross sections are obtained by regarding the composite rough surface as an ensemble of pixels of arbitrary orientation.

Application of tilt modulation of the scatter cross-sections to distinguish between different non-Gaussian rough surfaces: unified full wave approach

Abstract The tilt modulations of the like- and cross-polarized cross-sections for arbitrarily oriented resolution cells are determined using the unified full-wave approach. A broad family of non-Gaussian rough surfaces characterized by the gamma surface height probability density functions of order K are considered. Furthermore a Pearson-Moskowitz surface height spectral density function is assumed for the sea surface. The surface height autocorrelation function is also assumed to be non-Gaussian. An arbitrarily oriented mean plane associated with the resolution cell is characterized by tilt angles in and perpendicular to a fixed reference plane of incidence. The ‘tilt modulation’ of the scattering cross-sections is determined as functions of the wavelength of the incident field 𝛌0 and the backscatter angle 0i 0. Each resolution cell represents the real (or synthetic) radar footprint. The size of the resolution cell, orientation, and the statistical characteristics of the non-Gaussian surface determine th...

Simulation of high resolution radar potarimetric images— unified full wave approach

Abstract The unified full wave approach is used to generate polarimctric images of composite rough surfaces illuminated by high resolution radar (i.e., real or synthetic aperture radars with small effective footprints). The unified full wave solutions account for Bragg scattering and specular point scattering in a self-consistent manner, therefore it is not necessary to decompose the surface into two surfaces with large and small roughness scales. The like and cross-potarized scattering cross-sections for the rough sea surface are tilt modulated due to the presence of swell or ship wakes. Hydrodynamic effects such as velocity bunching arc not considered here. The normal to an arbitrarily oriented mean plane associated with the illuminated resolution cell (pixel) is characterized by the tilt angles Q and t, in and perpendicular to, a fixed reference plane of incidence associated with the radar. The like and cross polarized backscatter cross sections of a tilted resolution cell are expressed in terms of the...

Tilt modulation of high resolution radar backscatter cross sections: unified full wave approach

The unified full wave approach is used to determine the tilt modulation of the like- and cross-polarized (high-resolution) radar backscatter cross sections for the rough sea surface. Real or synthetic aperture radars (SARs) with small effective footprints (resolution cells) are considered. Since the unified full-wave approach accounts for Bragg scattering as well as specular point scattering in a self-consistent manner, it is not necessary to adopt a two-scale model for the rough sea surface. The sea surface slope probability density function is assumed to be Gaussian. The backscattering cross sections are evaluated for all angles of incidence (normal to grazing). For tilts in the plane of incidence, the modulation of all the cross sections is largest at angles of incidence of 10 degrees . The cross-section modulation due to tilts perpendicular to the plane of incidence critically depends on the incident and scattered polarizations. The effective filtering of the large-scale spectral components of the rough sea surface by the high-resolution radar is accounted for, and the dependence of the cross-section tilt modulation on the size of the effective footprint is determined.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Scattering cross sections for non-Gaussian rough surfaces: unified full wave approach

The unified wave approach is used to compute both the like- and the cross-polarized scattering cross sections for composite rough surfaces characterized by a family of gamma functions of order K ranging from K=1 to K=25. This family of joint height probability density functions properly decorrelates to the product of the marginals as the surface height autocorrelation function vanishes. These results are compared with the like and cross-polarized cross sections for the surface with Gaussian characteristics (K to infinity ). It is shown how radar could be used most effectively to remotely sense the rough surface statistics of non-Gaussian rough surfaces. >

Acoustic backscatter cross sections for rough sea surface excited from above and below the air–water interface

Acoustic backscatter cross sections (normalized scattered pressure intensities) are evaluated for rough seas using a unified full-wave approach that accounts for specular point scatter and Bragg scatter in a self-consistent manner. Thus the two-scale model of the sea surface is not used in these investigations. Different surface wind speeds are considered. The full-wave cross sections are shown to be significantly different for excitations from above or below the air–water interface. The full-wave solutions are compared with the corresponding physical-acoustic and small-perturbation solutions.

Scattering cross sections for composite rough surfaces using the unified full wave approach

The full wave approach is used to derive a unified formulation for the like and cross polarized scattering cross sections of composite rough surfaces for all angles of incidence. Earlier solutions for electromagnetic scattering by composite random rough surfaces are based on two-scale models of the rough surface. Thus, on applying a hybrid approach physical optics theory is used to account for specular scattering associated with a filtered surface (consisting of the large sonic spectral components of the surface) while perturbation theory is used to account for Bragg scattering associated with the surface consisting of the small scale spectral components. Since the full wave approach accounts for both specular point scattering and Bragg scattering in a self-consistent manner, the two-scale model of the rough surface is not adopted in this work. These unified full wave solutions are compared with the earlier solutions and the simplifying assumptions that are common to all the earlier solutions are examined. It is shown that while the full wave solutions for the like polarized scattering cross sections based on the two-scale model are in reasonably good agreement with the unified full wave solutions, the two solutions for the cross polarized cross sections differ very significantly.