Time structure of bistatic reverberation in the long-range propagation of explosion-generated signals

In experiments on the long-range propagation of explosion-generated signals, a noise background accompanying the classical signal quartets are repeatedly observed. The background smoothly increases before the arrival of the first signal of the quartet, then decreases, and completely vanishes after the arrival of the last signal of the same quartet. The data of an experiment performed in winter in a deep-water region of the northwestern Pacific are considered. These data are used to demonstrate the phenomenon at hand and to show that the noise background of the quartets is the manifestation of the bistatic reverberation caused by sound scattering by the rough ocean surface towards the receiver located a long distance from the source. An easy-to-use technique is proposed for calculating the time relations between the direct signal and the surface-reverberation one. Calculations are performed for the time structure of the bistatic surface reverberation to explain the observed features of the phenomenon.