摘要:

A solid state microwave refractometer was mounted in a Royal Australian Air Force Dakota aircraft in order to measure vertical profiles of the atmospheric radio‐refractive index over the Timor Sea at times of anomalous radio wave propagation. Computer raytracing techniques, applied to model atmospheres based on these measurements, have indicated the importance of tilted layers in the tropospheric ducting of short‐wave radio ene

ISSN:0048-6604    

DOI:10.1029/RS008i008p00727

年代:1973

数据来源: WILEY

摘要:

A temporary phase recovery observed on long‐distance VLF propagation paths at sunrise is shown to be associated with cosmic‐ray ionization. Simultaneous measurements of the phase carried out at Atibaia, Säo Paulo, and Jaguaräo, Rio Grande de SuI, appear to demonstrate a latitudinal effect in this pheno

ISSN:0048-6604    

DOI:10.1029/RS008i008p00733

年代:1973

数据来源: WILEY

摘要:

Using a formulation based on Hamilton's ray equations, the variations of the path of a ray, and of the corresponding phase path, due to changes in the ray end points or the medium properties, are investigated. General expressions are obtained which represent the variations in terms of the solution of systems of ordinary differential equations. These may be integrated along the unvaried rays in order to evaluate the variations. The results, which may be applied to the analysis of a number of propagation problems, represent a simplification for anisotropic media and are also particularly well adapted to numerical applications.

ISSN:0048-6604    

DOI:10.1029/RS008i008p00737

年代:1973

数据来源: WILEY

摘要:

The frequency spectrum of a CW HF radio signal transmitted from an aircraft and propagated over a 1‐hop path inside the polar cap was recorded for about 50 nighttime hr during August 1967. Two different general types of disturbance were observed in these records: (a) a diffuse spectral broadening which was always present to some extent, even under quiet conditions, but which on some occasions was increased by as much as a factor of 2; and (b) discrete frequency anomalies, which were recorded at a rate of about two per hour, and which generally appeared above the carrier frequency (about 9 MHz) and decreased in frequency with a median slope of —2.2 Hz min−1. These discrete anomalies can be interpreted most satisfactorily in terms of Doppler‐shifted reflections from moving ionospheric irregularities. On the basis of this interpretation, the observations are taken to show that irregularity velocities are often in the range from 0.5 to 1.0 km sec−1, with a preferred direction of motion roughly toward the quadrant from geographic E to S and centered on geomagnetic E. However, the measurements were relatively insensitive to geomagnetic N‐S movements and to low

ISSN:0048-6604    

DOI:10.1029/RS008i008p00745

年代:1973

数据来源: WILEY

摘要:

The differential cross sections for an ellipsoid and elliptic cylinders having Gaussian electron‐density distributions have been obtained by a ray‐tracing procedure. Calculations for the case of an external magnetic field were restricted to the ellipsoidal distribution. The results show that the scattering is extremely sensitive to the orientation of the body. A peak in cross section occurs at the scattering angle corresponding to the ray normal to the critical surface, and increases as the surface becomes flatter. The cross section is sensitive to the ratio of peak density to critical density for moderate values but becomes relatively insensitive when the ratio exceeds 3. The total cross section (shown only for the elliptic cylinder) is a very sensitive function of both orientation and ratio of major to minor axes. The introduction of a magnetic field decreases the ordinary ray cross section; the extraordinary ray exhibits higher cross‐sectional values than the nonmagnetic field case. Comparison of the Gaussian ellipsoid with the corresponding conducting ellipsoid shows that the Gaussian has a larger cross section in the forward region but considerably lower values in the back‐scatter

ISSN:0048-6604    

DOI:10.1029/RS008i008p00753

年代:1973

数据来源: WILEY

摘要:

A study is made of the physics of radiation into the guide between the earth and the ionosphere from a center‐fed antenna consisting of a long horizontal wire grounded at its two ends. The length of the wire and the heighthof the ionosphere are short compared with the free‐space wavelength λ0. The antenna wire, together with its return path through the ground, constitutes the primary circuit of a transformer of which the ionosphere above the antenna to a distance of the order of λ0/2π is a part of the secondary circuit. This portion of the ionosphere, together with the corresponding portion of the ground, constitutes the secondary circuit of the transformer. This circuit applies voltage between the rest of the ionosphere and the rest of the ground, thereby launching a wave that propagates between the earth and the ionosphere towards the antipode. The coefficients of mutual and self‐impedance for the transformer are calculated and are used to relate the voltage at the terminals of the antenna to the wave that leaves the transformer for the antipode. The transformer action increases the radiated power by a factor of λ0/4habove that for the same antenna in the absence of the i

ISSN:0048-6604    

DOI:10.1029/RS008i008p00757

年代:1973

数据来源: WILEY

摘要:

This paper describes the hydrogen‐line interferometer system at the National Radio Astronomy Observatory. The system consists of telescopes, receivers, a data acquisition program, and a reduction program. The reduction program uses a random‐access data base which stores both the interferometer data and the synthesized maps. The calibration, mapping, and display of the data are described in de

ISSN:0048-6604    

DOI:10.1029/RS008i008p00763

年代:1973

数据来源: WILEY

摘要:

Various digital techniques for estimating the autocorrelation function of a signal are analyzed, with emphasis on methods applicable to radio‐astronomy and incoherent‐scatter studies of the ionosphere. The importance of coarse (one‐ or two‐bit) quantization is stressed, as is the effect of oversampling, the use of a sampling interval less than the inverse of twice the signal bandwidth. For applications such as incoherent scatter in which the signal strength varies with range (i.e., time), multibit by one‐bit multiplication combined with oversampling is probably the optimum strategy, although it requires 32% more integration time than the full multibit by multibit technique. For very high speed sampling of a signal of which the mean amplitude is constant, a three‐level by three‐level technique offers many advantages. It is nearly as simple to implement as conventional one‐bit correlation but requires considerably less integration time to achieve equal statistical accuracy (only 26% more than full multibit correlation, when sampled at twice the Nyquist rate, as compared to 146% for a one‐bit correlator with sampling at only

ISSN:0048-6604    

DOI:10.1029/RS008i008p00775

年代:1973

数据来源: WILEY

摘要:

The Rayleigh hypothesis is reviewed in relation to scattering by periodic surfaces, aperiodic surfaces, and bounded, two‐dimensional bodies. Conditions for its validity are described, and explicit results are quoted for a sinusoidal grating. Some methods to solve scattering problems for periodic surfaces are outlined. One particular procedure for periodic surfaces and bounded scatterers is examined in detail. This involves an expansion for the scattered field in terms of the same sets of elementary wavefunctions that occur in connection with the Rayleigh hypothesis. The coefficients are determined by satisfying the boundary condition in the least‐squares sense. It is shown that this solution converges uniformly to the scattered field at all points exterior to the boundary of the scatterer. Necessary completeness properties of the sets of wavefunctions are established in the appendi

ISSN:0048-6604    

DOI:10.1029/RS008i008p00785

年代:1973

数据来源: WILEY

摘要:

The integral equation of Hallen's type is derived in the time domain. The solution of the integral equation is carried out numerically, and the electromagnetic behavior of linear antennas and scatterers under various excitations is presented. The integral equation may be used to obtain time‐domain responses of coupled parallel linear antennas, and scatterers with loads. Combining with the method of characteristics in solving transmission line problems, the integral‐equation formulation is applied to the cases in which antennas and scatterers are connected to transmission li

ISSN:0048-6604    

DOI:10.1029/RS008i008p00797

年代:1973

数据来源: WILEY