Characterization of Diffusive Noise Fields Using Ambient Noise Interferometry, Spatial Gradients and Acoustic Bright Spots

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.