High-frequency radar ground clutter spatial correlation analysis: Transverse ionospheric drift velocity

A method of evaluating transverse ionospheric winds from oblique high-frequency radar ground scatter is presented. Measurements of the two-point, two-time mutual coherence function (MCF) of ground clutter targets made by the Kodiak Super Dual Auroral Radar Network (SuperDARN) HF-phased array radar illustrate that the spatial distribution of the backscattered electric field moves coherently across the radar aperture over time. Diffraction theory is applied to illustrate that the observations are consistent with an ionospheric drift transverse to the look direction of the radar. A general theoretical expression for the MCF is derived whose amplitude contours in the space-time plane may be simply related to the azimuth angular spectrum and Doppler spectrum of the incident signal and a transverse ionospheric drift between the radar and the illuminated area. A method of estimating ionospheric drift from the observed MCF is developed and applied to observations made by the Kodiak SuperDARN radar.