Modular autonomous array deployments using passive acoustic time synchronization

Abstract

Multi-element acoustic arrays generally use wired cable to transmit signals to a central recording location. While convenient, hardwiring hydrophones together increases array fragility and field costs while decreasing deployment flexibility. It is thus difficult to integrate acoustic array operations with field activities involving marine mammals in remote environments. Economic trends in the cell-phone and consumer electronics industries, combined with recent trends in tagging technology development, have led to the existence of compact low-power autonomous acoustic recorders that store data to either flash memory or small hard drives. In this presentation it is shown how two or more autonomous recorders can be time-synchronized using passive acoustic measurements of the background ambient noise field, effectively creating coherent array processing systems of varying aperture, spacing, and deployment geometry. Configurations tested to date include short and large-aperture vertical arrays off the coasts of Australia and Alaska, bottom-mounted horizontal arrays in San Ignacio Lagoon, Baja California, and instruments installed inside a glider. [Work sponsored by ONR Acoustic Entry Level Faculty Award.]