Physics-based Two-grid Method Research Articles

MICROWAVE EMISSION FROM TWO-DIMENSIONAL INHOMOGENEOUS DIELECTRIC ROUGH SURFACES BASED ON PHYSICS-BASED TWO-GRID METHOD

Numerical simulations of emission for two-dimensional randomly rough surfaces with an inhomogeneous layered medium are presented. The inhomogeneous layered medium is modeled by a generalized n-layered stratified media. The numerical method was adopted from the physics-based two-grid method (PBTG). To ensure the strict accuracy requirement while to relief the memory and CPU resources, the PBTG in conjunction with the sparse-matrix canonical grid method (SMCG) was used in this paper. In so doing the reflected terms of the dyadic Green's function that accounts for layered media were added into the integral equations governing the surface tangential fields. Since the reflected part of the dyadic Green's function does not

Bistatic scattering and transmitting through a fractal rough surface with high permittivity using the physics-based two-grid method in conjunction with the forward-backward method and spectrum acceleration algorithm

To numerically calculate bistatic scattering from a fractal rough surface with high permittivity, a comprehensive approach of the forward-backward method (FBM) with spectral acceleration algorithm (SAA) combined with the physics-based two-grid (PBTG) method is developed. Bistatic scattering from and transmitting through one-dimensional (1-D) fractal rough surface with high permittivity, under TE and TM tapered wave incidence, are numerically simulated. Angular reflectivity and transmittivity demonstrate the energy conservation and the functional dependences upon the surface parameters.

Application of physics-based two-grid method and sparse matrix canonical grid method for numerical simulations of emissivities of soils with rough surfaces at microwave frequencies

The simulations of emissivities from a two-dimensional (2D) wet soil with random rough surfaces are studied with numerical solutions of three-dimensional (3D) Maxwell equations. The wet soils have large permittivity. For media with large permittivities, the surface fields can have large spatial variations on the surface. Thus, a dense discretization of the surface is required to implement the method of moment (MoM) for the surface integral equations. Such a dense discretization is also required to ensure that the emissivity can be calculated to the required accuracy of 0.01 for passive remote sensing applications. It has been shown that the physics-based two-grid method (PBTG) can efficiently compute the accurate surface fields on the dense grid. In this paper, the numerical results are calculated by using the PBTG in conjunction with the sparse-matrix canonical grid method (SMCG). The emissivities are illustrated for random rough surfaces with Gaussian spectrum for different soil moisture conditions. The results are calculated for L- and C-bands using the same physical roughness parameters. The numerical solutions of Maxwell's equations are also compared with the popular H and Q empirical model.

Bistatic scattering and emissivities of random rough dielectric lossy surfaces with the physics-based two-grid method in conjunction with the sparse-matrix canonical grid method

Bistatic EM wave scattering from 2-D lossy dielectric random rough surfaces (3-D scattering problem) with large permittivity is studied. For media with large permittivities, the fields can vary rapidly on the surface. Thus, a dense discretization of the surface is required to implement the method of moments (MoM) for the surface integral equations. Such a dense discretization is also required to ensure that the emissivity can be calculated to the required accuracy of 0.01 for passive remote sensing applications. We have developed a physics-based two-grid method (PBTG) that can give the accurate results of the surface fields on the dense grid and also the emissivities. The PBTG consists of using two grids on the surface, the coarse grid and the required dense grid. The PBTG only requires moderate increase in central processing unit (CPU) and memory. In this paper, the numerical results are calculated by using the PBTG in conjunction with the sparse-matrix canonical grid (SMCG) method. The computational complexity and memory requirement for the present algorithm are O(N/sub scg/log(N/sub scg/)) and O(N/sub scg/), respectively, where N/sub scg/ is the number of grid points on the coarse grid. Numerical simulations are illustrated for root mean square (rms) height of 0.3 wavelengths and correlation length of 1.0 wavelength. The relative permittivity used is as high as (17+2i). The numerical results are compared with that of the second-order small perturbation method (SPM). The comparisons show that a large difference in brightness temperature exists between the SPM and numerical simulation results for cases with moderate rms slope.

Monte Carlo simulations of wave scattering from lossy dielectric random rough surfaces using the physics-based two-grid method and the canonical-grid method

In using the method of moments to solve scattering by lossy dielectric surfaces, usually a single dense grid (SDG) with 30 points per wavelength is required for accurate results. A single coarse grid (SCG) of ten points per wavelength does not give accurate results. However, the central processing unit (CPU) and memory requirements of SDG are much larger than that of SCG. In a physics-based two-grid method (PBTG) two grids are used: a dense grid and a coarse grid. The method is based on the two observations: (1) Green's function of the lossy dielectric is attenuative and (2) the free-space Green's function is slowly varying on the dense grid. In this paper, the PBTG method is combined with the banded-matrix iterative approach/canonical grid method to solve rough surface scattering problem for both TE and TM cases and also for near grazing incidence. We studied cases of dielectric permittivities as high as (25+i)/spl epsiv//sub 0/ and incidence angle up to 85/spl deg/. Salient features of the numerical results are: (1) an SCG has poorer accuracy for TM case than TE case; (2) PBTG-banded-matrix iterative approach/canonical grid BMIA/CAG method speeds up CPU and preserves the accuracy; it has an accuracy comparable to single dense grid and yet has CPU comparable to single coarse grid; (3) PBTG-BMIA/CAG gives accurate results for emissivity calculations and also for low grazing backscattering problems (LGBA); and (4) the computational complexity and the memory requirements of the present algorithm are O(N log(N)) and O(N), respectively, where N is the number of surface unknowns on the coarse grid.

Numerical solution of scattering of waves by lossy dielectric surfaces using a physics-based two-grid method

The numerical solution of the scattering of waves by lossy dielectric surfaces often requires a dense surface discretization of many points per wavelength. To reduce the CPU requirements, we have used a physics-based two-grid method (PBTG). In the method, we use two grids: a dense grid and a coarse grid of the usual ten points per wavelength. The method is based on the following two observations: 1) the Green's function of the lossy dielectric is heavily attenuative, and 2) the Green's function of free space is slowly varying on the dense grid. The method is illustrated with Monte Carlo simulations of scattering of waves by random rough surfaces of TE incidence. The examples illustrate the importance of using the dense grid for accurate results, and also the usefulness of PBTG in speeding up the calculations. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 16: 356–364, 1997.

Numerical solution of scattering of waves by lossy dielectric surfaces using a physics‐based two‐grid method

The numerical solution of the scattering of waves by lossy dielectric surfaces often requires a dense surface discretization of many points per wavelength. To reduce the CPU requirements, we have used a physics-based two-grid method (PBTG). In the method, we use two grids: a dense grid and a coarse grid of the usual ten points per wavelength. The method is based on the following two observations: 1) the Green's function of the lossy dielectric is heavily attenuative, and 2) the Green's function of free space is slowly varying on the dense grid. The method is illustrated with Monte Carlo simulations of scattering of waves by random rough surfaces of TE incidence. The examples illustrate the importance of using the dense grid for accurate results, and also the usefulness of PBTG in speeding up the calculations. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 16: 356–364, 1997.