Some comparative directional measurements on short radio waves over different transmission paths

Observations on first-and second-order F-layer echoes from a pulsed transmitter at frequencies of 5¿8 Mc/s have been made at two direction-finders separated by 213 km. From a comparison of first-order bearings over the two paths it has been found that negligible correlation exists between similar components of the random ionospheric tilts at points separated by 106 km. However, relatively small average tilts over a period of an hour have been found to occur, and these are correlated over wide areas; they show a regular diurnal variation. The mid-points of the two transmission paths lay on land and on sea respectively, and a comparison of the directional variations exhibited by the second-order echo showed that the land behaved as a rougher reflector than the sea. The resulting difference in the total variance of bearings on this echo for the two paths was, however, small, as the deviations were mainly caused by ionospheric tilts.