An Evaluation of Acoustic Doppler Velocimeters as Sensors to Obtain the Concentration of Suspended Mass in Water

During the last two decades, acoustic Doppler velocimeters (ADVs) and other acoustic sensors have been used by researchers in the ocean science community to acquire information on current velocity and turbulence. More recently, acoustic backscatter systems (ABS) and acoustic Doppler current profilers (ADCPs) have been investigated for their use in determining sediment concentrations and particle sizes. Acoustic systems tend to be less prone to biofouling than optical turbidity sensors, and the high-frequency velocity measurements allow for a direct estimation of turbulence by the flux of particulate materials. This work investigates the responses of two commercially available ADVs to changes in mass concentrations of particles. A careful laboratory characterization of each sensor’s response to concentrations of three different size classes of polymer beads is evaluated and compared with the predicted response from acoustic scattering theory. Within uncertainties, experimental results are shown to agree with theory and these results demonstrate that, if the basic acoustic properties of the scatterers are known or if a local, vicarious calibration is performed, then ADV-type sensors can provide a robust estimate of particle concentrations from the measured acoustic return.