摘要:

Refraction effects cause radio waves travelling through the atmosphere to be bent. Without knowledge of the atmospheric parameters along the ray path, the degree of bending cannot be calculated deterministically. Since atmospheric emission at microwave wavelengths is dependent on temperature, pressure, and relative humidity, radiometric data contain information about these parameters. This study will make use of a Monte Carlo simulation of the atmosphere to demonstrate that atmospheric emission measurements can be used with surface refractivity to increase greatly the accuracy with which refractive bending can be estimated.

ISSN:0048-6604    

DOI:10.1029/RS008i010p00819

年代:1973

数据来源: WILEY

摘要:

Based on waveguide mode theory and a simple model to calculate the ionospheric reflection coefficient, electron density profiles are deduced from VLF data. A simplified day/night transition model is described. It is appropriate for explaining the mode conversion during sunset and sunrise and leads to conclusions concerning the change of the electron density profile within the transition region.

ISSN:0048-6604    

DOI:10.1029/RS008i010p00829

年代:1973

数据来源: WILEY

摘要:

A series of expressions to calculate the monthly medianF1layer penetration frequency (ƒoF1) as a function of the ionospheric indexIF2was reported byDuCharme et al., [1971]. Using similar techniques and the same data base, development of a series of expressions to calculateƒoF1as a function of the Zurich smoothed sunspot numberR12is described. The derived expressions are evaluated for the period of maximum solar activity 1967 through 1969 and compared with observedƒoF1data for this period, which are outside the 1954 through 1966 data base used to develop the expressio

ISSN:0048-6604    

DOI:10.1029/RS008i010p00837

年代:1973

数据来源: WILEY

摘要:

The optimum signal processing to follow a given radiometer front‐end is derived when it is desired to estimate, with smallest rms error, the temperature of a radio source. We find, for the important special case of small sources, that the optimum radiometer is implemented by the use of a compensating filter followed by square‐law detection and integration. We consider two examples of receiver front‐end gain characteristics, the Lorentzian and Gaussian shapes. Improvement over conventional radiometer performance is shown to be pos

ISSN:0048-6604    

DOI:10.1029/RS008i010p00841

年代:1973

数据来源: WILEY

摘要:

A log‐periodic array, three km in length, is operating at Clark Lake Radio Observatory. It makes one‐dimensional sweeps of the solar brightness distribution in the frequency range 20 to 65 MHz once per sec. The phasing of the array and the receiving system are described, as well as how the dynamic spectra are analyzed for the positions of solar radio sources. Simultaneous measurements at many frequencies enable the observer to remove the effects of ionospheric refraction and to obtain fundamental positions to an accuracy of about one arc min at decametric wavelengths. Fundamental positions are given for Cassiopei

ISSN:0048-6604    

DOI:10.1029/RS008i010p00845

年代:1973

数据来源: WILEY

摘要:

It is shown that in the above paper [Kostelnicek and Mittra,1971] and also in previous work [Mittra and Bates,1967], the solutions do not satisfy the edge condition due to an error in the asymptotic expansion of the infinite product employed in the solutions.

ISSN:0048-6604    

DOI:10.1029/RS008i010p00855

年代:1973

数据来源: WILEY

摘要:

HF radar signatures have been synthesized from a time‐dependent Gaussian ion cloud using a three‐dimensional ray‐tracing progam that can take into account both electron collisions and the earth's magnetic field. The ion cloud model is based on the theory of ambipolar diffusion and the model parameters are based upon the observations made during a barium cloud test conducted at White Sands, New Mexico. Ray‐tracing results have been generated for both ordinary (O) and extraordinary(X) modes as well as for the “no‐field” case. The results, presented in the form of a time‐history of the Doppler shift and the scattering cross section, are found to be quite similar for all three cases. Relative to theOmode, the X‐mode variations lag in time and obtain a maximum cross section which is greater only by about 2 db. The variations for the no‐field case fall in between that of theOandX, but closer to theOmode. The results show that the cloud is extremely defocussing with an estimated defocussing factor (relative to free space) for theXmode increasing from 7.6 × 103to 1.85 × 107over the interval 5 to 190 sec of cloud's life. The ray‐tracing signatures are compared to those synthesized by means of a hard expanding ellipsoid method with a view to evaluating the importance of underlying ionization. The effects are found to be such as to introduce a significant time lag in Doppler history and to cause a cross section reduction by a factor that builds up with time from 5 db to more than 30 db. A comparison drawn between the observed and the ray‐tracing signatures leads to the conclusion that good agreement between the two can be expected only when the clouds experience either slow or no deformation and st

ISSN:0048-6604    

DOI:10.1029/RS008i010p00857

年代:1973

数据来源: WILEY

摘要:

In this paper theH‐integral equation is investigated for the problem of plane‐wave diffraction by a thin plate. It is found that the limiting form of theH‐equation by itself is not complete unless the conditionis simultaneously enforced. By suitably combining the above‐mentioned equations, a new set of equations is derived for the two components of the surface current distribution on the plate. Several advantageous features of the new equations are pointed out, and numerical results based upon the use of these equations are presented for the thin‐strip and the square‐pla

ISSN:0048-6604    

DOI:10.1029/RS008i010p00869

年代:1973

数据来源: WILEY

摘要:

The characteristics of electromagnetic surface waves supported by a plane interface separating a semi‐infinite region of free space from another semi‐infinite region consisting of a double stream of plasma streaming parallel to the interface are investigated for the case in which the wave is progressing either in or opposite to the direction of the stream. The behavior of the surface wave is quite different from the case in which the plasma is stationary. For the case of waves progressing opposite to the direction of the streams, there are backward‐wave regions as well as regions of instability which occur below the plasma frequency. In the frequency range of instability, the surface wave undergoes traveling‐wave amplification in the direction of the streams. The wave amplification characteristics are examined and the dependence of each on the relative number density of the two streams as well as on the drift velocity is studied. It is found that the maximum amplification rate increases as the drift velocity is in

ISSN:0048-6604    

DOI:10.1029/RS008i010p00877

年代:1973

数据来源: WILEY