Some features of backscatter echo signal propagation

Observations taken on board the research ship Borovici (Feb.-March 1975) on the propagation of 10 and 15 MHz signals are described. The regular appearance of backscatter echo patterns on long signal hops is pointed out. A relationship between the period of passage of these signals and the angle of inclination of the propagation path to the plane of the equator is discerned. The optimum time of day for transmission of backscatter echo is at least partially dictated by the absorption minimum, which differs with the orientation of the propagation path. Conditions governing trapping into the return path and escape from same are also important, and nighttime electron concentration gradients may be important in the vicinity of the midlatitude dip.