Use and Evolution of a Modular Digital Hydrophone Array

The Defence Research Establishment Atlantic (DREA) has been using and improving a linear hydrophone array since it was first reported at Oceans \´81. This array, which we call "Hydra", was developed primarily as a bottom-mounted array to collect acoustic information in continental shelf waters. It has been used in combined vertical and horizontal configurations in the waters off Nova Scotia, Newfoundland, Labrador, Baffin Island, Devon Island, and England over the past eight years. We have found that digitization and control of information right at the widely-spaced sensors in our system is invaluable in giving us the flexibility and accuracy required for our environmental acoustics research. The hydrophones for vertical array portions were completely re-designed to reduce low frequency self-noise. The battery cans were changed to an in-line design to overcome deployment problems. The improved array design is discussed in this paper, along with our experiences in using this type of array.