The ef?cacy of sound to penetrate the seas made acoustic systems in the past c- tury the leading tools for sensing objects in and measuring properties of the seas. For over sixty years The United States Of?ce of Naval Research (ONR) has been a major sponsor of undersea research and development at universities, national laboratories, and industrial organizations. Appropriately ONR is the sponsor of this monograph series. The intent of the series is to summarize recent accomplishments in, and to outline perspectives for, underwater acoustics in speci?c ?elds of research. The general ?eld has...