Full Field Ambiguity Function Processing in a Complex Shallow-Water Environment

Abstract : For many acoustic environments, the power in a target's acoustic field incident on a linear array segment is concentrated in horizontal angle but distributed over a significant vertical angle. For these environments, both signal-to-noise ratio (S/N) gains and range, bearing, and depth estimates may be possible from an ambiguity surface processor obtained as a spatial correlation using a replica of the signal field in the three unknown source location parameters. This report presents an initial evaluation of an ambiguity surface processor for the Pekeris acoustic environment. Results for a vertical array segment indicate high-quality estimates of both range and depth. For a segment with horizontal extent and for known source depth, the sharp main peak of the ambiguity surface also supports the high quality estimates of source range and bearing, although for small array tilt angles, the quality of the range estimate is limited by the prevailing S/N because of the presence of extraneous sidelobe peaks. Increasing the tilt angle significantly reduces the level of the sidelobe peaks. Furthermore, the ambiguity surface processor achieves gain enhancements up to 2 dB using a purely horizontal array, and in excess of 20 dB using the vertical array.