Effects of Ocean Waves on Acoustic Signals to Very Deep Hydrophones

Abstract

Amplitude fluctuations of surface reflected signal pulses from a 1-kc source at a depth of 50 ft were recorded by two bottom-mounted hydrophones 500 ft apart and 2600 fathoms deep. Some features of the observations are attributed to ocean wave focusing effects. It is shown that the surface-reflected pulse amplitude distribution may be described by using a Rayleigh distribution for noise modified by adding a single-focused contribution of random phase. An observed delay in the envelope of the signal pulse amplitudes recorded by the two receivers that is greater than the wave-front delay is explained as resulting from the sweeping action of an acoustic caustic produced by the ocean waves. These effects should depend on the direction, wavelength, and speed of the ocean waves as well as on the orientation of the hydrophones and the source location. Auto- and cross-correlation functions were computed from the data. (This work was supported by the Office of Naval Research, U. S. Navy Department.)