Passive localization of acoustic sources in media with non-constant sound velocity
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There is a growing concern about the effects of low frequency sounds (LFS) on marine mammals. One way to assess these effects on marine mammals involves the study of disturbance reactions. Detailed research of disturbance reactions of submerged marine mammals requires 3-dimensional localization and tracking of the animals. An acoustic source is localized passively with the use of travel time differences (TTD) of a signal's reception received by multiple hydrophones at known positions. An initial approximation of source position is found using straight-line paths of sound propagation between source and receiver. An algorithm is then used to iteratively pinpoint source position in a medium with a non-constant sound speed. This algorithm calculates direct eigenrays connecting the approximate source position and each of the four buoys. These eigenrays are used to generate a set of TTD values that are subtracted from TTD values recorded in the field, giving TTD differences (TTDF). Ti = travel time to buoy i. TTDli=T,-Ti. TTDFi=TTD'li-TTDi. The depth coordinate of the source position is adjusted until TTDF3 = 0. Then one of the horizontal components of the source position is adjusted until TTDF, = +-TTDF2. Then the other horizontal component of the source position is adjusted until TTDF, = T-TTDF2. This process is repeated until TTDF3 = 0 after adjusting both horizontal components of the source position. Five hydrophone array configurations are tested, each with 30 pseudo-randomly generated source positions. Average errors of the 150 source position calculations, (x, y, depth) in meters, are (I︢.58, 1︢.70, 1︢0.44) for the straight-line, and (O︢.72, 0︢.83, 1︢. IO) for the algorithm. On average, the algorithm improves the source depth
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Includes bibliographical references: p. 38-40.
Issued also on microfiche from Lange Micrographics.
Brandes, Thomas Scott (1998). Passive localization of acoustic sources in media with non-constant sound velocity. Master's thesis, Texas A&M University. Available electronically from