An investigation of acoustic sampling effect on bedload velocity measurement by comparing ADCP bottom track to bi-static ADVP.

For the first time, the tracking mode of a mono-static acoustic Doppler current profiler (ADCP) for bedload evaluation is compared with a bi-static acoustic Doppler velocity profiler (ADVP) measurements close to the bottom, under controlled conditions in a laboratory flume with a loose sand bed. The high-resolution profiling achieved with the bi-static configuration of the ADVP is a step-forward compared with the monostatic ADCP configuration. The comparison shows that the ADCP underestimated the true bedload velocity, although the ADVP velocity, measured at the cells right above the immobile sediment bed, matched the apparent velocity estimated from the ADCP data. This underestimation is attributed to an uneven acoustic sampling of the ADCP. The return signal from moving particles is deteriorated by the strong intensity returning from immobile bedload layer beneath. This effect is not present in the bi-static profiling of the ADVP, which was able to distinguish the bedload velocities from the immobile bed to the top of the active layer. The ADVP-measured velocities at the top of the bedload layer resulted in the same range of velocity estimated by imagery data obtained in the same flume and for the same conditions.     «

For the first time, the tracking mode of a mono-static acoustic Doppler current profiler (ADCP) for bedload evaluation is compared with a bi-static acoustic Doppler velocity profiler (ADVP) measurements close to the bottom, under controlled conditions in a laboratory flume with a loose sand bed. The high-resolution profiling achieved with the bi-static configuration of the ADVP is a step-forward compared with the monostatic ADCP configuration. The comparison shows that the ADCP underestimated th...     »