Current monitoring for environmental pollution studies by acoustic Doppler current profiling

Abstract

NOAA’s National Ocean Service (NOS) has been measuring and predicting coastal currents for over 100 years. In earlier times, measurements were made with current poles, or propeller-type current meters. In the late 1980’s, acoustic Doppler current profilers (ADCPs) were widely adopted. In Tampa Bay, 10 ADCPs (RD Instruments) were deployed in bottom-mounted platforms; a towed ADCP provided spatial contours of current speed. A real-time system provided 6-min averages of current to mariners and environmental managers. This system, still in place, provides vital information for tracking land cleanup of pollutant spills. Recently, an ADCP was added to a conventional current meter array deployed by NOAA/AOML at a wastewater outfall off Miami, Florida. The ADCP measurements compared well with earlier observations and facilitated assessing the effects of mooring motion and bio-fouling. Analysis of ADCP profile data revealed a near-linear velocity gradient from surface to bottom, enabling interpolation of velocity profiles from earlier measurements. ADCP backscatter intensity provided a rough estimate of suspended material. Future applications include mapping the three-dimensional circulation around point sources of pollution. Such maps provide environmental managers with data for effective effluent disposal management at minimum cost.