摘要:

A multivariate K-distribution, well supported by experimental data, is proposed to model the statistics of fully polarimetric radar clutter of earth terrain. In this approach, correlated polarizations of backscattered radar returns are characterized by a covariance matrix and homogeneity of terrain scatterers is characterized by a parameter . As compared with C-, L- and P-band polarimetric SAR image simultaneously measured by Jet Propulsion Laboratory (JPL) on Mt. Shasta, it is found that appears to decrease from C- to P-band for both the forest and burned areas.

ISSN:0920-5071    

DOI:10.1163/156939391X00446

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A finite-difference time-domain (FDTD) method is used to solve the 21 2 D problem of the response of an arbitrary source, in particular, an impulsive point source, in a two-dimensional isotropic inhomogeneous medium. Cosine and sine transforms are used to reduce the three-dimensional problem to two dimensions. The complete solution is obtained by linearly superimposing several transformed field components. This provides great savings in terms of computer storage and run time over the three-dimensional FDTD model. A criterion is given to ensure the stability of this finite difference scheme. Examples of application of this analysis to actual problems such as the subsurface interface radar are illustrated.

ISSN:0920-5071    

DOI:10.1163/156939391X00455

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Recently there has been growing interest in the application of polarimetry to active microwave remote sensing of geophysical terrain. However, for passive microwave remote sensing, the third and fourth Stokes parameters were usually neglected in the past. In this paper, we make theoretical calculations of brightness temperatures of the third and fourth Stokes parameters for geophysical terrain. The calculations are based on vector radiative transfer theory with emission vector for random discrete scatterers. We also derive the reciprocal relations between emission of third and fourth Stokes parameters and the bistatic scattering coefficients for rough surface problems. Numerical results are illustrated. It is shown that brightness temperatures for third and fourth Stokes parameters can be as large as ±60°K for certain statistical asymmetrical configurations of scatterers.

ISSN:0920-5071    

DOI:10.1163/156939391X00464

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The problem of TM (transverse-magnetic) electromagnetic interaction with a slot-perforated conducting cylindrical shell is expressed in a generalized formulation and solved by the method of moments. The cylindrical shell is situated in free space and, in the general case, encloses a homogeneous material core. The solution uses two sets of fictitious filamentary electric current sources, with adjustable constant complex amplitudes, to simulate the fields in the two distinct regions of the problem. One set is used to simulate the field scattered by the cylindrical structure, while the other set is used to simulate the field penetrated the metallic enclosure through the slot. So constructed, the simulated fields produced by the filamentary sources are analytically derivable everywhere in space. We require these fields to obey the boundary conditions in the point-matching sense. This requirement is cast into a matrix equation which is in turn solved for the amplitudes of the filamentary currents. Once these filamentary currents are known, approximate values for the fields and field-related parameters of interest can be determined in a straightforward manner. The procedure is simple and general. A selection of illustrative examples is considered and compared with available data.

ISSN:0920-5071    

DOI:10.1163/156939391X00473

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We study the general scattering interaction of electromagnetic (EM) pulses of arbitrary shape and duration with a spherical target. The target is assumed penetrable and we model it either as totally dielectric, or as perfectly conducting but covered with a thin outer masking coating of a dielectric material. We obtain the radar cross-sections (RCS) of such targets and analyze the many resonance features that are present within their resonance region. The dielectric composition makes the resonance features become very prominent and it relates them to the eigenfrequencies in ways analogous to those of the Singularity Expansion Method (SEM), originally developed for perfectly conducting scatterers. Transient echoes from these targets are linked to poles and residues in the complex-frequency plane. The individual resonances associated with each pole (i.e., eigenfrequencies) can be studied one at a time, provided we use long illuminating pulses since these excite transients at their carrier frequencies that ring and decay. Of greater importance is the use of short pulses, since these are shown to replicate the entire RCS of the target in bands that have widths directly proportional to their energy and carrier frequency. We develop a methodology that can handle pulses of any conceivable spectra, interacting with (lossy or lossless) dielectric scatterers, and predict the backscattered returns. We illustrate it for various types of scatterers' compositions and/or pulses, with displays in the frequency and time domains, and give physical interpretations of the results.

ISSN:0920-5071    

DOI:10.1163/156939391X00482

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

In this paper we use the time dependent form of the electric field integral equation (EFIE) to solve transient scattering problems for perfectly conducting surfaces. In the computation of scattering from arbitrary surfaces the EFIE has the advantage of being applicable to both open and closed surfaces, whereas the magnetic field integral equation (MFIE) is applicable only to closed surfaces (i.e., solid bodies). On the other hand, for curved surfaces the EFIE is considerably more difficult to apply than the MFIE. This difficulty is primarily due to the occurrence of surface derivatives in the EFIE which are difficult to compute accurately on a curved surface. To overcome this problem in the frequency domain Rao et al. introduced a special set of basis functions defined on a triangular mesh on the surface. With these functions the appropriate derivatives are relatively easy to calculate, and the use of a triangular mesh on the surface means that general open or closed surfaces can be tackled. We use these basis functions together with a time marching method of moments technique to solve the time dependent EFIE. We utilise a particular testing procedure and an averaging technique to overcome the stability problems that time marching methods of solving integral equations are prone to.

ISSN:0920-5071    

DOI:10.1163/156939391X00491

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939391X00509

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor