Fixed Path Acoustic Transmission in the Presence of Internal Waves

Publisher Website
Google Scholar
Abstract
Results from several sources have indicated that internal (thermal) waves might cause significant fluctuation in sound transmitted through the ocean. A series of experiments at sea was begun in September, 1959, to study direct evidence of sound field distortion produced by the internal waves. The experiment consisted of acoustic transmission of 0.2-msec pulses at 92 kcps over a horizontal range of 400 to 500 ft. The source was supported 50 ft from the bottom, being attached to a fixed stable platform; the hydrophone was supported 3 to 10 ft from the bottom on a tripod. Thermistors in the field and isotherm followers on the platform provide data to determine the position, direction, speed, and amplitude of the waves. The platform (an oceanographic tower) is located about one mile off the coast at San Diego, California, in 60 ft of water where the bottom is rippled sand. A large volume of data has been collected for comprehensive coverage of many different thermal situations. Analysis of part of the data has led to the following preliminary results: (1) internal waves are always accompanied by marked fluctuation in sound pressure; acoustic fluctuation, above normal and longer than the normal period, can be reasonably attributed to each internal wave that passed through the sound field; the fluctuation in acoustic level is about 10 db; (2) acoustic fluctuation is also present when the water is isothermal, but in this case the maximum to minimum variation is only about 4 db.

This publication has 0 references indexed in Scilit: