The physical significance of the correlation ellipse in ionospheric drift analysis

It is shown that the correlation ellipse bears no relationship to the “average” shape of irregularities in the amplitude pattern formed at the ground from the interference of radio waves reflected or scattered from the ionosphere. The concept that the correlation ellipse should be related to the average shape arose because it was considered that the cross‐correlation coefficient for zero delay between two fading records (with spatial separation r) was related to the average normalized amplitude of the irregularities at a displacement r from the center of the average irregularity. As shown in this paper, the cross‐correlation coefficient for zero delay depends only on the mean fading period and the mean and variance of the time delays between corresponding fades. It retains its usual significance only if r is in the direction of drift.