The interpretation and evaluation of a 3-MHz acoustic backscatter device for measuring benthic boundary layer sediment dynamics

Abstract

For ultrasonic backscatter devices to be of aid in studies of turbulent sediment transport dynamics, the procedures for converting signal to concentration estimates should be as accurate as possible, and the space and time resolution should be as high as possible. Signal conversion for the 3-MHz system considered here takes into account nearfield beam pattern effects on propagation and attenuation. Enhancing resolution involves explicit consideration of various sources of noise and interference. The results of field deployments demonstrate that, with signal conditioning and ensemble averaging, signal-to-noise ratios can be achieved that allow turbulent variation in concentration to be measured. Two possible sources of error in the conversion procedure are: (1) attenuation due to scatters is not measured in situ, but must be estimated from the data, and (2) with a single-frequency beam, the effects on scattering response of concentration variation and particle-size variation cannot be uncoupled.