摘要:

In some inverse problems that arise in detecting information about unknown structures we expect solutions that are piecewise continuous, for example, the problem of determining the size and shape of an orbiting satellite from backscattered far‐field measurement. Moreover, many of these problems are ill‐posed, which means among other things that accurate determination of solutions from noisy data is difficult, if not nearly impossible, unless special steps are taken. One class of methods dealing with these difficulties is regularization. In this paper, a regularization scheme is shown for finding an approximate solution of inverse problems which (a priori) possess piecewise continuous solutions. A numerical example is gi

ISSN:0048-6604    

DOI:10.1029/RS012i005p00637

年代:1977

数据来源: WILEY

摘要:

Analytical expressions are obtained for the mean‐squarenth moments of beam intensity profile, for the mean‐square perturbation of the spatial spectrum, and for the variance of intensity integrated over an aperture for finite beams propagating in turbulent media. The theory is based on the assumption of the existence of a phase autocorrelation which is a function of the transverse difference coordinates and is illustrated using the approximation of linear optics and the Rytov approximation. The theory can be applied to determine the capabilities of optical beam systems in the presence of turbule

ISSN:0048-6604    

DOI:10.1029/RS012i005p00643

年代:1977

数据来源: WILEY

摘要:

A simplified derivation and generalization of a design procedure due to Tseng and Cheng is presented. It permits determination of the discrete current distribution in a rectangular planar array corresponding to a sum pattern with a central main beam and concentric (but noncircular) ring side lobes, the latter having individually arbitrary heights. A practical example illustrates the theory.

ISSN:0048-6604    

DOI:10.1029/RS012i005p00653

年代:1977

数据来源: WILEY

摘要:

The diffraction of plane waves by two staggered parallel plates is investigated using the spectral diffraction coefficient in the Fourier transform domain. It is shown that when the interaction between the plates is negligible, the total field can be represented in terms of a double Fourier integral, a result that is identical to the one derived by Jones via the Wiener‐Hopf technique. The double integral is asymptotically evaluated via the saddle‐point integration technique and compact expressions for the field are derived, up to the orderk−1, for observation points located at the shadow boundaries and also away from the transition regions. These expressions are compared with the results of other asymptotic the

ISSN:0048-6604    

DOI:10.1029/RS012i005p00659

年代:1977

数据来源: WILEY

摘要:

It is proposed to describe the temporal characteristics of a wave propagating in a random medium in terms of its temporal moments. The first two moments are related to the mean arrival time and the mean pulse width. It is shown that the one‐position two‐frequency mutual coherence function enters in the formulation naturally. The form of the expression suggests expanding the mutual coherence function in a narrow‐band expansion whose coefficients can be solved exactly from the parabolic equation that takes into account all multiple scattering effects except the backscattering. A brief survey of the literature shows that the irregularity spectrum, under various conditions, has a power‐law dependence. In order to conform to this observation a Bessel function spectrum proposed by Shkarofsky is found convenient to use since it not only reduces to the desired power‐law form in the proper range of wavenumber space, but also has all the finite moments. Exact expressions for the mean arrival time and mean square pulse width are obtained; some numerical examples are given. Finally, the effect of noise on these moments is

ISSN:0048-6604    

DOI:10.1029/RS012i005p00671

年代:1977

数据来源: WILEY

摘要:

A theory of scattering from a weakly fluctuating random medium is formulated in terms of the effect of the background medium on the propagation of the incident and scattered waves. The nonrandom background medium is treated by a rigorous representation for electromagnetic waves interacting with a cylindrically symmetric, radially nonuniform plasma. The resulting boundary value problem is solved numerically using a 50‐layered approximation of the radial distribution. The scattering from the turbulent fluctuations, including depolarization effects, is calculated using existing theories that approximate the plasma by a weakly fluctuating refractive index except that the propagation in the background medium determines the local effective wavenumber and the weight factor for local turbulence scattering. This model is in good agreement with published data on microwave scattering from laboratory plasma where the microwaves do not interact with collisionless overdense regions in the plasma because of refractive effect

ISSN:0048-6604    

DOI:10.1029/RS012i005p00681

年代:1977

数据来源: WILEY

摘要:

The properties of two coupled horizontal‐wire antennas over a homogeneous isotropic halfspace are derived. The complex wave number, distribution of current, and admittance of the antennas are determined for symmetrical and antisymmetrical excitations. The wave number of the halfspace is assumed to be large in magnitude compared with that in air. The theory of the coupled horizontal‐wire antennas is extended to take account of radiation into the air and so enlarge its range of validity while preserving the transmission‐line form. This is accomplished by incorporating the effects of this radiation and of the capacitive end correction for the open end in a lumped terminal impedance which is conveniently represented by a complex terminal function. This function is determined from a least‐squares fit of the measured and the theoretical current distri

ISSN:0048-6604    

DOI:10.1029/RS012i005p00687

年代:1977

数据来源: WILEY

摘要:

An analysis of the propagation of electromagnetic waves along a perfectly conducting wire parallel to a plane interface between dissimilar materials is presented. Particular emphasis is placed on determination of the significance of the first‐order Fourier components of current on the wire compared with the zero‐order current which has no azimuthal dependence around the w

ISSN:0048-6604    

DOI:10.1029/RS012i005p00699

年代:1977

数据来源: WILEY

摘要:

A surface integral equation (SIE) technique is developed to analyze the scattering properties of arbitrarily‐shaped lossy dielectric bodies of revolution. Two coupled vector integral equations formulated via Maxwell's equations, Green's theorem, and the boundary conditions are used. The unknown surface currents (both electric and magnetic) are calculated by, first, Fourier decomposition, and then, the moment method, Galerkin's procedure. The far scattered field and radar cross section (RCS) are then readily determined from the reciprocity theorem and the measurement matrix concept. For a dielectric sphere good agreement is obtained between the SIE and exact solutions. Solutions of a thick dielectric cylinder are next used to demonstrate the arbitrary geometry capability of the SIE method. This method is suitable for homogeneous dielectric bodies and only the axially incident plane wave is considered here. The method also applies for a wide range of dielectric parameters (with ∈rfrom 1.44 to 80 and conductivity σ from 0 to 103mh

ISSN:0048-6604    

DOI:10.1029/RS012i005p00709

年代:1977

数据来源: WILEY

摘要:

Reflection of a vertically polarized electromagnetic plane wave from a periodic rough surface is considered. The surface is characterized locally by a boundary impedance. By using a perturbation analysis, a general expression is obtained for the amplitudes of the scattered waves which is valid for all spectral and all perturbation orders. It is shown that the results obtained here are consistent with earlier analyses of Rice, Wait, and Barrick. In addition, the general expression permits one to discern some important properties of the amplitudes for a purely sinusoidal surface. Among other things, we show that all odd perturbation orders are zero for the specular mode.

ISSN:0048-6604    

DOI:10.1029/RS012i005p00719

年代:1977

数据来源: WILEY