A measurement system and analysis procedure for determining the spatial phase structure function of ionospherically reflected waves

A 40-km sparse high-frequency (HF) receiving array is described which was used to measure the instantaneous phase at eight sites within the array of a pulsed 9-MHz transmission from Boulder, CO, to the Philadelphia, PA, area. The experimental program was designed to produce data on the statistical properties of the phase-front of a wave after passage through the ionosphere for the purpose of assessing the design problems of an array large enough to focus a 1-km cross-section beam at transoceanic distance (array size the order of 100 km). The problem of the effect of phase-front fluctuations due to turbulence induced scattering and internal ionospheric waves is formulated. The adaptive beamforming and scanning program of the Valley Forge Research Center, University of Pennsylvania, Philadelphia, is expected to yield solutions to this problem through self-cohering procedures. The nature of the desired measurements and a measuring system for accomplishing the task are also described.