Localizing swimming objects in noisy environments by applying nearfield acoustic holography and minimum energy method

A problem in localizing individual swimming objects acoustically is the high amount of strongly fluctuating ambient noise due to turbulent pressure fluctuations, thermal and seismic noise, motoring vessels, wind and marine mammals. In littoral and other shallow waters additionally the complex boundaries produce absorption of high-frequency components and strong reverberation in other frequency regions, refraction due to sudden changes in temperature and scattering from the rough sea surface and floor. In this paper localization of a single swimming object in presence of disturbing sources and noise is simulated. Lowfrequency nearfield acoustic holography (NAH) based on vector hydrophone array measurements is combined with minimum energy method (MEM) to increase detection certainty. This combination of NAH and MEM appears to be a reliable and robust detection method suitable e.g. for sort-range navigation in littoral waters and for iceberg detection in open waters.