摘要:

The approach for handling transient electrodynamics problems based on their description by an integral Volterra equation is presented. The expression for a resolvent of this three‐dimensional space‐time vector equation for the case of a time‐varying dielectric restricted by a plane boundary is derived. Using this approach it is demonstrated that an oblique incidence of a plane monochromatic wave on a boundary of a dielectric whose permittivity changes abruptly in time leads to a formation of a continuous wave spectrum. In the case of a point source of electromagnetic radiation, the presence of a plane boundary leads to a replacement of a convergence point of secondary spherical waves to the mirror symmetrical point. The field in this point has a bounded value, as differentiated from the case of an unbounded m

ISSN:0048-6604    

DOI:10.1029/94RS03377

年代:1995

数据来源: WILEY

摘要:

A high‐frequency analysis of the reflection and diffraction of well‐focused electromagnetic Gaussian beams (GBs) by a perfectly conducting parabolic surface with an edge is presented for the two dimensional case. The fields are evaluated analytically via the physical optics (PO) approximation, and only the reflected field is expressed as a GB. The GB procedure developed here is expected to be highly efficient in applications involving large reflector antennas, since it avoids the conventional time‐consuming numerical evaluation of the PO integrals. Some numerical results are provided to indicate the accuracy of the analytical expressions obtained. The three‐dimensional case will be reported sep

ISSN:0048-6604    

DOI:10.1029/94RS03378

年代:1995

数据来源: WILEY

摘要:

Diffraction coefficients are derived from an approximate solution of the governing functional difference equations to characterize the scattering by an impedance wedge illuminated at skew incidence. This solution recovers the exact known diffraction coefficients for an impedance half plane and a wedge at normal incidence. To validate the approximate solution for other wedge angles, a comparison is made with numerical data obtained from a moment method code applicable to skew incidence on a polygonal impedance cylinder.

ISSN:0048-6604    

DOI:10.1029/94RS03015

年代:1995

数据来源: WILEY

摘要:

Full wave solutions are derived for vertically and horizontally polarized waves diffusely scattered across an interface that is two‐dimensionally rough separating two different propagating media. Since the normal to the rough surface is not restricted to the reference plane of incidence, the waves are depolarized upon scattering; and the single scattered radiation fields are expressed as integrals of a surface element transmission scattering matrix that also accounts for coupling between the vertically and horizontally polarized waves. The integrations are over the rough surface area as well as the complete two‐dimensional wave spectra of the radiation fields. The full wave solutions satisfy the duality and reciprocity relationships in electromagnetic theory, and the surface element scattering matrix is invariant to coordinate transformations. It is shown that in the high‐frequency limit the full wave solutions reduce to the physical optics solutions, while in the low‐frequency limit (for small mean square heights and slopes) the full wave solutions reduce to Rice's (1951) small perturbation solutions. Thus, the full wave solution accounts for specular point scattering as well as diffuse, Bragg‐type scattering in a unified, self‐consistent manner. It is therefore not necessary to use hybrid, perturbation and physical optics approaches (based on two‐scale models of composite surfaces with large and small roughness scales) to determine the like‐ and cross‐polarized fields scattered across

ISSN:0048-6604    

DOI:10.1029/94RS03163

年代:1995

数据来源: WILEY

摘要:

In this work full wave expressions are derived for the incoherent diffuse scatter cross sections (per unit area) for waves transmitted across rough surfaces. Both the like‐ and cross‐polarized cross sections are considered since the surfaces are rough in two dimensions. The full wave solutions are compared with the small perturbation solutions as well as with the physical/geometrical solutions. It is shown that when the heights and slopes are of the same order of smallness, the full wave solutions are in agreement with the small perturbation solution, while in the high‐frequency limit the full wave solution is in agreement with physical/geometrical optics solutions, provided that specular (stationary phase) points exist on the surface. Several illustrative examples are considered and the refractive index is assumed to be larger or smaller than unity. The critical angle for total internal reflection has a significant impact on diffuse scattering in the nonspecular direction. Since the full wave solutions account for specular point scattering as well as Bragg type scattering in a uniform, self‐consistent manner, it is not necessary to adopt the two‐scale model for the rough

ISSN:0048-6604    

DOI:10.1029/94RS03161

年代:1995

数据来源: WILEY

摘要:

A simple and computationally efficient methodology is demonstrated for treating the interaction of radio waves near grazing above rough surfaces. We apply it to the sea from HF through the microwave. Results using actual finite seawater conductivity depart significantly from those of a perfectly conducting profile for vertical polarization; for horizontal polarization there is essentially no difference. Shadowing behind wave crests is surprisingly shallow for vertical polarization even when the occluded depth is tens of wavelengths. This methodology gives expressions for the effective surface impedance at grazing as modified by the roughness when height scales greatly exceed the radio wavelength, augmenting prior expressions valid at HF for the sea obtained from perturbation theory. These effective impedances can then be used in formulations for radiation and surface wave propagation/diffraction at and below the horizon.

ISSN:0048-6604    

DOI:10.1029/95RS00835

年代:1995

数据来源: WILEY

摘要:

Field strengths of the beacon radio waves transmitted from the geostationary satellite ETS 2 are observed at a midlatitude station in Japan. Regular periodic variations in the field strength with a deep fade‐out at the central portion, called quasi‐periodic scintillations, are analyzed in terms of the minimum and maximum field strengths during each event. The variation in the field strengths is simulated with irregularity models for a variety of shapes, sizes, and electron densities. The numerical results are quantitatively compared with the observations and suggest that one type of quasi‐periodic scintillations is generated by linear irregularities that are elongated perpendicular to the drift direction, while the other type is generated by two‐dimensional, disk‐shaped irreg

ISSN:0048-6604    

DOI:10.1029/95RS00830

年代:1995

数据来源: WILEY

摘要:

A theoretical analysis of refractive loss of radio waves by the Earth's atmosphere in radio occultation measurements along the satellite‐to‐satellite line for various altitude profiles of the refractive index is given. Experimental results for refractive loss on the orbital spacecraft ‐ geostationary satellite link are presented. Theoretical calculations are compared with experimental data, and a conclusion is drawn that the signal amplitude during radio occultation is strongly dependent on the layered structure of the refractive index profile. Amplitude scintillations of centimeter (λ1= 2 cm ) and decimeter (λ2= 32 cm ) radio waves used in radio occultation experiments are described. Dependences of the rms value of the amplitude scintillations versus the minimum altitude of the ray line for the two above wavelength bands are presented. The frequency spectra of the log‐amplitude scintillations are analyzed together with the dependence of the rms amplitude on the wavelength. Experimental data are compared to the theory of scintillations in a turbulent atmosphere, and the altitude model of the structure constant of refractivity fluctuations is d

ISSN:0048-6604    

DOI:10.1029/94RS01920

年代:1995

数据来源: WILEY

ISSN:0048-6604    

DOI:10.1029/95RS01303

年代:1995

数据来源: WILEY

ISSN:0048-6604    

DOI:10.1029/94RS03185

年代:1995

数据来源: WILEY