Frequency and spatial correlations of fading radio echoes from the ionosphere

Abstract The cross correlation of the amplitudes of diffusely reflected fading ionospheric echoes on adjacent frequencies is analysed. The correlation function is measured experimentally for a number of frequency separations for E -, E s - and F -echoes. Simultaneous measurements are made of the cross correlation at closely spaced receivers. Comparison of the correlations on adjacent frequencies and at closely spaced receivers shows that the fading arises very close to the reflection level. The maximum value of the cross correlation function between echoes on adjacent frequencies is commonly displaced from zero time. This effect is interpreted as arising from apparent vertical motions of the ionosphere.