default The ADCP as a proxy for suspended sediment concentration: calibration and comparison against optical data during an extended test in the Marine Protected Area of Portofino

By

The ADCP as a proxy for suspended sediment concentration: calibration and comparison against optical data during an extended test in the Marine Protected Area of Portofino. Bassetti, M. ; Grandi, V. ; Carta, A. ; Rixen, M. ; de Strobel, F. ; Gualdesi, L. ; Fioravanti, S. NURC-FR-2006-013. October 2006.

Transmissometer and backscatter devices are widely used to measure sediment concentration, but they provide only sparse temporal coverage and are therefore of limited use over longer periods. Acoustic backscatter measurement using an ADCP (Acoustic Doppler Current Profiler) is a non-intrusive technique for monitoring suspended sediment particles covering the whole water column. This technique offers the opportunity to remotely measure suspended loads with a temporal and spatial resolution that cannot be achieved by optical methods. The concept of using backscattered acoustic energy as a measure of the concentration of suspended matter has long been recognized, but only recently can this be done with any degree of reliability. A commercial software tool specifically designed for this task has been used to find a relationship between acoustic data and sediment information. This process is regarded as calibration and is generally carried out using either concentration values from water samples or turbidity data collected by optical sensors. The SEPTR (Shallow water Environmental Profiler in Trawl-safe Real-time), a platform with profiling and communication capabilities developed at NURC (NATO Undersea Research Centre), is the ideal workbench for the calibration of acoustic measurements since it contains ADCP and optical sensors that simultaneously measure the same water column. In July 2005 one unit was deployed in the Marine Protected Area of Portofino (Italy) where storm resuspension has been observed. This extended deployment provided data on backscattering, turbidity, fluorescence, temperature, salinity, solid concentration and chlorophyll from which ADCP calibration coefficients were used to infer suspended sediment material.