Acoustic daylight: Preliminary results from an ambient noise imaging system

A broadband (8–80 kHz) multibeam (126) acoustic daylight system has been developed which forms real‐time images at a 27‐Hz frame rate using only natural ambient noise in the ocean. The color and intensity of each pixel of the final image is determined by the spectral shading and intensity of the received signal in each beam normalized to a running‐average ambient noise spectrum. The first deployment of this system will be made from a floating research platform (ORB) during August in San Diego Bay. The high‐frequency ambient noise at this site is dominated not by surface waves, but by colonies of snapping shrimp (Alpheus and Synalpheus) associated with nearby structures and other habitats. The preliminary results from this deployment will be presented, including a description of the data processing and color mapping algorithm, the ambient noise environment, and some preliminary image results from simple targets at close range. [Work supported by ONR.]