VLF SOURCE LOCALIZATION WITH A FREELY DRIFTING ACOUSTIC SENSOR ARRAY

Source localization and tracking capability of the freely drifting Swa llow float volumetric array is demonstrated with matched-field process ing (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 dif ficulties in estimating the source depth and-range while the source az imuth estimate was quite successful. The main cause of the MFP perform ance degradation was incomplete knowledge of the environment. An envir onment adaptation technique using a global optimization algorithm was developed to alleviate the environmental mismatch problem. With limite d knowledge of the environment and a known location of the 14-Hz sourc e during a selected time interval according to the source log, the oce an-acoustic environment can be adapted to the acoustic data in a match ed-field sense. Using the adapted environment, the 14-Hz source was su ccessfully localized and tracked in azimuth and range within a region of interest using the MFP technique at a later time interval. Two type s of environmental parameters were considered, i.e., sound speed and m odal wave number. While both approaches yield similar results, the mod al wave number adaptation implementation is more computationally effic ient.