Improving prediction of particle size with a novel acoustic bedload monitoring system consisting of phased microphone arrays and accelerometer

Abstract. Accurate measurement of bedload transport flux in rivers remains an important issue in hydraulic engineering. Acoustic-based devices provide a promising way to measure the transport rate with established calibration relationships between the signal and bedload particles. We develop a novel acoustic bedload monitoring system with phased microphone arrays (PMA) and accelerometer to localize the particle impact location and to better determine the particle size. Impact experiments with quartz spheres in a flume setting were performed to investigate the dynamic signal response of the PMA monitoring system for varying particle size and impact location. For a similar virtual set-up, the conventional beamforming method was used to determine the source characteristics of the acoustic wave on the scanning plane of the PMA structure. The model provides a calculation of the cross-power matrix of the recorded pressures generated by bedload which localizes the particle impacts on the plate. The results give correlation relationships between the number of signal impulses per particle mass, the amplitude, and the centroid frequency and the bedload grain size. The findings of this study contribute to the measurement of the bedload transport with the PMA system, which helps to localize the bedload impact positions and improves the predictions of particle size.