Cross-polarized Cross Sections Research Articles

Scattering From Inhomogeneous Dielectric Cylinders With Finite Length

The electromagnetic scattering by a dielectric cylinder of finite length is important in many applications, particularly for microwave remote sensing of vegetated terrain. Yet, not only a unified analytical solution is still elusive in providing the scattering cross sections but also other important aspects, such as the phase of the scattering amplitude function, energy conservation, and reciprocity relation, have been scantly touched in the literature. The treatment of a dielectric inhomogeneous cylinder of finite length brings forth new challenges. Taking on such challenges is the focus of this paper. The main plan of attack is to extend the virtual partition method, which is a T-matrix-based semi-analytical model, that we have previously proposed to treat scattering from a homogeneous dielectric cylinder of finite length, to the inhomogeneous cases. The effectiveness of the proposed method is validated numerically, including: 1) high-fidelity prediction of the copolarized and cross-polarized cross sections for arbitrary bistatic scattering configuration; 2) high-fidelity predictions of the phase of the scattering amplitude function; 3) verification of energy conservation; and 4) verification of the reciprocity theorem.

Double-scatter cross sections for two-dimensional random rough surfaces that exhibit backscatter enhancement.

Full-wave solutions are given for the single- and double-scatter radar cross sections for two-dimensional random rough surfaces. High-frequency approximations are used for the double-scatter cross sections in order to express them as numerically tractable four-dimensional integrals. The major contributions to the double-scatter cross sections are associated with the quasi-parallel and quasi-antiparallel double-scatter paths. They come from the neighborhoods of specular points. The enhancement of the backscatter cross sections, which is associated with the quasi-antiparallel double-scatter paths, is observed for both the like- and cross-polarized cross sections.

A numerical study of the composite surface model for ocean backscattering

A numerical study of 14-GHz backscattering from ocean-like surfaces, described by a Pierson-Moskowitz spectrum, is presented. Surfaces rough in one and two dimensions are investigated, with Monte Carlo simulations performed efficiently through the use of the canonical-grid expansion in an iterative method of moments. Backscattering cross sections are illustrated for perfectly conducting surfaces at angles from 0 to 60/spl deg/ from normal incidence, and the efficiency of the numerical model enables the composite surface theory to be studied in the microwave frequency range for realistic one-dimensional (1D) surface profiles at low wind speeds (3 m/s). Variations with surface spectrum low-frequency cutoff (ranging over spatial lengths from 21.9 to 4.29 cm) are investigated to obtain an assessment of composite surface model accuracy. The 1D surface results show an increase in hh backscatter returns as surface low-frequency content is increased for incidence angles larger than 30/spl deg/, while /spl nu//spl nu/ returns remain relatively constant, all as predicted by the composite surface model. Similar results are obtained for surfaces rough in two dimensions, although the increased computational complexity allows maximum surface sizes of only 1.37 m to be considered. In addition, cross-polarized cross sections are studied in the two-dimensional (2D) surface case and again found to increase as surface low-frequency content is increased. For both 1D and 2D surfaces, backscattering cross sections within 20/spl deg/ of normal incidence are found to be well matched by both Monte Carlo and analytical physical optics (PO) methods for all low-frequency cutoffs considered, and a comparison of analytical PO and geometrical optics (GO) results indicates an appropriate choice of the cutoff wavenumber in the composite surface model to insure an accurate slope variance for use in GO predictions. This choice of cutoff wavenumber is then applied in the composite surface theory for more realistic ocean spectra and compared with available experimental data.

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...

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. >