Benthic lander systems' architecture and a new method for tracking deep-ocean fishes
Deep-ocean (benthic) landers are free-falling vehicles that are deployed from a ship and descend to the ocean floor by virtue of attached ballast. They carry with them scientific instrumentation to carry out in-situ experiments, and once operation is complete, an acoustic command from the surface vessel causes the lander to release its ballast and allow buoyancy to return it to the surface for recovery. Landers function autonomously, typically under the control of a central micro-controller and data-logger. The extreme environment in which landers operate require that all electronics is contained in special pressure housings and interconnection between modules is made using expensive deep-ocean cables and connectors. This thesis presents the concept of a new Controller Area Network (CAN)-based architecture, and a report is given of the development of a miniature network interface board suitable for use on benthic landers. One application of lander technology is in tracking the movements of abyssal fishes that forage close above the ocean floor. Small acoustic transponders are wrapped in bait and attached to the ballast of the lander. Scavenging fish attracted to the bait consume the transponders, after which a sonar system on the vehicle can track their movements. A new method for tracking these fishes is presented that uses a short-baseline hydrophone array mounted on a specially designed lander, AUDOS II. With no moving parts, this method has many advantages over previous systems that relied on scanning directional sonar. Tracking resolution has been greatly improved, and new software tools allow the movements of tracked fish to be viewed quickly and with ease.