Field testing of a new ADCP

Abstract

Since its introduction in 1992, the Teledyne RDI Instruments (TRDI) Workhorse ADCP has become ubiquitous, with literally thousands of systems deployed in nearly every body of water on earth. While the measurement itself remains relatively unchanged, in the intervening years the use of the measurements has changed to an extraordinary extent. Originally a novel way to measure currents sorely in need of proving and acceptance by the research community, ADCP measurements are now the tie facto standard for current measurement. What began as a useful tool for academic research continues in that role, but has also become standard equipment for real time decision making. ADCPs are now routinely used to measure river discharge and to aid flood control engineers in managing river levels. Since a terrible accident occurred in Tampa Bay, ADCPs now provide current information in near real-time to the pilots and captains of large vessels as they ply many of the world's major ports and waterways. Because offshore platforms cannot safely operate in the large currents of the Gulf of Mexico's Loop Current and the Eddies it generates, ADCPs play a critical role on all offshore platforms in the deep Gulf of Mexico. The presence and trajectories of these high Gulf of Mexico currents are forecast with great accuracy, the ADCPs real utility comes in determining when they are no longer affecting the rig. ADCPs provide information on an hourly basis in near real time from the TAO/TRITON array for climate forecasting. Returned Signal Strength Intensity data, originally provided strictly as an ancillary quality control parameter, has developed into a useful tool for studies as diverse as the diel migration of zooplankton to aid in creating optimal harbor designs based on sediment transport patterns in the area. The way that ADCPs are deployed has also changed dramatically. Originally a speed log for large vessels, the ADCP first morphed to a large, and very heavy, instrument for autonomous deployments on moorings. It has grown smaller and lighter over the years, with some ADCPs now easily hand carried from location to location for spot measurements. ADCPs are now available in horizontal configurations, with multiple beams, even as single point current meters. Perhaps most dramatic of all is the change in the typical user of ADCP data. The original early adopters of ADCP technology were members of the academic community well versed in marine engineering, computer programming and underwater acoustics in addition to their "main" interest of measuring ocean currents. Those users are still around of course, but they are now the minority. The typical user of today has less interest in how the measurement was made than in the robustness, accuracy and general utility of the current measurement for their purpose at hand. That is, the instrument is a given, the information it provides is what is needed. Many users are now no longer nearly as familiar with DOS and Unix (if at all) as they are with smart phones and touch screens. TRDI has been developing a new ADCP with these changes in mind. A prototype of the new system was deployed along with a Workhorse used as a standard for comparison. We present the results of that deployment, and some of the changes made in light of the changing requirements of the users.