摘要:

By using the Born approximation and the Gaussian model for the correlation of refractive index fluctuations in the atmosphere, an expression for the power in the first‐scattered field of the TEM∞mode is obtained. It is demonstrated that the second‐scattered field does not contribute to beam broadening in the lowest‐order approximation. The total power in the first‐scattered field is found. The transverse profile of the scattered power is shown to be a function of a single parameter ΘL, which depends strongly on the ratio of the beam radius to the scale of turbulencea/lo. Values ofloand the mean square fluctuation of the refractive index (n12) are determined in an illustrative comparison with experimental data of the theoretical profile of a broa

ISSN:0048-6604    

DOI:10.1029/RS004i011p00983

年代:1969

数据来源: WILEY

摘要:

The Helmholtz integral theorem for the scattering or radiation of radio waves from surfaces is examined to obtain a more general approximation of the observed field distribution. The resulting new integral expansion is particularly responsive to evaluation by the method of stationary phases, yielding a quantitative solution applicable to a more general class of surfaces and aperture boundaries than was previously feasible. The problem of reflection from finite irregular surfaces, such as terrain or atmospheric layers, is evaluated formally. The result indicates a source of significant reflections not generally treated by ray theory.

ISSN:0048-6604    

DOI:10.1029/RS004i011p00991

年代:1969

数据来源: WILEY

摘要:

A new, vectorial, approximate solution is presented for a particular class of problems: that of a vector wave propagated through a linear, isotropic, piecewise‐homogeneous medium with irregular interfaces and boundaries. This class of problems lacks not only an exact method of solution but also a reliable method of approximation for tropospheric radio propagation at VHF and higher frequencies. A method is proposed that incorporates a recent expansion of the Helmholtz integral to evaluate the Stratton‐Chu integral by the methods of stationary phase. To demonstrate its potential, the method is applied to two of the simplest thin‐screen pro

ISSN:0048-6604    

DOI:10.1029/RS004i011p00997

年代:1969

数据来源: WILEY

摘要:

Solutions of the continuity equation for electrons in theF2region of the earth's ionosphere are obtained by including parameters for the various physical processes experienced by the plasma moving in the electromagnetic‐drift frame of reference. The electric field responsible for such a drift is derived from an electric potential, so the E X B/B2drift velocity has an east‐west component in addition to the usual vertical one. The Jacchia model atmosphere is used, and the description of the photoionization process uses the Chapman function for absorption of radiation by the neutral atmosphere. The ratio of electron temperature to ion temperature can be varied with time. Account is taken of recombination with both molecular oxygen and molecular nitrogen. Other processes included are diffusion and neutral air winds. The velocity of the neutral air winds is assumed to be zero at the equator for equinox conditions and at 15° latitude reaches a maximum of 35 m sec−1directed away from the equator at 1300 LT and a maximum of 55 m sec−1directed toward the equator at 0100 LT. It is shown that the east‐west component of the electromagnetic drift has little effect on the solutions. For sunspot‐minimum atmospheric conditions, better agreement with observations in the equatorial region is obtained when the vertical component of the electromagnetic drift velocity peaks at noon rather than at 1500 LT. The sunspot‐maximum results show that there is a phase difference in the electromagnetic drift between sunspot‐maximum and sunspot‐minimum conditions. The over‐all magnitudes of equatorialNmF2agree fairly well with observations for both sunspot‐minimum and sunspot‐maximum conditions. The equatorward wind at night is a necessary feature to maintainNmF2at its observed levels at latitudes higher than about 10°. Within 10° of the equator winds do not play an essential role in the maintenance of the nighttime ionosphere. Preliminary results for a moderate latitude field line with a model variation ofTe/Tishow several features that are in accordance with Evans' data for the period when the eve

ISSN:0048-6604    

DOI:10.1029/RS004i011p01005

年代:1969

数据来源: WILEY

摘要:

Johler has pointed out an error in a previous derivation of the wave‐hop series for an anisotropic ionosphere. The error, which results in inaccurate field strengths for some ionospheric models (especially at night), is corrected in this pape

ISSN:0048-6604    

DOI:10.1029/RS004i011p01025

年代:1969

数据来源: WILEY

摘要:

The HF propagation loss behavior, in general, and the observed losses over the north‐south path reported here, in particular, can be explained in terms of a deterministic and a random component. Thus, the results are presented as the cumulative distributions of loss by frequencies and by modes in terms of their median and decile values. The most significant aspect of these data and the accompanying statistics is that the propagation losses were observed and analyzed strictly on the individual mode basis. Among these propagation modes are included 2‐hopE, 1‐hopF2, 2‐hopF2, 2‐hopE8, and N. From the medians and the deciles of the loss distributions of these various modes, it is quite apparent that propagation losses are mode dependent, day and night dependent, and sometimes high‐ and low‐ray dependent. TheE‐mode losses also appear to be dependent on the ratio of the operating frequency and the maximum observed freque

ISSN:0048-6604    

DOI:10.1029/RS004i011p01029

年代:1969

数据来源: WILEY

摘要:

The way in which a mechanical lock‐on type of direction finder of small aperture can be used for recording the variations of incoming wave‐normal direction in both the vertical and horizontal planes is discussed. The limitations arising from the inertia of the system are considered. It is shown that, in the case of near‐antipodal short‐wave ionospheric propagation (Great Britain to New Zealand), the received cone of rays usually contains two or more main groups displaced in angle in a plane that is nearly v

ISSN:0048-6604    

DOI:10.1029/RS004i011p01039

年代:1969

数据来源: WILEY

摘要:

The ground surface exhibits a varying conductivity for different horizontal directions. It is excited by vertically or horizontally polarized waves. The ground produces a coupling between TM and TE field components. The net horizontal fields are modified by the anisotropy, except for the horizontal magnetic fields of the TM modes, which remain the same as under isotropic conditions; the horizontal electric fields are decreased near the directions of higher ground conductivity. The resulting pattern distortions of a horizontal wire antenna are explained by using simple closed‐form expression

ISSN:0048-6604    

DOI:10.1029/RS004i011p01047

年代:1969

数据来源: WILEY

摘要:

The problem of specifying the minimum magnitude of the maximum electric field over an azimuthally symmetric slotted cylinder subject to the constraint of a specified radiated power into a given wedge angle is treated. Aperture bounds are presented for both the TE, TM and the general TE/TM excitation of the slot. The degree to which these bounds are attainable is discussed, and their relationship to uniform illumination of the aperture is examined. The problem of synthesizing a specified field pattern over the given angle is also treated.

ISSN:0048-6604    

DOI:10.1029/RS004i011p01061

年代:1969

数据来源: WILEY

摘要:

The mean field is considered for a bounded medium with a refractive index having a real random part. It has been shown previously that for suitable ranges of the amplitude and correlation length of the refractive index fluctuations, this field satisfies a certain integrodifferential equation. This equation is solved for a plane wave incident from either side on the plane boundary of a semi‐infinite random medium, for the Green's function of a semi‐infinite random medium, and for a plane wave incident on a slab of random medium, provided that the background refractive index is homogeneous throughout. The cases of both one‐ and three‐dimensional fluctuations are considered, and explicit expressions are given for the reflection,transmission, and coupling coefficients for a medium with an exponential correlation function.A Wiener‐Hopf factorization required for other correlation functions is described, as are methods for treating reflection and transmission at a curved boundary of a random medium. A principal finding is the inadequacy of treating the mean wave in a bounded random medium by using just the refractive index for an unbounded random medium, for in addition we must include a transition layer near the

ISSN:0048-6604    

DOI:10.1029/RS004i011p01067

年代:1969

数据来源: WILEY