Amplitude characteristics of back-echo signals on extra-long-range paths of differing orientation

During February-March 1975, experiments were performed in which a research vessel, sailing from the Indian Ocean across the Atlantic Ocean to the shores of South America, received echo signals at different orientations from two transmitters (at 10 and 15 MHz) in Siberia. Changes in maximum diurnal amplitudes of direct and echo signals are studied as a function of length and orientation of the path. For the direct signals, the maximum diurnal amplitude depended primarily on the length of the path; for echo signals it was dependent on path length as well as on inclination of the path to the equatorial plane. The mean effective reference attenuation for different paths is computed from values of maximum diurnal amplitude.