Ocean Ambient Noise Studies for Improved Sonar Processing

Abstract

Abstract : The purpose of this research is to investigate multipath arrival structures that are present in received passive sonar data and exploit this for enhanced passive sonar detection and tracking capability. Inherent in passive sonar are several challenges that any effective system implementation must address. One of these challenges is how to best treat multipath arrivals. In some cases these can be a hindrance while in this research they are exploited. In certain environments, different arrivals (multipath and direct) retain significant coherence with respect to each other. This fact has been noted and exploited in recent decades with the development of the class of techniques known as matched field processing (MFP). While there has been a significant amount of academic focus on developing this approach in the context of the more established array processing methodologies, its practical adoption has been hampered due to the need for unrealistically accurate environmental models. Despite this shortfall, the conceptual basis of using multipath arrivals to enhance target localization still holds promise. In this project, the emphasis has been shifted to analytically and experimentally determining the true invariants in this problem context. Recent studies into localization of marine mammals have shown that with only rough environmental models, 3-D localization is possible using a single hydrophone [Tiemann, 2006]. The fundamental difference between approaches such as these and MFP is that while MFP attempts to predict exact phase differences between different arrivals, these approaches utilize the time differences of multipath arrivals (TDOMA), which are often far more stable. This concept has recently been extended to localization of small surface craft [See publication #2], and work is currently underway to apply it to underwater targets, both of which will be described in this report.