摘要:

The reflection coefficients at normal incidence are found for a large class of one‐dimensionally inhomogeneous or stratified half‐spaces, which contain a homogeneous half‐space. The formulation of the problem involves a combination of the classical boundary value technique, and the nonclassical principle of invariant imbedding. Solutions are in closed form and expressible in terms of Bessel functions. All results are given in terms of the ratio of the distance between free space and the homogeneous half‐space to the wavelength in vacuo. One special case is that of an arbitrary number of layers lying on a homogeneous half‐space where the dielectric constant of each layer has a constant gradient. A number of other special cases, limiting cases, and generalizations are developed including one in which the thickness of the top layer obeys a probability distribution, and another formulation that is computationally efficient in which there is an extremely small change in the dielectric constant such as with atmospheric inversi

ISSN:0048-6604    

DOI:10.1029/RS008i012p01083

年代:1973

数据来源: WILEY

摘要:

The technique called “modulated pulse” (the emission of HF pulses of suitable length modulated with high or low audiofrequencies) allows an exhaustive study of the propagation of modulated radio waves in the ionosphere. Using this system it is possible to establish that the diminution or the gain, in regard to that emitted by the transmitting antenna, of the percentage of modulation of the received modulated waves is not due in any way, as some researchers have declared, to the interference in the receiving antenna of rays that have travelled different paths in the ionosphere or to multiple echoes, but should be attributed to other reasons.The experiments were made with carrier frequencies varying around the cyclotronic frequency and with different modulation frequencies. It was possible to obtain either a resonance curve of demodulation or a resonance curve of overmodulation and it was shown that the selective fading could be obtained with low frequencies as well as with high frequencies of modulation. The most important contribution herein is the determination that the interference does not alter in any way the depth of modulation of a modulated wave provided that the envelopes remain undistorted. If the amplitude of the echo is less than the minimumB, as generally happens, the interference never alters the sinusoidal form of the envelope. If the amplitude is greater the envelope always becomes distor

ISSN:0048-6604    

DOI:10.1029/RS008i012p01093

年代:1973

数据来源: WILEY

摘要:

The relations between electron content, scintillation, and radio absorption are studied at an auroral zone station. It is found that during absorption events, indicating particle precipitation, the level of scintillation increases and the electron content increases in winter but is unchanged or slightly decreased in summer. At a given level of scintillation, the absorption is greater on a winter day than on a summer day. Although some of the observations are consistent with the results of other investigations, full explanations are lacking. It seems clear that, in addition to direct ionization production by auroral particles, other mechanisms must be involved. Further studies based on reception of geostationary satellite transmissions are recommended.

ISSN:0048-6604    

DOI:10.1029/RS008i012p01111

年代:1973

数据来源: WILEY

摘要:

Ionospheric refraction is one of the factors limiting the accuracy of radar systems tracking objects in or beyond the ionosphere. In advanced systems it may be desirable to perform accurate corrections for these effects in real time, and because of the extreme variability of the ionosphere, this presupposes real time, local ionospheric measurements, e.g., by a modern digital ionosonde. The ionosonde could then be required to monitor the state of the ionosphere, compare it with model conditions, and forecast the radar refraction environment in real time. One component in this problem is the calculation of the radar refraction effects, given the ionospheric electron density profile, the apparent radar range, and look angle. Assuming that the electron density depends on height only, this paper describes such a procedure suitable for use within the Dynasonde or a similar digital ionosonde interfaced to an active radar system.

ISSN:0048-6604    

DOI:10.1029/RS008i012p01119

年代:1973

数据来源: WILEY

摘要:

The propagation of high frequency electromagnetic waves through an ionosphere perturbed by a gaussian electron density trough is investigated using a three‐dimensional ray‐tracing computer program. Ray trajectories are presented for a normalized model ionosphere with troughs of varying width, depth, and distance from the transmitter. Focussing and defocussing effects are demonstrated to occur under special circumstances. Particular emphasis is placed upon simulation of records from fixed‐ and swept‐frequency sounding equipment. In particular, a moving trough is found to have unique Doppler signature which may be useful for ground‐based observati

ISSN:0048-6604    

DOI:10.1029/RS008i012p01125

年代:1973

数据来源: WILEY

摘要:

Natural radio noise received by the ISIS satellites in the polar and auroral regions often exhibits spin modulation. For noise in the whistler‐mode frequency domain observed on seven high‐latitude passes, the data indicate that temporal‐spatial variations in the level of the noise source are not important on a time scale of one spin period, and thus the dependence of the signal on the attitude of the receiving dipole antenna can be studied. Relative variations in level during one half of a spin period have been synthesized by simply convolving the attitude dependence of the antenna impedance with a spatial distribution of electric vectors. The resonance cone angle, corresponding to the infinity in the refractive index, has been predicted to an accuracy of 3°, while the theoretical amplitude and shape of the modulation agree well with what is observed. It is found that longitudinal electric waves yield better agreement than transverse electromagnetic waves. In some cases, preferred horizontal propagation directions can be roughly identified. The computations confirm the relevance of established theory for the antenna impedance and the ion

ISSN:0048-6604    

DOI:10.1029/RS008i012p01133

年代:1973

数据来源: WILEY

摘要:

Radiation from a slot antenna surrounded by a plasma sheath moving parallel to an external magnetostatic field is considered. It is shown that the radiation pattern is inclined in the direction of the sheath motion as the velocity is increased except for the case where the condition of upper hybrid resonance is satisfied in the rest frame of the plasma. When such a relativistic upper hybrid resonance caused by the sheath motion arises for certain values of normalized plasma and cyclotron frequencies and the velocity parameter, a deep null and a rapid oscillation appear in the radiation pattern, and as a result the shape of the pattern is extremely deformed.

ISSN:0048-6604    

DOI:10.1029/RS008i012p01149

年代:1973

数据来源: WILEY

摘要:

A method is proposed by means of which the propagation constants and field components may be obtained for the surface waves supported by symmetrically inhomogeneous dielectric layers. The specific profile shape of the permittivity across the layer is nearly arbitrary. The characteristic equations from which the propagation constants for the even and odd TE and TM modes are obtained are expressed directly in terms of the Fourier expansion coefficients of the permittivity variation, and the field components are expressed in terms of solutions to the Hill equation. Numerical results are presented to illustrate the analysis for a specific family of dielectric profiles.

ISSN:0048-6604    

DOI:10.1029/RS008i012p01157

年代:1973

数据来源: WILEY

摘要:

Branch‐cut integrals are used to calculate the reflection of transient pulses from the surface of a cold, lossy, semi‐infinite plasma. For the case considered in detail, small to moderate losses and an impulse‐incident waveform with transverse magnetic polarization, the reflected waveform is oscillatory for small losses (collision rate much less than the plasma frequency) but decays monotonically for a collision rate of half the plasma frequency. The reversal of polarity of the initial half cycle of the reflected waveform observed as the incidence angle increases through 45° is interpreted as a Brewster‐angle ph

ISSN:0048-6604    

DOI:10.1029/RS008i012p01165

年代:1973

数据来源: WILEY

摘要:

The boundary value problem posed is a truncated cylindrical region excited by a specified distribution of electric current over a concentric cylindrical surface. The end conditions are that the total normal current density is zero. The solution is carried through for excitation by a symmetrically located axial current filament that is adjacent to the cylinder. Numerical results of the resultant magnetic field are given for the quasi‐static situation for a perfectly conducting cylinder. It is indicated that the results depend significantly on the length of the cylindrical target. Even for very long cylinders, there is no quantitative similarity with the corresponding two‐dimensional model of a cylinder of infinite len

ISSN:0048-6604    

DOI:10.1029/RS008i012p01169

年代:1973

数据来源: WILEY