The technique of ionospheric investigation using ground back-scatter

The skip distance in short-wave propagation is measured by observing the time delay of echoes scattered from the Earth´s surface beyond the skip distance. A theoretical study shows that the method should give good accuracy in determining skip distance, but cannot yield unique values of the height and critical frequency of an ionospheric layer at a distant point. The radar equation is used to find the intensity of back-scatter from the ground, and an approximate calculation indicates that the irregularities present on land and sea should be sufficient to explain the observed echo strength. The effect of ray focusing by the ionosphere is considered. Experimental results confirm the conclusions of other workers that the predominant sources of echoes are on the ground and not in the E region. An empirical correction for the effect of the Earth´s magnetic field shows that no error in the location of the sources is introduced by using no-field theory in the analysis of results.