摘要:

The principles of a lightning location method using the VHF signals emitted by the discharge are outlined. Consideration of the source characteristics (notably signal strength and intervals between pulses; of the noise background; of the differences between the signals incident at spatially separated receivers; and of the electronic equipment now available commercially) indicate that the method is entirely feasible. For a lightning flash at a distance of 20 km, a spatial resolution of 200 meters, and a temporal resolution of 20 μsec could be readily obtained; consequently, the development of the successive VHF radiating events in the discharge could be traced

ISSN:0048-6604    

DOI:10.1029/RS004i003p00199

年代:1969

数据来源: WILEY

摘要:

Phase and amplitude records of 18.6‐kHz transmissions from NPG/NLK received at eight sites varying in distance from 4,360 to 13,420 km southwest of the transmitter, confirm the existence of a region within ±20° of the magnetic equator, in which VLF propagation parameters vary significantly from their midlatitude values. At all seven sites that involved transequatorial propagation paths, anomalies (including cycle slipping) were observed during the sunrise transition. The nature and temporal occurrence of these anomalies depended on the distance of the receiver from the magnetic equator. The experimentally derived dependence on magnetic latitude of the mode conversion ratio of the two least attenuated propagating modes and their apparent interference spacing are presen

ISSN:0048-6604    

DOI:10.1029/RS004i003p00203

年代:1969

数据来源: WILEY

摘要:

Weakly attenuated components of the VLF mode spectrum associated with propagation below highly anisotropic ionospheres are presented as a function of frequency and azimuth. In particular, results for the phase velocity, attenuation, polarization mixing ratio, and excitation factor for vertical dipole excitation are presented in the frequency range of 10–30 kHz for midlatitude paths, whereas azimuthal dependencies are presented for a frequency of 19.8 kHz and dip angles of 0° and 60°. The ionospheres are described by exponential electron density and collision frequency profiles, and the primary region of wave‐plasma interaction falls in the highly anisotropic region of the ionosphere. It is shown that polarization mixing is much more pronounced for a westerly propagation path than for an easterly path at midlatitudes, and, as a result, principally TE modes can be expected to influence the mode sum for frequencies at least as low as 20 kHz for propagation to the west. On the other hand, as has been shown previously, contribution to the mode sum by principally TE modes for propagation to the east becomes significant only near 30 kHz.Azimuthal anomalies include drastic polarization changes in going from easterly to westerly paths. For example, in the case of transverse propagation at the magnetic equator, it is shown that modes that are pure TM for propagation to the east may be pure TE for propagation to the west. Tantamount to this is the statement that modes that have dominant excitation for propagation to the east may have vanishing excitation for propagation to the west. Azimuthal dependencies are shown to be very often characterized by rapid variation of the mode constants in the neighborhood of north‐south or south‐north propagation. These variations manifest themselves in marked differences of the mode sum for azimuthal changes at least as small as 10°. Unfortunately, the azimuthal dependencies of the mode constants do not appear to lend themselves to any simple analytical appr

ISSN:0048-6604    

DOI:10.1029/RS004i003p00213

年代:1969

数据来源: WILEY

摘要:

Limitations of numerical maps of lower decile, median, and upper decile values of ƒ0E8derived for each month of both a solar cycle minimum and a solar cycle maximum year, and some applications to propagation problems are discussed briefly. The numerical map coefficients and contour charts for representative months and hours of the day in 1954 and 1958 are published

ISSN:0048-6604    

DOI:10.1029/RS004i003p00227

年代:1969

数据来源: WILEY

摘要:

Attention is drawn to similarities between certain magnetoionic formulas in ionospheric radio propagation and corresponding formulas for acoustic‐gravity waves. Acoustic waves are similar to radio waves with frequencies above the electron gyrofrequency, whereas gravity waves are similar to whistler

ISSN:0048-6604    

DOI:10.1029/RS004i003p00231

年代:1969

数据来源: WILEY

摘要:

A correlator supersynthesis array is defined as an array of antennas connected together in pairs as interferometers and capable of tracking a radio source during its apparent motion in the sky. Some problems in the design of such arrays are discussed. A computerized optimization technique, termed pseudodynamic programming, is described for the design of such arrays and some results are presented. The limitations and capabilities of the technique are discussed.

ISSN:0048-6604    

DOI:10.1029/RS004i003p00235

年代:1969

数据来源: WILEY

摘要:

Mutual coupling between the waveguides in finite arrays has been analyzed by using the integral equation method. Numerical solutions are obtained from which we find that the coupling in general decreases with the wavelength, as well as the distancesbetween the waveguides, and that for large separations the rate of decrease is inversely proportional tos½. However, when the waveguides are loaded with dielectric plugs, the characteristics of coupling may be substantially changed, owing to the excitation of modes that are propagating inside the dielectric but evanescent in the empty waveguide region. For example, the coupling may be greatly enhanced or suppressed depending on the choice of parameters such as the dielectric constant and plug thickness. In particular, it is found that under suitable conditions the coupling can exhibit resonance characteristics

ISSN:0048-6604    

DOI:10.1029/RS004i003p00245

年代:1969

数据来源: WILEY

摘要:

The classical Sommerfeld problem of electromagnetic wave propagation over a flat earth is reformulated by using the electromagnetic compensation theorem. The solution is carried through without recourse to the usual spectral representation of the potential function, and therefore complicated contour integrations are avoided in the subsequent evaluation. Using reciprocity and duality, the complete electromagnetic fields are calculated for elemental vertical or horizontal dipoles of both electric and magnetic types, which are elevated above an arbitrary but passive surface impedance such as that corresponding to homogeneous, horizontally stratified, or uniformly rough surfaces. The results are identical to the little known but more accurate work of Norton, and under certain approximations they reduce to the more well‐known results of Norton, Hufford, Bremmer, and others. The restrictions on the impedance properties of the surface are given, and certain direction finding errors are discussed. It is shown that the index of refraction contrast between the upper and lower medium need not be larg

ISSN:0048-6604    

DOI:10.1029/RS004i003p00255

年代:1969

数据来源: WILEY

摘要:

A cylindrical antenna is embedded in a dielectric cylinder, which is surrounded by a compressible isotropic electron plasma. The antenna impedance is formulated variationally by considering the effects of surface waves supported by the antenna structure. The surface waves alter the antenna current distribution for frequencies near the plasma frequency, but their amplitude is decreased as the thickness of the antenna insulation increases. The antenna solution is verified by examining the electric surface fields excited by the approximated antenna current distributions, and the results are compared with other numerical solutions.

ISSN:0048-6604    

DOI:10.1029/RS004i003p00269

年代:1969

数据来源: WILEY

摘要:

An analysis of the propagation of the mean or average plane wave in a compressible isotropic turbulent plasma is presented. It is shown that the average wave separates into a longitudinal and a transverse mode, and their dispersion relations are derived. The analysis is based on the first‐order smoothing theory in the form developed by Keller and assuming a Gaussian correlation function. It is found that mode coupling is a strong effect in the short correlation length region but becomes negligible for long correlation lengths. Useful approximations to the dispersion relations are also given for the short, intermediate, and long correlation length regions as well as numerical results for the perturbed propagation constant of the average transverse wave. The application of the theory to a random dielectric medium is pointed out and a quantitative evaluation of the importance of the depolarization term, i.e. the grad div term, in the vector Helmholtz equation is mad

ISSN:0048-6604    

DOI:10.1029/RS004i003p00279

年代:1969

数据来源: WILEY