Some Perspectives and Recent Findings in Shallow Water Acoustics

Shallow water acoustics has had in this country a long, though sporadic, history dating back to World War II, when the acoustic mine stimulated feverish activity in the subject. Yet, in spite of the impressive body of theory, model studies, and field data that has accumulated in subsequent years, many aspects of this most difficult branch of underwater acoustics are not understood. Many of its complications are due to the temporal and spatial variability of the shallow water medium and its boundaries. For example, we have found the transmission of shallow water sound to vary with direction and time at one location and to be different at apparently similar locations. Such variations make acoustic prediction difficult, and necessitate on-the-spot measurements at the place and time that data is required. To this end, we have developed and tried out at a number of coastal locations an airborne method of data collection using sonobuoys, explosive sound signals, and simple, portable recording equipment. The transmission results have been summarized by loss contour charts showing the transmission environment around a receiving point in shallow water.