Scattering at oblique incidence from ionospheric irregularities(Abstract)

THE PURPOSE of this paper is to supply a review of the experimental investigations conducted by a research group at the National Bureau of Standards on the subject of oblique incidence ionospheric scatter at very high frequencies. Emphasis is placed on the results which contribute to further understanding of the behavior of the scattered signals and the physics of the ionosphere. The main topics discussed are long- and short-term characteristics of scattered signals. Included under the latter are the results of simultaneous observations at closely spaced receiving points. Next experimental techniques are discussed from which the heights of the ionospheric irregularities can be deduced and results of their use at different seasons and times of day are given. It is found that all the scatter which could be observed with the available techniques resulted from irregularities in the region of the ionosphere, and most of it came from the lower parts of the region. The following section deals with the dependence of the scattering on frequency; a range of frequencies from 27.775 mc to 107.8 mc is examined. The main part of the report concludes with the results of an experiment which gave information on the dependence of ionospheric scatter on the angle of scatter. A final section reviews the results of some simultaneous observations in Alaska dealing with the characteristics of ionospheric scattering in the auroral zone. This section emphasizes the different and new results from the Arctic.