If you wish to read further on this topic, here are some suggest books and sites to check out:
Books:
1. MaCaulay, David, The Way Things Work, Houghton Mifflin Co., Boston, 1985.
2. Snyderman, Mary, Ocean Life, Publications International Ltd., Illinois, 1991.
Encyclopedias:
1. The Columbia Encyclopedia, 5th Edition, Columbia University Press, USA, 1993.
2. Colliers Encyclopedia, Lauren S. Bahr, P.F. Collier, New York, 1993.
3. McGraw-Hill Encyclopedia of Science and Technology, McGraw-Hill Book Co., New York, 1987.
Computer:
1. Salkever, Alex, Special to The Christian Science Monitor, Whales Vs. U.S. Defense?, May 5, 1998.
2. "Sonar", Microsoft Encarta, Funk and Wagnalls Corporation, 1994.
Internet:
1. http://www.sanjuan.edu/schools/arcade/SonarVA.html
2. http://www.beach-net.com/dolphins/communication.html
3. http://www.surfpac.navy.mil/EODC/eodmu3/3marmam.html
