Mooring Motion Monitoring Acoustic Navigation System

A long path, low frequency, acoustic tomography experiment is being conducted in the North Atlantic by members of the Scripps Oceanographic Institute, Massachusettes Institute of Technology and Woods Hole Oceanographic Institution. Long, single-wire moorings are used to mount the necessary instrumentation. A high frequency acoustic navigation system monitors mooring motion to reduce degradation of the acoustic data by this source of error. The navigation system consists of a microprocessor controlled transceiver mounted at the top of the mooring and three recoverable transponders anchored on the bottom approximately one water depth away from the mooring anchor. At predetermined intervals, the transceiver simultaneously interrogates the three transponders and measures the round trip travel times. These data are recorded along with the time and date of the measurement on a small, single-track tape recorder. Each transponder is mounted within a self-buoyant glass housing and can be commanded to release for recovery. A 1.25 watt-second flash is also incorporated in the housing to aid in recovery. This paper describes the design of the transceiver and recoverable transponders and gives results from a short-term development.