Cross‐correlation analysis and interpretation of spaced‐receiver measurements

Two algorithms which provide a statistical treatment to the estimation of the parameters of the cross‐correlation analysis of spaced‐receiver data are reviewed. Their results are compared using signals: (1) transmitted by a quasi‐stationary polar beacon and received at Goose Bay, Labrador (53.3°N, 60.3°W); and (2) transmitted by the orbiting Hilat satellite and received at Tromsø, Norway (69.7°N, 18.9°E). A good general agreement is displayed in this comparison. The former experiment indicates the possibility of extreme daily variations in the anisotropy of the ground diffraction pattern and in the true drift velocity of the in situ irregularities. The latter experiment displays geometrical enhancements in the intensity scintillation index S 4 , in the rms phase fluctuation σ ϕ and in the axial ratio of the ellipse which characterizes the anisotropy of the ground diffraction pattern, around the region of local L shell alignment of the ray paths. Increases of these parameters also are observed northward of Tromsø. These observations are thus consistent with a morphological model for anisotropy of high‐latitude nighttime F region irregularities proposed in the literature. Next, a possible dependence of the results of the spaced‐receiver measurements on the receiver baselines is discussed. It is argued that this mechanism could be responsible for the relatively small values of the anisotropy of the diffraction pattern obtained from the Hilat measurements at Tromsø. Finally, a procedure which combines a simple propagation model of the spaced‐receiver experiment with a nonlinear minimization algorithm is proposed to estimate the anisotropy of the in situ irregularities from that of the diffraction pattern.