If electromagnetic radiations from ionospheric current systems are considered sources of micropulsations, it becomes instructive to examine the following model problem: What are the electric and magnetic fields in the vicinity of a plane, homogeneous earth due to a line current source above this model earth? As the micropulsation frequencies are quite low (order of 1 cps), the nearfield considerations become significant. The solution for this near field problem is presented and the fields at the earth's surface are evaluated for a set of parameter values chosen to approximate an ionospheric source at a typical micropulsation frequency.

Radio signals from artificial earth satellites propagated through the earth’s ionosphere are subjected to phase delay, refraction, and attenuation. These effects cause uncertainties in the determination of the vacuum Doppler shift of CW signals. To understand the nature of these ionospheric contributions to the Doppler shift, a theoretical expression for the refracted Doppler shift that is an inverse power series in terms of the frequency of the signal has been derived. A computer program has been written that uses ray theory in conjunction with a model ionosphere to evaluate each term of this expression. The nature of each term is discussed, and its relative importance is shown. The ionospheric contributions that are proportional to (1/ƒ) and (1/ƒ³), which result from phase delay and refraction, respectively, are the predominate terms; therefore the effects of refraction on a radio signal can be connected by using three‐frequency Doppler data. The ionospheric contribution that is proportional to (1/ƒ²) is insignificant. Three‐frequency Doppler data were recorded to evaluate the refraction effects in the refracted Doppler data. Two sets of experimental data are included that show the refraction effects.

The return of the ATS‐6 satellite to a western longitude during the fall of 1976 presented a unique opportunity to perform low‐angle‐of‐elevation measurements at 30 GHz. For this purpose a receiver using a 1.5 m antenna was set up at Port Aransas, Texas, resulting in a propagation path entirely over water. The 30 GHz beacon was monitored daily for at least one hour from 8 September to 21 September 1976. During the time the elevation angle changed from 1.5° to 17.3°, the mean attenuation decreased from 20 to 2 dB and the standard deviation from over 6 dB to less than .2 dB. The deep fades at angles below 4° show significantly sharper nulls than peaks on a log scale. Spectra of the log amplitude fluctuations vary as the (−8/3) power of the spectral frequency in the limit. A flattening is noticeable at the low frequencies. A precipitation event at 8.5° elevation produced a 16 dB fade and significantly increased the variance.

Summq-Refractiveindex variations in the atmosphere cause errors in radar measurements. This paper presents the results of a theoretical study of the elevation-angle error due to the refraction of electromagnetic waves in the troposphere. The study is based upon ray theory, using standard meteorological data reported by the United States Weather Bureau for the surface and the standard pressure levels. Computed errors are tabulated for thirty-four monthly mean refractive-index profiles selected as being representative of various type air masses for different seasons and latitudes. In order to get an indication of the spread in propagation errors to be expected during a particular season for ~e d locations, computations have been carried out based on the 03002 soundings for the odd days of January (1950)(1951)(1952)(1953)(1954) and July (1950-1953) for nine U. S. locations. The diurnal influence is investigated by analyzing the variations in surface refractive index for January and July, 1953, and also for nine U. S. locations. INTRODUCTIOK

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