A Spar Buoy Oceanographic Telemetry System

Abstract

The Brookhaven National Laboratory has been deploying a Spar Buoy Oceanographic Telemetry System (SBOTS) since 1976. During much of this period the system has undergone modification in its initial design, which has now evolved to an accurate and reliable form of real time oceanographic data acquisition. The design and operation of SBOTS is described in this communique. The SBOTS is comprised of buoyant segments of PVC pipe, stainless steel instrumentation cages, a surface antennae, and a power supply as an anchor. The segments are joined with a patented 'J' lock connection that allows only tilt but no vertical or azimuthal movement. Electrical cable segments are secured externally and are joined with underwater connectors. The standard sensor package includes an electromagnetic current meter, a conductivity sensor, and two thermistors. The full SBOTS typically will be equipped with four of these standard sensors, a pressure sensor, a compass/tilt sensor, and a processor. Most of the sensor outputs are in volts (0-5) which the processor averages, and then converts to frequency for transmission. The receiving station is at Brookhaven's 175 m tower and includes a dedicated PDP 11/40 computer. The data block is transmitted (218 MHz) 128 times bit and frame synchronously at a bit rate of 32 kHz, and is recorded on 9 track 800 bpi ASC 11 tape. The deployment of the SBOTS is limited to approximately 30 n. miles line-of-sight range from the Brookhaven receiving tower. Deployments have been made in water depths of 20-40 m on the shelf off Long Island. The SBOTS are assembled in the well deck of a LCU and are launched antenna first off the stern ramp. Recovery is made in reverse via an acoustic release connection to a battery/anchor lift line. Pre- and post-system calibrations are conducted on individual sensors via the processor, transmitter, receiver, and data recorder.