Characterization of Diffusive Noise Fields Using Ambient Noise Interferometry, Spatial Gradients and Acoustic Bright Spots Navy STTR FY2010.A Sol No.: Navy STTR FY2010.A Topic No.: N10A-T004 Topic Title: Characterization of Diffusive Noise Fields Using Ambient Noise Interferometry, Spatial Gradients and Acoustic Bright Spots Proposal No.: N10A-004-0723 Firm: Rocky Mountain Geophysics, Inc. 167 Piedra Loop Los Alamos, New Mexico 87544 Contact: Steven Taylor Phone: (505) 412-2841 Abstract: We propose to conduct a feasibility study for utilizing broadband sampling of the diffusive noise field in a dynamic environment. In ambient noise studies, the ability to resolve a wavefield is proportional to its time-bandwidth (TB) product. In a dynamic environment such as in the atmosphere or ocean, the nature of the impinging wave field is changing rapidly so that only short time segments can be used to model the ambient wave field thereby reducing the TB product. One way to counter the effect of a reduced time window is to increase the bandwidth of measurement. Our approach is to broaden the frequency spectrum used to characterize diffusive noise fields in dynamic environments by addition of Intensity Level Differences (ILD) caused by diffraction around a shadowing object to the more commonly used interferometric phase delay methods. Diffraction around a shadowing object can create acoustic bright spots that are easily detected. As an experimental test, we will use ambient noise data from existing infrasonic arrays and characterize the dynamic wavefield using passive interferometry and spatial gradiometry techniques. For spatial gradient techniques, the required sensor footprint is smaller and the wavefield can be mapped at higher resolution at closer ranges. Benefits: This work will benefit the Navy in that our proposed technique will be used to develop deployable sensor systems for characterization of diffusive noise fields in dynamic environments. Our proposed approach will lead to the development of a sensor system that has a small footprint and will be applicable for sound localization in proximity to submarines. The techniques will also be applicable to other settings where acoustic sound localization is required such as border security, facility perimeter monitoring, battlefield situational awareness among others and therefore has a number of commercial applications. Return