Cross-spectral analysis of spaced-receiver measurements

The apparent velocity calculated by the dispersion analysis is interpreted in terms of the fundamental parameters of the cross-correlation analysis of spaced-receiver data, without any assumptions in addition to those already present in the latter technique. The dispersion analysis is then generalized, by assuming a realistic (power law) functional form for the power spectral density of the irregularities in the ionospheric F region. Next, an algorithm is proposed to estimate the anisotropy and the true drift velocity of the ground diffraction pattern directly from the cross spectra of the received signals. This technique is applied to HiLat spaced-receiver data recorded at Troms⊘, Norway (69.7°N, 18.9°N), in two different modes. In the first, it is applied on a relatively broad frequency band and its results compared with those from the cross-correlation analysis. A good general agreement is found. In the second mode, the technique is repeatedly applied on narrow and adjacent frequency bands, to detect possible frequency variations of the anisotropy of the diffraction pattern. A behavior analogous to that of the apparent velocity, previously reported in the literature, is then observed.