Laboratory measurements of current flow using cross correlation on acoustic backscattering from suspended sediments

Abstract

The application of acoustic backscattering, for measuring near-bed high-resolution profiles of suspended sediment concentration and particle size, has advanced substantially in recent years. To interpret these suspension observations and link them with the hydrodynamics, similarly detailed flow observations would be advantageous. In the present work backscattering from suspensions of marine sediments has been investigated to examine the potential of using the backscattered signal to also measure high-resolution near-bed vertical profiles of horizontal current flow. The approach adopted has been to attempt to utilize the temporal coherence in the suspension field, and to employ cross correlation of the backscattered signal between pairs of horizontally separated transducers to measure current profiles. To investigate this technique a series of laboratory measurements have been conducted for a variety of experimental arrangements, and the outcome from these measurements is reported in the present work. An examination of the suspension field has been conducted, and cross correlations between pairs of transducers investigated. Using cross-correlation time lags, current profiles have been calculated, and the results assessed using laser Doppler flow measurements. Comparison of the acoustic cross-correlation flow measurements with the Doppler reference measurements show a high degree of agreement, and strongly support the use of the cross-correlation approach to accurately measure vertical profiles of the mean horizontal current.

Developments in acoustics for studying wave-driven boundary layer flow and sediment dynamics over rippled sand-beds

“…Given the multi-frequency capability of the BASSI the next step would to obtain 2DHV measurements of the suspended particle size as has been done with ABS in 1DV. Further, given the 2DHV ability, it may be possible to use cross-correlation of the backscattered signal between transducers and PIV type approaches on consecutive images of the suspended sediments to provide information on the flow field, (van Unen et al 1998, Best et al 2010.…”

Modeling analysis of ultrasonic attenuation and angular scattering measurements of suspended particles

“…One of the most established uses of ultrasound backscattering is the measurement of flow velocity and turbulence by tracking suspended particles, a method known as acoustical Doppler profiling (ADP). [15][16][17][18] There is a multitude of examples for the use of direct acoustical backscattering in marine geology or other civil engineering areas to measure suspended sediment concentration (SSC). [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] Backscattering measurements have the great advantage of having a very large penetration depth (several meters).…”