摘要:

New improvements to compute Mie scattering quantities are presented. They are based on a detailed analysis of the various sources of error in Mie computations and on mathematical justifications. The algorithm developed based on these improvements proves to be reliable and efficient, without size (x = 2 nor refractive index (m = mR- imI) limitations, and the user has a choice to fix in advance the desired precision in the results. It also includes a new and efficient method to initiate the downward recurrences of Bessel functions.

ISSN:0920-5071    

DOI:10.1163/156939391X00950

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

This communication focuses on the effective permittivity of a mixture that consists of a background medium in which layered spherical scatterers are randomly embedded. For dense nontenuous media, the quasicrystalline approximation has to be supplemented with the coherent potential approach. For the effective permittivity or the effective propagation constant, two theories have been published [1,2]. This paper compares the predictions of these theories and proves that they are consistent.

ISSN:0920-5071    

DOI:10.1163/156939391X00969

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Passive corner reflectors are used to find the system transfer functions relating the amplitudes of a SAR image to ° values and to derive receiver and transmitter characteristics of a multichannel polarimetric SAR from the complex image data. Results are presented from the 1989 airborne SAR calibration campaign at DLR test site Oberpfaffenhofen. The sensors available were the DLR E-SAR operating in C-Band/VV mode and the NASA/JPL multifrequency multipolarization DC-8 SAR.

ISSN:0920-5071    

DOI:10.1163/156939391X00978

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Two mathematical techniques - scalarization and symbolic technique - are promoted as useful techniques for the solution of dyadic differential equations. Both are employed to find a complete, analytic inversion of the dyadic differential operator × x I - a2I - b × I. An operator of this structure arises in the electromagnetic theory of isotropic chiral media. While describing the identical physical process, different mathematical formulations of chiral media have been put forward in the literature. The operator (and therefore the dyadic Green's function) analyzed here is the most general one that contains the other descriptions as special cases of the parameters.

ISSN:0920-5071    

DOI:10.1163/156939391X00987

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The electromagnetic inhomogeneous pulses are solutions of the wave equation with boundary data on a wave front. They propagate without distortion but their energy is infinite, at least for the most interesting of them. This suggests looking for approximate pulses with finite energy and with a distortion as small as possible. It is shown that this result can be obtained with boundary data given in a moving plane.

ISSN:0920-5071    

DOI:10.1163/156939391X00996

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Polarimetric radar measurements are corrupted by numerous error sources which limit the ability to derive true scattering coefficient information. The coupling between the polarimetric channels, gain imbalance between channels, and the influence of the system noise floor may all have detrimental impact on the measurement accuracy. These error sources and the relative impact of each of them will differ from radar to radar. Also, the impact of the error sources is dependent on the true scattering properties that are being measured. The importance of each of the error sources is examined by a perturbation study. Then the error effects are quantified by determining the worst-case error as a function of radar parameters and scatterer parameters. These worst-case distortion errors will be discussed along with the practical limits for removing the various sources of error.

ISSN:0920-5071    

DOI:10.1163/156939391X01003

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The scattering of electromagnetic radiation from a finite conducting cylinder with complex permittivity at an arbitrary orientation was analyzed using a first approximation to the iteration technique for the integro-differential equation first developed by Shifrin and later modified by Acquista. The classical Kerker solution for a simple infinite dielectric cylinder was extended to a more physically realistic solution accounting for a finite length cylinder with complex permittivity by a modified Drude conductivity approach. The diameter of the cylinder is on the order of one wavelength of the incident radiation. The lowest order approximation to the internal field solution for the iteration process is a function of the effective polarized electric field inside the cylinder and the polarization matrix of the scattering medium. The polarization matrix of the cylinder is determined from the electrostatic solution for a finite cylinder in a constant electric field, and is a function of the length to diameter ratio (aspect ratio) and the permittivity of the cylinder. The electrostatic solution for a finite cylinder does not permit a closed solution; therefore the cylinder is approximated by an inscribed ellipsoid which provides a converging analytic expression. Results are compared to published data. The complex frequency dependent permittivity of the cylinder material was modeled using a modified Drude conductivity approach. The effects of typical variations in the length, diameter, and bulk conductivity of the cylinder were analyzed for TE, TM and TEM polarizations.

ISSN:0920-5071    

DOI:10.1163/156939391X01012

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Microwave radiopolarimetry is applied to remote sensing of azimuthally asymmetric features on Earth terrain. The first three components in the brightness-temperature modified Stokes vector are measured for a triangularly corrugated soil surface. The measurements are made at 10 GHz with horizontal, vertical, and 45° orientations. Significant values of the third Stokes brightness temperature UBare observed in various configurations. A theoretical analysis of the data incidates that the appreciable values of UBare caused by the azimuthal asymmetry on the remotely sensed soil surface.

ISSN:0920-5071    

DOI:10.1163/156939391X01021

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The theory of electromagnetic sounding of the earth, based on interference effects in the spatial structure of a pair of coupled waves, propagating along the earth's surface with the same frequency but different wavelengths, is proposed. A hitherto unknown heterogeneous structure of surface impedance, the conductivity being constant, is analysed by means of new exact analytical solutions of Maxwellian equations, described by the propagation of coupled waves from the source along the boundary between two media, the complex dielectric permittivities of both media being arbitrary. The classical formulae for Biot-Savart law and VLF impedance of conducted surface prove to be the private causes of obtained interference structure, related to the limit values of parameters. The perspectives of use of amplitude-phase effects of interference pattern, generated by direct and lateral waves, for earth sounding, especially for undersea sounding, are illustrated.

ISSN:0920-5071    

DOI:10.1163/156939391X01030

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We consider the diffraction problem of a scalar plane wave incident upon an array of semi-infinite cylinders whose parallel axes lie at the vertices of a regular polygon. For the Dirichlet boundary condition and under the assumption of small radii and large inter-element spacings, an exact solution to the problem is obtained by means of the Wiener-Hopf technique. Far field expressions are derived and the approximate evaluation of some difficult integrations given. Results are presented for axial incidence on double, triangular and square arrays.

ISSN:0920-5071    

DOI:10.1163/156939391X01049

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor