摘要:

Full wave solutions are presented for horizontally polarized waves scattered by rough surfaces. Complete expansions and exact boundary conditions are used in the analysis. These solutions are compared with the physical optics solution based on the local tangent approximation of the fields at the irregular boundary. Expressions for the backscatter cross section for both horizontally and vertically polarized waves are also compared with earlier solutions to this problem. The reciprocity relationship and the suitability of the approximate impedance boundary condition are examined, and special consideration is given to excitation and scattering at grazing angles. This work on irregular ground effects on radio wave propagation can be applied to problems of communication, navigation, positioning, and active remote sensing.

ISSN:0048-6604    

DOI:10.1029/RS014i003p00341

年代:1979

数据来源: WILEY

摘要:

The two‐variable expansion technique is used to solve for the mean Green's functions from the Dyson equation under the nonlinear approximation for a half‐space random medium with three‐dimensional correlation functions. The Bethe‐Salpeter equations are then solved under the ladder approximation. The radiative transfer equations, which have been applied extensively in the study of microwave remote sensing problems, are derived under these approximations. The limiting cases of large and small horizontal correlation lengths are discussed. It is found that there is only one propagation constant except for the case of large horizontal correlation lengths, in which there are two propagation constants. We also show that boundary layer appears in first‐order solutions and does not appear in zeroth‐orde

ISSN:0048-6604    

DOI:10.1029/RS014i003p00359

年代:1979

数据来源: WILEY

摘要:

A technique is developed for retrieval of water vapor profiles from microwave radiometric measurements near the 183‐GHz water vapor line. Weighting functions are developed which are useful in the retrievals and which permit insight as to the information content in a given measurement. Retrievals are performed using synthetic dat

ISSN:0048-6604    

DOI:10.1029/RS014i003p00371

年代:1979

数据来源: WILEY

摘要:

A vector theory of wave scattering from a random medium has been developed using the first‐order renormalization theory. It is demonstrated with a chosen anisotropic correlation function that this first‐order theory can lead to cross‐polarized backscatter when the correlation function of the permittivity fluctuations is not required to have symmetry with respect to the plane of incidence. It is also found that while, in general, 12 modes may exist in the random medium (after excluding the evanescent modes), only two propagating modes are dominant and satisfy the radiation condition. When the correlation function is isotropic in the azimuth, there is no coupling between polarization components, and only one dominant propagating mode may exist for a given incident polarization. Approximate closed form expressions for the scattering coefficients are obtained for the anisotropic correlation function. The effects of anisotropy on the angular behaviors of the scattering coefficients are illust

ISSN:0048-6604    

DOI:10.1029/RS014i003p00377

年代:1979

数据来源: WILEY

摘要:

The modeling of a transient electromagnetic system as a single‐input, single‐output, linear, causal process is considered. Two canonical forms are discussed; one for impulse function input and the other for more general input. Expressions are derived for errors in the estimation of the model parameters caused by errors in the process data. It is shown that Prony's method is a special case of the impulse function model and that serious errors occur in attempts to apply the method in a noisy environment. It is also shown that least squares estimation of the model parameters produces biased results and that attempts to overcome this problem have led to nonlinear equation sets. Some recommendations are made concerning noise identification and filtering in order to improve resu

ISSN:0048-6604    

DOI:10.1029/RS014i003p00387

年代:1979

数据来源: WILEY

摘要:

Simple closed form expressions are obtained for the fields of an electric line source with transverse or longitudinal current flow parallel to and near the edge of a perfectly conducting wedge. The effect of an edge which is not perfectly sharp is investigated by considering a cylinder‐tipped half plan

ISSN:0048-6604    

DOI:10.1029/RS014i003p00397

年代:1979

数据来源: WILEY

摘要:

The diffraction of a TM0surface wave by a terminated dielectric slab which is flush mounted in a perfectly conducting surface is studied. The incident surface wave gives rise to waves reflected and diffracted by the termination; these reflected and diffracted fields may be expressed in terms of the geometrical theory of diffraction by introducing surface wave reflection and diffraction coefficients which are associated with the termination. In this investigation the surface wave reflection and diffraction coefficients have been deduced from a formally exact solution to this canonical problem. The solution is obtained via a combination of the generalized scattering matrix technique and the Wiener‐Hopf procedure. Expressions for the reflection and diffraction coefficients contain integrals which can be evaluated numericall

ISSN:0048-6604    

DOI:10.1029/RS014i003p00405

年代:1979

数据来源: WILEY

摘要:

An approximate asymptotic high‐frequency result which is convenient for engineering applications is obtained for the field exterior to a smooth perfectly conducting convex cylinder when it is illuminated by a plane wave. This result is uniform in the sense that it remains valid within the transition regions adjacent to the shadow boundaries where the pure ray optical solution based on the geometrical theory of diffraction (GTD) fails, and it automatically reduces to the GTD solution exterior to the transition regions where the latter solution becomes valid. Furthermore, this result is expressed in the simple format of the GTD, and it employs the same ray paths as in the GTD solution. This uniform result is not valid in the close neighborhood of the cylinder; hence a separate asymptotic result is presented for this special case in a form which is also convenient for applications. The asymptotic results presented here are useful for predicting the patterns of antennas radiating in the presence of convex conducting cylindrical structure

ISSN:0048-6604    

DOI:10.1029/RS014i003p00419

年代:1979

数据来源: WILEY

摘要:

The effect of coating a thin dipole antenna with a thin layer of magnetically and electrically lossy material is considered with respect to the properties of input impedance, current distribution, far‐field pattern, bandwidth, radiation efficiency, and effective length. Moment method calculations show that the change in the antenna properties is a strong function of the location and the kind of lossy material applied. The calculated input impedance of a monopole wrapped both fully and partially with different types of lossy materials is shown to agree well with measurements. An approximate semigraphical procedure for impedance calculation is postulated and shown to be usefu

ISSN:0048-6604    

DOI:10.1029/RS014i003p00437

年代:1979

数据来源: WILEY

摘要:

The observational evidence for long‐range propagation of high‐frequency radio signals began to accumulate in 1926 when transatlantic communication links were established. In 1927, signals were detected that had propagated over large distances or circled the earth with little attenuation. Long‐range and round‐the‐world (RTW) signals showed preferred periods of occurrence. Relatively high angles of incidence (20° relative to the horizontal) of such signals at the receiver paired with low attenuation ruled out conventional multihop propagation. An ionospheric refractive index boundary was postulated along which the signal propagates in a glancing incidence low‐loss mode. The transmission path of observed long‐delayed signals, originating from artificial earth satellites, was found to be located in the twilight zone. Experiments that used ground‐based transmissions confirmed the role of ionospheric absorption and tilts for the occurrence of long‐range and RTW signals. Detailed explanations for ionospheric ducting were provided by using several theoretical concepts and analyses. The μr(refractive index times geocentric distance) diagram was used for the study of ray propagation in a spherically stratified multilayered model ionosphere depicting characteristics of the ground‐detached glancing incidence mode. The potential well analysis was applied to an inhomogeneous slowly varying ionosphere. Numerical ray‐tracing computations were made by using model ionospheres with horizontal gradients. Ionospheric models were used to predict global properties of ionospheric wave channels. The role of scattering from natural and artificially induced ionospheric irregularities in long‐range ionospheric

ISSN:0048-6604    

DOI:10.1029/RS014i003p00447

年代:1979

数据来源: WILEY