摘要:

Measurements of apparent resistivity and phase derived from the complex surface impedance of radio waves propagating in the ground wave mode at frequencies in the radio navigational aid band (between 257 and 382 kHz) are presented. Areas encompassing between 400 and 800 km2that covered a variety of glacial sediments, land forms, and some crystalline bedrock types were surveyed. The results show that (1) loess was commonly between 20 and 40 ohm m with phases between 50° and 60°, (2) end moraines had a wide dispersion with values generally ranging between 20 and 1000 ohm m and 40° and 80°, (3) metamorphic phyllites and schists were generally between 100 and 3000 ohm m with an average near 1000 ohm m and phases usually well below 45°, and (4) granites were the most resistive at an average value of about 2000 ohm m with the lowest phases averaging 12°. The degree of dispersion in resistivity values reflects the dispersion in grain size, while the average resistivity increases with mean grain size. Dielectric properties are suggested as one cause of the low phases observed over crystalline bedrock. The combination of apparent resistivity and phase data implies that the resistivity measurements are consistent in about 50% of the areas with previous measurements of field strength attenuation performed in the AM broadcast

ISSN:0048-6604    

DOI:10.1029/RS015i001p00001

年代:1980

数据来源: WILEY

摘要:

The theory of propagation of electromagnetic waves in layered plasmas with Epstein type density gradients is investigated. Depending on polarization, the presence of a nonzero magnetic field and the angle of incidence with respect to the gradient, the number of regular singular points is determined, and thus the type of relevant Fuchsian equation is indicated.

ISSN:0048-6604    

DOI:10.1029/RS015i001p00011

年代:1980

数据来源: WILEY

摘要:

The problem of excitation of the modified Goubau line from a coaxial junction is analyzed using the Wiener‐Hopf technique and Fourier transforms in the axial direction. The analytical expressions reduce to those of Ledeboer in the absence of the air gap. The effects of the air gap in reducing the input reflection coefficient and in modifying such other parameters as the launching efficiency and propagation constants for different frequencies are illustrated with numerical example

ISSN:0048-6604    

DOI:10.1029/RS015i001p00017

年代:1980

数据来源: WILEY

摘要:

The oxygen spectrum near 60 GHz is studied empirically with emphasis on its application to the passive remote sensing of the tropospheric and lower stratospheric temperature. For this purpose the oxygen absorption coefficient over a certain range of pressurepand temperatureTis fitted to the power law formapxTy, wherea, x, andyare frequency‐dependent parameters. A root‐mean‐square relative error of 8% is obtained by best fitting the parameters to the theoretical absorption expressions proposed by Van Vleck and Weisskopf, Gross, and Rosenkranz. This provides a convenient basis for a quantitative comparison of the three theoretical expressions. The power law form also leads to a basic understanding of the remote sensing of the atmospheric temperature profile from airborne spectrometers. Such concepts as height selectivity and resolution can be naturally defined in terms ofa, x, y, and the pressure scale height of the atmosphere. As a practical application it is shown how the power law form can help attack the forward and inverse problems in remote sensing. An example is given in treating satellite data from the Nimbus 5 microwave spectro

ISSN:0048-6604    

DOI:10.1029/RS015i001p00025

年代:1980

数据来源: WILEY

摘要:

We present theory to show that errors in lightning magnetic direction finding due to nonvertical source orientations are minimized by detecting the field from the lowest possible channel section. For 99 cloud‐to‐ground lightning channels photographed in Arizona, 45 exhibited a bottom few hundred meters within about 8° of the vertical, the standard deviation of the distribution of lower‐channel tilt angles being about 18°. These experimental results, coupled with theory, suggest that if a wideband gated direction finder is used, polarization errors due to nonvertical sources can be kept less than 1° for lightning beyo

ISSN:0048-6604    

DOI:10.1029/RS015i001p00035

年代:1980

数据来源: WILEY

摘要:

In this paper, numerical computations of the intensity spectral density function of a wave field scattered by a one‐dimensional, power law phase screen are presented. The computations verify theoretically derived asymptotic results showing that when the power law index is greater than three, the scintillation index saturates at a value larger than unity. Moreover, strong focusing, a local maximum in the scintillation index variation with increasing perturbation strength, only occurs in a one‐dimensional medium when the spectral index is greater than or equal to 3. The application of these results to the interpretation of radiowave scintillation data is discus

ISSN:0048-6604    

DOI:10.1029/RS015i001p00041

年代:1980

数据来源: WILEY

摘要:

The potential created by a current pulse is derived using a warm‐plasma description in the vicinity of the lower hybrid resonance (LHR). The results are somewhat different from the previous ones obtained with the cold‐plasma theory; the amplitude of the excited wave has an asymptotic decay with time ast−1rather thant−½. The spatial distribution of the potential shows a propagation effect that gives a reasonable explanation of the duration of the VLF echoes excited by the Isis 2 HF transmitter; it might also provide a technique for the measurement of the ionic thermal velocity and the drift velocity component perpendicular to the magnet

ISSN:0048-6604    

DOI:10.1029/RS015i001p00049

年代:1980

数据来源: WILEY

摘要:

The long‐term VHF scintillation data from ATS 3 obtained at three stations situated in the North Atlantic sector at auroral and subauroral locations during the period 1968–1974 are used to determine the morphology of high‐latitude scintillations near the 70°W longitude sector. The variation of the average level of scintillation at each observatory is studied as a function of time of day, season, and magnetic activity in a manner suitable for incorporation into statistical models of scintillation occurrence. The most prominent feature of the data is a seasonal dependence of scintillations with a 2:1 variation from northern summer to winter under quiet magnetic conditions. This also causes a large variation in the latitudinal gradient of scintillations from 2 dB per degree in summer to 1 dB per degree in winter for latitudes>60° invariant. The observed seasonal control of scintillations is related to the variation of the tilt angle of the earth's magnetic dipole and consequent modulation of the particle precipitation in the North Atlantic sector of the auror

ISSN:0048-6604    

DOI:10.1029/RS015i001p00059

年代:1980

数据来源: WILEY

摘要:

A series of measurements of the properties of equatorial ionospheric irregularities were made at Kwajalein, Marshall Islands (M.I.) in August 1977 and July–August 1978. These measurements, sponsored by the Defense Nuclear Agency (DNA), involved coordinated ground‐based and in situ sensors. The ARPA Long‐Range Tracking and Instrumentation Radar (ALTAIR), operated by Lincoln Laboratory, obtained backscatter and transmission data during five nights in August 1977 and eight nights in July–August 1978. This report describes the ALTAIR data from the night of August 11, 1978, which yield direct quantitative measurements of 1‐m and ⅜‐m irregularities and of plasma depleted regions. These plasma depleted regions, previously predicted on the basis of theoretical analysis and in situ data, were observed during the decay phase and not the generative phase of the field‐aligned

ISSN:0048-6604    

DOI:10.1029/RS015i001p00071

年代:1980

数据来源: WILEY

摘要:

Numerical and analytical solutions for the backscattered pulse shape from a slab of random medium are given based on the cumulative forward‐scatter single‐backscatter (CFSB) approximation given by deWolf, assuming small angular‐spread and a narrow‐band incident pulse. The analytic solutions for asymptotic limits for extreme small‐angle scattering are also obtained. The results are applicable to both discrete media with large particles and continuous media with a large scale of t

ISSN:0048-6604    

DOI:10.1029/RS015i001p00087

年代:1980

数据来源: WILEY