VLF SOURCE LOCALIZATION WITH A FREELY DRIFTING ACOUSTIC SENSOR ARRAY

Source localization and tracking capability of the freely drifting Swallow float volumetric array is demonstrated with matched-field processing (MFP) technique using the 14-Hz cw data collected during the 1989 Swallow float experiment conducted in the northeast Pacific by Marine Physical Laboratory. Initial MFP of the experimental data revealed difficulties in estimating the source depth and-range while the source azimuth estimate was quite successful. The main cause of the MFP performance degradation was incomplete knowledge of the environment. An environment adaptation technique using a global optimization algorithm was developed to alleviate the environmental mismatch problem. With limited knowledge of the environment and a known location of the 14-Hz source during a selected time interval according to the source log, the ocean-acoustic environment can be adapted to the acoustic data in a matched-field sense. Using the adapted environment, the 14-Hz source was successfully localized and tracked in azimuth and range within a region of interest using the MFP technique at a later time interval. Two types of environmental parameters were considered, i.e., sound speed and modal wave number. While both approaches yield similar results, the modal wave number adaptation implementation is more computationally efficient.