LABORATORY MEASUREMENTS OF CURRENT FLOW USING CROSS-CORRELATION ON ACOUSTIC BACKSCATTERING FROM SUSPENDED SEDIMENTS

The application of acoustic backscattering, for measuring near-bed hig h-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, similarl y detailed flow observations would be advantageous. In the present wor k backscattering from suspensions of marine sediments has been investi gated to examine the potential of using the backscattered signal to al so measure high-resolution near-bed vertical profiles of horizontal cu rrent flow. The approach adopted has been to attempt to utilize the te mporal coherence in the suspension field, and to employ cross correlat ion of the backscattered signal between pairs of horizontally separate d transducers to measure current profiles. To investigate this techniq ue a series of laboratory measurements have been conducted for a varie ty of experimental arrangements, and the outcome from these measuremen ts is reported in the present work. An examination of the suspension h eld has been conducted, and cross correlations between pairs of transd ucers investigated. Using cross-correlation time lags, current profile s have been calculated, and the results assessed using laser Doppler f low measurements. Comparison of the acoustic cross-correlation flow me asurements with the Doppler reference measurements show a high degree of agreement, and strongly support the use of the cross-correlation ap proach to accurately measure vertical profiles of the mean horizontal current. (C) 1988 Acoustical Society of America. [S0001-4966(98)00309- 9].