Abstract:

Ambient noise imaging at high frequencies (10--100 kHz) and over short ranges (10--100 m) has been successfully simulated in the past using conventional ray tracing, combined with a Helmholtz--Kirchhoff integral approach to evaluate scattering from relatively large targets. This worked well for the design of ADONIS, the first Acoustic Daylight camera, but lacked realistic diffraction and surface roughness effects which were thought to be important in some scenarios. Furthermore, data acquired using ADONIS and other coastal ambient noise measurements have indicated that more attention should be paid to snapping shrimp as sources in warm shallow water. These sources have a rich spatial and temporal statistical behavior which have been exploited in a new generation of imaging algorithms, and now designing a second-generation ambient noise imaging (ANI) system is possible. We have an improved simulation algorithm which has therefore been developed using Gaussian beams, to investigate the feasibility and performance of a second generation ANI camera. The new simulation includes diffractive corrections and rough surface effects. The results confirm that ANI cameras can be expected to work well in warm coastal environments out to distances of at least several hundred meters. The algorithm design and some simulations will be presented.