A simplified method for determining sediment size and concentration from multiple frequency acoustic backscatter measurements

Abstract

Until recently the determination of concentration from acoustic backscatter intensity measurements required an iterative technique due to the implicit form of the acoustic backscatter equation. In this paper, an explicit form of this equation is examined in an effort to simplify the technique of determining size from multifrequency acoustic backscatter data. By retaining the size dependence throughout the derivation for an explicit solution for concentration, a new explicit form results. This new explicit concentration solution improves the technique for determining median sediment size by incorporating sediment attenuation in the calculation. Because this new technique relies on the minimization of the variance in concentration as determined by different frequency transducers, the previous technique of pairing transducers of different frequencies is replaced by a technique making use of any number of different frequency transducers. The new size/concentration inversion technique is tested using both simulated and laboratory data. Numerical precision is shown to be the only source of error with the use of simulated data. Laboratory tests result in less than 20% error in the determination of both concentration and size over a range of nearly one meter.

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