Shallow-Water Acoustics and Relevant Physics
Shallow-water Acoustics and Relevant Physics
By: Elizabeth Fortlage
Underwater Acoustics is a complex phenomenon. Leonardo da Vinci simplified the concept in 1940, two years before Columbus discovered America, by saying “If you can cause your ship to stop and place the head of a long tube in the water and place the outer extremity to your ear, you will hear ships at a great distance from you.” (5, p.2) There are many factors that contribute to the complexity of underwater acoustics and sonar. In the ocean things such as sound transmission losses in sea water, refraction phenomena, sound channels, influence of surface reflection on transmission loss, bottom reflection phenomena, source level, factors influencing echo levels, masking by noise, masking by reverberation, and acoustic outputs of ships all have to be taken accounted for (2). Shallow water is also usually a noisy environment because shipping lanes exist along coastlines. We are going to examine a few of these effects and see the direction that the developments in underwater acoustics may lead, as well as focusing on some military applications of sonar. We are going to start by looking at the history of underwater acoustics from a military standpoint to understand its purpose and realistic applications. The first quantitative measurement in underwater sound was in 1827 when Daniel Colladon and Charles Sturm collaborated to measure the velocity of sounds in Lake Geneva in Switzerland. By timing the interval between a flash of light and the striking of a bell underwater, they determined the velocity of sound to a surprising degree of accuracy.(5, p.2) By the turn of the century there was the first application for underwater sound, the submarine bell. By timing the interval between the sound of the bell and the sound of a simultaneously sent blast of a foghorn, a ship could determine its distance from the lightship where both were installed. The system was the momentum for the founding of
By: Elizabeth Fortlage
Underwater Acoustics is a complex phenomenon. Leonardo da Vinci simplified the concept in 1940, two years before Columbus discovered America, by saying “If you can cause your ship to stop and place the head of a long tube in the water and place the outer extremity to your ear, you will hear ships at a great distance from you.” (5, p.2) There are many factors that contribute to the complexity of underwater acoustics and sonar. In the ocean things such as sound transmission losses in sea water, refraction phenomena, sound channels, influence of surface reflection on transmission loss, bottom reflection phenomena, source level, factors influencing echo levels, masking by noise, masking by reverberation, and acoustic outputs of ships all have to be taken accounted for (2). Shallow water is also usually a noisy environment because shipping lanes exist along coastlines. We are going to examine a few of these effects and see the direction that the developments in underwater acoustics may lead, as well as focusing on some military applications of sonar. We are going to start by looking at the history of underwater acoustics from a military standpoint to understand its purpose and realistic applications. The first quantitative measurement in underwater sound was in 1827 when Daniel Colladon and Charles Sturm collaborated to measure the velocity of sounds in Lake Geneva in Switzerland. By timing the interval between a flash of light and the striking of a bell underwater, they determined the velocity of sound to a surprising degree of accuracy.(5, p.2) By the turn of the century there was the first application for underwater sound, the submarine bell. By timing the interval between the sound of the bell and the sound of a simultaneously sent blast of a foghorn, a ship could determine its distance from the lightship where both were installed. The system was the momentum for the founding of
References: 1. Katsnelson, Boris G., and Valery G. Petnikov. Shallow Water Acoustics. London: Springer, 2001. Print. 2. Kinsler, Lawrence E., and Austin R. Frey. Fundamentals of Acoustics. New York: Wiley, 1962. Print. 3. Kuperman, William A., and James F. Lynch. "Shallow-Water Acoustics." Physics Today 57.10 (2004): 55. Print. 4. Roscoe, Theodore, and R. G. Voge. United States Submarine Operations in World War II. Annapolis: United States Naval Institute, 1949. Print. 5. Urick, Robert J. Principles of Underwater Sound. New York: McGraw-Hill, 1975. Print. 6. Wright, M.C.M. Lecture Notes on the Mathematics of Acoustics. London: Imperial College, 2005. Print. I have neither given nor received, nor have I tolerated others’ use of unauthorized aid. Elizabeth Fortlage