Three‐dimensional localization of a blue whale using broadband matched‐field processing for range and depth, and plane‐wave adaptive beamforming for azimuth

Abstract

During a recent shallow water experiment conducted 10–15 km west of San Diego, blue whale calls were recorded simultaneously on two underwater hydrophone arrays, an 18‐element, 205‐m‐aperture horizontal line array, and a 64‐element, 115‐m‐aperture vertical line array. These data are used to localize the calling whale in 3‐D space and then to make estimates of its source level. First, adaptive plane‐wave beamforming is used with the horizontal line array data to obtain finely resolved bearing estimates. Then, the bottom bathymetry profiles along these bearing estimates are used as input to a 2‐D full‐wave‐field normal mode code (written by Mike Porter) for generating ‘‘replica vectors’’ (i.e., predictions of the acoustic field) received by the vertical line array. A search in range and depth for the best match between the replica vectors and the actual field measured by the vertical array (‘‘matched‐field processing’’) then is performed to obtain the best‐fit position of the whale in 3‐D space. Finally, estimates of the source level of the whale calls are made. [Work partially supported by ONR, Code 321.]