A Buoy System For Acquiring, Processing and Telemetering Real Time OCS Oceanographic Data
Authors: Lobecker Robert N. , Higley Paul D. , Cook David O. 
Published: October 2008

As part of a physical oceanography data collection program being sponsored by the U.S. Bureau of Land Management on the New England OCS, a moored buoy instrument system has been developed to measure various subsurface parameters. The parameters sensed include current speed, current direction, conductivity and temperature at different depths; and bottom pressure. Components of the mooring include: an anchor-power supply, sensor packages, a subsurface buoy housing a microprocessor, and telemetry transceiver, an oil-filled rubber hose serving as the strength member, and a surface-piercing mast surmounted by a telemetry antenna. This design minimizes stress on electrical wiring and provides a secure link through the air-water interface. Sensors being incorporated into the system include Marsh-McBirney electromagnetic current meters, Neil Brown fluxgate magnetometer compasses, ODEC conductivity probes, YSI thermistors, and Aanderaa pressure gauges. The microprocessor-based sampling scheme filters out short period phenomena and computes resolved NS-EW currents, salinities, and the cross-products of currents with temperature and salinity. Thirty minute data averages, along with electronic "housekeeping" parameters, are te1emetered to the GOES satellite using an interrogatab1e system and relayed to shore. Operational systems were deployed during the fall of 1977.

INTRODUCTION

In 1976, the U.S. Bureau of Land Management initiated a physical oceanographic study as part of the environmental studies program for the New England outer continental shelf. The Georges Bank region of the outer shelf had been delineated as a potential site of petroleum resources, the Bureau to prudently reconcile the existing fishery in this area with petroleum development. A threefold data collection program was launched to acquire information on surface currents, subsurface currents and associated parameters, and hydrography. The subsurface parameters, which were to be recorded with instrumented buoys, include current speed, current direction, conductivity, temperature, and bottom pressure. Calculations of salinity and the cross-products of current with salinity and temperature were desired, with all data expressed as 30-minute averages.

Several special conditions had to be satisfied in the design of an instrumented buoy system for the Georges Bank application. A sampling scheme with rapid data acquisition was required to enable resolution of short-period fluctuations caused by surface gravity and internal waves such that longer period transport would not be aliased. Instrument response times had to be commensurate with this sampling frequency. High accuracies were needed to resolve anticipated vertical variations in salinity and temperature, and particularly to compute cross-isobath transport since flow is primarily parallel to isobaths. Implementation of the sampling scheme and valid calculation of half-hour cross-product averages dictated the use of an in-situ microprocessor. Because previous investigators had suffered significant attrition of moored equipment due to conflicts with commercial fishing activity, telemetry was desirable to minimize data loss. The remote location of the study area suggested that sufficient power be provided to allow a quarterly service interval. Finally, the strong tidal currents, high waves, and frequent storms on Georges Bank required a strong, stable mooring with a reliable link through the air-sea interface.