had three single ones), at 0.2 to 2.5 kilowatts. The simple type used 14.5 kHz magnetostrictive transducers at 0.25 kW, driven by capacitive discharge instead of oscillators, with range up to 2.5 km. The sonar's resolution is angular; objects further apart are imaged with lower resolutions than nearby ones. Another source lists ranges and resolutions vs frequencies for sidescan sonars. 30 kHz provides low resolution with range of 1000–6000 m, 100 kHz gives medium resolution at 500–1000 m, 300 kHz gives high resolution at 150–500 m, and 600 kHz gives high resolution at 75–150 m. Longer range sonars are more adversely affected by nonhomogenities of water. Some environments, typically shallow waters near the coasts, have complicated terrain with many features; higher frequencies become necessary there. See also Explanatory notes Citations General bibliography Hackmann, Willem. Seek & Strike: Sonar, Anti-submarine Warfare and the Royal Navy 1914–54. London: Her Majesty's Stationery Office, 1984. . Hackmann, Willem D. "Sonar Research and Naval Warfare 1914–1954: A Case Study of a Twentieth-Century Science" . Historical Studies in the Physical and Biological Sciences 16#1 (January 1986) 83–110. . Urick, R. J. (1983). Principles of Underwater Sound (3rd edition). Los Altos: Peninsula Publishing. . . Fisheries acoustics references Fisheries Acoustics Research (FAR) at the University of Washington NOAA Protocols for Fisheries Acoustics Surveys Acoustics Unpacked —A "how to" great reference for freshwater hydroacoustics for resource assessment "ACOUSTICS IN FISHERIES AND AQUATIC ECOLOGY" "Hydroacoustic Protocol – Lakes, Reservoirs and Lowland Rivers" (for fish assessment) Simmonds, E. John, and D. N. MacLennan. Fisheries Acoustics: Theory and Practice, second edition. Fish and aquatic resources series, 10. Oxford: Blackwell Science, 2003. . Further reading "Canada: Stable Sonics", Time, October 28, 1946. An interesting account of the 4,800 ASDIC sonar devices secretly manufactured at Casa Loma, Toronto, during World War II. Retrieved 25 Sept. 2009. "Radar of the Deep - SONAR", Popular Science, November 1945, pp. 84–87, 246, 250: one of the best general public articles on the subject External links FFI Facts: Sonars and the marine environment by the Norwegian Defence Research Establishment (FFI) Remote Sensing for Coastal Management: Single Beam Sonar—Coastal Services Center, National Oceanic and Atmospheric Administration 20th-century inventions Anti-submarine warfare British inventions French inventions Submarine warfare