摘要:

An experimental technique is developed to measure the modification of an electric field in a turbulent plasma. The method is suitable for use up to near critical density of the plasma. Measurements have been performed under three plasma conditions, namely, underdense, intermediate density, and near critical density. The results show more rapid attenuation of the coherent wave than predicted by exponential decrease, which is attributed to refraction in our nonuniform plasma column. The data indicate an initial buildup of the incoherent wave (both direct and cross‐polarized components) and then a decrease to a certain level depending on the equivalent thickness as the wave penetrates into the plasm

ISSN:0048-6604    

DOI:10.1029/RS012i002p00159

年代:1977

数据来源: WILEY

摘要:

Using modal expansions of electromagnetic fields in terms of prolate spheroidal wave functions, an exact formulation is presented for the scattering by a conducting prolate spheroid of a plane electromagnetic wave of arbitrary polarization and incidence angle. In this formulation the column vector of the series coefficients of the scattered field is obtained from the column vector of the series coefficients of the incident field by means of a matrix transformation. The matrix depends only on the scatterer; hence the scattered field for a new direction of incidence is obtained without repeatedly solving a new set of simultaneous equations. The exact curves numerically obtained for the monostatic radar cross section and relative phase of the scattered field as a function of aspect angle (angle of incidence) for both principal polarizations are given for a variety of prolate spheroids in the resonance region.

ISSN:0048-6604    

DOI:10.1029/RS012i002p00171

年代:1977

数据来源: WILEY

摘要:

The radiative transfer approach is used to study the thermal microwave emission from an inhomogeneous slab of random medium bounded by different dielectrics on both sides. The random medium can have nonuniform absorption, scattering and temperature profiles. With the method of invariant imbedding, the boundary value problem of the radiative transfer equations is cast into an initial value problem starting at zero slab thickness. The invariant imbedding equations so obtained are in the form of first‐order ordinary differential equations and incorporate the boundary conditions. Random fluctuations of a structure both laminar and with three‐dimensional variations are considered and illustrated. The frequency, angular, and polarization dependences of brightness temperatures are discus

ISSN:0048-6604    

DOI:10.1029/RS012i002p00185

年代:1977

数据来源: WILEY

摘要:

The theoretical model of an insulated antenna in a general ambient medium is reviewed briefly. Attention is then directed to the solution of the integral equation for the current distribution in the antenna. The properties of the kernel are discussed in detail, and approximate solutions for the complex wave number are obtained. The evaluation of the kernel and other related numerical problems are discussed and a numerical method of computation is presented. A discussion of approximate solutions is included. A comparison of the theoretical results with measured data and numerical computations is made to check the applicable range of the theory.

ISSN:0048-6604    

DOI:10.1029/RS012i002p00195

年代:1977

数据来源: WILEY

摘要:

The Kolmogorov hypothesis of an inertial range within the spectrum of steady state turbulence is used to show that the space‐time structure function for the velocity fluctuations in a fluid has the form of (r4/3+ ∈2/3t2)½whererandtare the space and time lags and ∈ the energy, for a reference frame in which the mean velocity is zero. The associated space‐time spectra are also derived. Equations for the propagation of theNevent space‐time correlation functions of the complex electric field are derived assuming that the width of the angular spectrum of plane waves is much less tha

ISSN:0048-6604    

DOI:10.1029/RS012i002p00205

年代:1977

数据来源: WILEY

摘要:

A theoretical study of a pair of TEM‐driven concentric annular slot antennas radiating through a perfectly conducting ground plane is described. The problem solution is accomplished in the rigorous Maxwell equation‐boundary value sense. Closed‐form solutions are obtained for the annular slot admittance and mutual coupling. These expressions include the effects of higher‐order TM modes which exist only in the evanescent state. Approximate solutions are obtained to a number of infinite coupling‐type integrals which are subsequently employed for numerical evaluation of the admittance and mutual coupling for several annular slot configurations. The effects to the annular slot admittance and mutual coupling are separable into those that are purely TEM induced and those that result from the presence of the beyond‐cutoff higher‐order TM modes. The analysis shows that the higher‐order mode perturbations are relatively minor provided that the width of the annular slots is less than one half wavelength. The method of analysis presented can be readily extended to multiple annular slot ring arrays under any set of TEM‐

ISSN:0048-6604    

DOI:10.1029/RS012i002p00213

年代:1977

数据来源: WILEY

摘要:

We have studied how the scintillation index is affected by the source bandwidth, the response time of the measuring instruments and the properties of the random medium. It is found that large‐bandwidth sources lead to a scintillation index other than unity in very strong turbulenc

ISSN:0048-6604    

DOI:10.1029/RS012i002p00223

年代:1977

数据来源: WILEY

摘要:

A formulation is given for the fields radiated by an electric or magnetic dipole of arbitrary orientation in the presence of a cable suspended above a flat and perfectly conducting ground. The cable can be a solid conductor, a leaky coaxial cable, a CATV cable, or a surface‐wave transmission line. Illustrative numerical results for both the far‐field radiation pattern and excitation of the modal currents on the cable are given for the case of a vertical electric dipole source. Among other things, we find that the resultant radiation or far fields are not markedly influenced by the presence of the cable unless the dipole source is very near the cable. However, there is a significant cross‐polarized component produced by the presence of cable that could have important consequences in producing bearing errors in low frequency beacon navigation sy

ISSN:0048-6604    

DOI:10.1029/RS012i002p00231

年代:1977

数据来源: WILEY

摘要:

The observation of atmospheric radio noise by use of the ARN‐2 recorder has been carried out since June 1967 at Ping‐Cheng. Using the data obtained from June 1967 to December 1972, the diurnal, seasonal, and solar cycle variations of the atmospheric noise power were investigated. The seasonal and solar cycle variations of the diurnal amplitude of the noise levels were also investigated. At 5 MHz, the diurnal amplitude of the noise power as well as the noise power at noon were found to be slightly dependent on the sunspot number. Comparison between the CCIR atmospheric noise predictions for Ping‐Cheng and the present observed results shows some differ

ISSN:0048-6604    

DOI:10.1029/RS012i002p00239

年代:1977

数据来源: WILEY

摘要:

We have applied the data‐inversion algorithms developed by investigators in the field of tomography to the problem of determining the structure of the ground between a pair of drill holes. The three most successful algorithms to date have been modified versions of the tomographer's ART (algebraic reconstruction technique), SIRT (simultaneous iterative reconstruction technique), and BPT (back projection technique). Projections were made by probing the ground with high‐frequency radio waves and recording the magnitude and phase of the received signal for various positions of transmit and receive antennas. The region between the holes was divided into rectangular zones (like a checkerboard). Ray‐optic approximations were made so that the equations describing the propagation between transmitter and receiver reduced to a linear system. The reconstruction technique algorithms were used to solve the system iteratively and assign appropriate values of skin depth to each zone. Simulations of a geological situation of interest were done to assess the sensitivity of the algorithms to noisy data. Then, measurements were taken in a coal field and the data were reduced using the ray‐optic assumptions and solution by the various alg

ISSN:0048-6604    

DOI:10.1029/RS012i002p00249

年代:1977

数据来源: WILEY