Data telemetry for ocean bottom instrumentation

A data delivery system was developed for the Northern Gulf of Mexico Littoral Initiative that allows access to data from bottom mounted instrumentation. The system consists of two parts, a trawl resistant sub-surface component and a separate surface buoy. The sub-surface component employs a trawl resistant bottom mount containing an acoustic Doppler current profiler equipped with a Micro-Modem (μModem). The surface expression consists of a buoy equipped with an acoustic receiver (Utility Acoustic Modem, or UAM), a system controller and an Argos transmitter (PTT). The μModem acoustically telemeters data from the ADCP on an hourly schedule to the UAM on the nearby (~500 m) surface buoy. Data from the acoustic receiver are forwarded via the controller to the Argos transmitter. To maximize data throughput of the Argos link, the controller loads a circular buffer containing the most recent eight hours of data into the PTT each hour. These data are continuously transmitted until the next hourly update. The controller also performs resynchronization of the acoustic system in the event acoustic communications are lost. One particular benefit of this system is the ability to perform measurements in high traffic locations while maintaining the surface buoy at a safe distance from navigation aids. One system is currently deployed in a high traffic area, in Horn Island Pass, due south of Pascagoula, Mississippi. This paper describes the overall system and presents data from initial deployments