Spatial Horizontal Coherence of Acoustical Signals in Shallow Water,
SACLANT ASW RESEARCH CENTRE LA SPEZIA (ITALY)
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The cross-correlation function of a acoustic signal between various pairs of hydrophones on a horizontal array gives an estimate for the spatial coherence function. The width of this function is defined as coherence length. Its reciprocal value is a measure of the angular uncertainty of the array caused by the transmitting medium and its boundaries. The relationship between this value and the angular scattering function and its implication on array performance is discussed. Experiments have been performed in two shallow-water areas north and southeast of the island of Elba in both summer and winter conditions, using broadband acoustic sources of 180 g TNT explosive launched at different ranges. The broadband data were analyzed for different frequency bands to obtain the angular uncertainty as a function of range. During summer a higher angular uncertainty was found than under isothermal winter conditions but it was still less than one degree for ranges between 200 m and 20 km. The results are compared with data reported in the literature for the great Fisher Bank in the North Sea and for the Gulf of Lions.
- Acoustic Detection and Detectors