Explorations of in-situ source localization in the deep ocean using frequency difference matched field processing and matched autoproduct processing

Abstract

Matched field processing (MFP) is a well-known technique for source localization in challenging environments. MFP involves correlating array-recorded fields with calculated replica fields developed from knowledge of the acoustic environment. Incomplete knowledge of the environment causes mismatch between measured and calculated fields, and this mismatch can cause MFP to fail at relevant ranges and frequencies in the deep ocean. Given that the severity of this mismatch increases with frequency, a proposed remedy to the mismatch problem is to analyze the frequency-difference autoproduct of the recorded field, rather than the field itself. The phase of the frequency-difference autoproduct is expected to mimic that of an out-of-band field at a selectable below-band frequency, thereby mitigating the severity of the mismatch at in-band frequencies. This autoproduct is then matched either to a replica field at the below-band frequency, or to an appropriate calculated autoproduct field. This presentation explores these methods, and higher-order corrections, to localize moored sources using data from the North Pacific Acoustic Library. Localization statistics are presented based on the closest moored source, 130 km from the receiving array with a signal bandwidth from 200 to 300 Hz. [Sponsored by ONR.]