Long range sound transmission : interim report no. 1, March 1, 1944 - January 20, 1945
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Experiments are described to demonstrate a new method of sonic signalling at extremely long ranges in the oceans, utilizing the natural sound channel. Signals were made by causing a four pound charge of TNT to explode at about 4000 feet depth. These signals have the following qualities: (a) Extremely long range transmission (probably 10,000 miles). (b) Signal is positively identifiable. (c) Abrupt termination of the signal allows the arrival time to be read with an accuracy better than l/20th second. This permits location of source to better than a mile, if the signal is received at three suitably located stations. (d) The signal duration is related in such a way to the distance that the distance may be estimated to 30 miles in 1000 from reception at a single station. The limitations are: (a) It is required that the great circle path which the sound follows between source and receiver lie entirely in deep water (probably at least 1000 fathoms). (b) Sound travels in water at a speed of roughly 1 mile per second so that the interval between the origin of the signal and its reception becomes sufficiently great to be a handicap for some uses, particularly with aircraft. The signals were received to distances up to 900 miles. Two receiving arrangements have been used, a hydrophone hung 4000 feet over the side of a ship which was hove to, and a shore connected. hydrophone which lay on bottom 4000 feet deep. Extrapolation of the results indicate a range of at least 10,000 miles from this size charge. Recommendation is made to utilize a network of monitoring stations to locate planes, ships, and life rafts in distress on the open oceans. Three or more stations receiving a signal could locate the source better than one mile.