You probably remember the old submarine movies when to find any vessels around them, they would send out a sound that sounded like a ping and then waited for the sound reflection to come back. That is what we are going to do. This should have a greater sensitivity (being all things are equal) than a traditional ping sensor.

Step 1: What's Needed.

Computer with working sound card and speakers
Working microphone attached tot he computer.

Software depending on the operating system.

http://stevetarzia.com/sonar/download.php

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Other downloads:

MSWindows:

http://eddiem.com/projects/chirp/download/

http://stevetarzia.com/sonar/SonarPM_0.8_installer.msi

Linux:

http://olea.org/paquetes-rpm/fedora-11/SonarPM-0.74-1.fc11.i586.rpm

Source for recompiling on Redhat:

http://olea.org/paquetes-rpm/fedora-11/SonarPM-0.74-1.fc11.src.rpm

Step 2: Bit of History.

Per Wikipedia:

Although some animals (dolphins and bats) have used sound for communication and object detection for millions of years, use by humans in the water is initially recorded by Leonardo Da Vinci in 1490: a tube inserted into the water was said to be used to detect vessels by placing an ear to the tube.^[1]

In the 19th century an underwater bell was used as an ancillary to lighthouses to provide warning of hazards.

The use of sound to 'echo locate' underwater in the same way as bats use sound for aerial navigation seems to have been prompted by the Titanic disaster of 1912. The world's first patent for an underwater echo ranging device was filed at the British Patent Office by English meteorologist Lewis Richardson a month after the sinking of the Titanic,^[2] and a German physicist Alexander Behm obtained a patent for an echo sounder in 1913.

ASDIC
In 1916, under the British Board of Invention and Research, Canadian physicist Robert William Boyle took on the active sound detection project with A B Wood, producing a prototype for testing in mid 1917. This work, for the Anti-Submarine Division of the British Naval Staff, was undertaken in utmost secrecy, and used quartz piezoelectric crystals to produce the world's first practical underwater active sound detection apparatus. To maintain secrecy no mention of sound experimentation or quartz was made - the word used to describe the early work ('supersonics') was changed to 'ASD'ics, and the quartz material to 'ASD'ivite: hence the British acronym ASDIC. In 1939, in response to a question from the Oxford English Dictionary, the Admiralty made up the story that it stood for 'Allied Submarine Detection Investigation Committee', and this is still widely believed, though no committee bearing this name has been found in the Admiralty archives.^[7]
By 1918, both France and Britain had built prototype active systems. The British tested their ASDIC on HMS Antrim in 1920, and started production in 1922. The 6th Destroyer Flotilla had ASDIC-equipped vessels in 1923. An anti-submarine school, HMS Osprey, and a training flotilla of four vessels were established on Portland in 1924. The US Sonar QB set arrived in 1931.
By the outbreak of World War II, the Royal Navy had five sets for different surface ship classes, and others for submarines, incorporated into a complete anti-submarine attack system. The effectiveness of early ASDIC was hamstrung by the use of the depth charge as an anti-submarine weapon. This required an attacking vessel to pass over a submerged contact before dropping charges over the stern, resulting in a loss of ASDIC contact in the moments leading up to attack. The hunter was effectively firing blind, during which time a submarine commander could take evasive action. This situation was remedied by using several ships cooperating and by the adoption of "ahead throwing weapons", such as Hedgehog and later Squid, which projected warheads at a target ahead of the attacker and thus still in ASDIC contact. Developments during the war resulted in British ASDIC sets which used several different shapes of beam, continuously covering blind spots. Later, acoustic torpedoes were used.
At the start of World War II, British ASDIC technology was transferred for free to the United States. Research on ASDIC and underwater sound was expanded in the UK and in the US. Many new types of military sound detection were developed. These included sonobuoys, first developed by the British in 1944 under the codenameHigh Tea, dipping/dunking sonar and mine detection sonar. This work formed the basis for post war developments related to countering the nuclear submarine. Work on sonar had also been carried out in the Axis countries, notably in Germany, which included countermeasures. At the end of World War II this German work was assimilated by Britain and the US. Sonars have continued to be developed by many countries, including Russia, for both military and civil uses. In recent years the major military development has been the increasing interest in low frequency active systems.
SONAR
During the 1930s American engineers developed their own underwater sound detection technology and important discoveries were made, such as thermoclines, that would help future development.^[8] After technical information was exchanged between the two countries during the Second World War, Americans began to use the term SONAR for their systems, coined as the equivalent of RADAR.

^Fahy, Frank (1998). Fundamentals of noise and vibration. John Gerard Walker. Taylor & Francis. pp. 375. ISBN 0419241809.
^ ^a ^bHill, M. N. (1962). Physical Oceanography. Allan R. Robinson. Harvard University Press. pp. 498.
^Seitz, Frederick (1999). The cosmic inventor: Reginald Aubrey Fessenden (1866-1932). 89. American Philosophical Society. pp. 41–46. ISBN 087169896X.
^Hendrick, Burton J. (August 1914). "Wireless Under The Water: A Remarkable Device That Enables A Ship's Captain To Determine The Exact Location Of Another Ship Even In The Densest Fog". The World's Work: A History of Our TimeXLIV (2): 431–434. http://books.google.com/?id=zegeQtMn9JsC&pg=PA431. Retrieved 2009-08-04.
^"Report of Captain J.H. Quinan of the U.S.R.C Miami on the Echo Fringe Method of Detecting Icebergs and Taking Continuous Soundings.". Hydrographic Office Bulletin (U.S. Coast and Geodetic Survey). 1914-05-13. (quoted in a NOAA transcript by Central Library staff April, 2002.
^The Rotary Bowcap
^ W Hackmann, Seek & Strike: Sonar, anti-submarine warfare and the Royal Navy 1914-54 (HMSO, London, 1984)
^Sonar