The interpretation of ionospheric radio drift measurements—VI. Angle-of-arrival and group path [echolocation] measurements from digitized ionospheric soundings: The group path vector

Abstract

Some interpretive procedures for high resolution ionospheric radio echo phase measurements at spaced antennas and spaced radio frequencies are described and applied. Graphical representations of the phase range and group range, both derived from phase measurements, are shown in forms which facilitate their interpretation in terms of the motions and changes occurring at and below the echo reflection level. A particular application of these results is in the estimation of the level at which fading is imposed on the reflected echo. A procedure is given for calculating the direction of arrival and group-path simultaneously (i.e. the group-path vector) of an ionospheric radio echo, from digitized recording of the complex amplitude at spaced receiving antennas and spaced frequencies. Use of four or more antennas and two or more frequencies, as in the ‘Kinesonde’, permits solution of the problem by least-squares; this yields in turn a test of the plane-wave assumption and a calculation of confidence limits on the results. Weighted phase differences between channel pairs are obtained by time-averaged complex crosscorrelation, thus increasing the accuracy of the analysis. Examples are given of applications in ionospheric diagnostics (particularly in defining the level at which fading is imposed) and in the tracking of discrete objects such as cesium ion clouds released from rockets. The procedure of correlation analysis employed previously in this series of papers to study ionospheric motions, is shown to give results consistent with the large-scale ion cloud motions deduced from echolocation calculations.