DIRECT INVERSION METHOD TO MEASURE THE CONCENTRATION PROFILE OF SUSPENDED PARTICLES USING BACKSCATTERED SOUND

Acoustic backscatter using a single-frequency transducer can be used f or field measurement of irregularly shaped, suspended sediment with a given size distribution. It is assumed that the size distribution of t he suspended sediment does not change significantly along the sound pa th. A newly found explicit solution to acoustic backscatter equation i s derived. This explicit solution reduces the computation time signifi cantly during the inversion process. The near-field effect can be incl uded in the inverted quantities by calculating the initial condition w ith the far-field acoustic backscatter equation and under the assumpti on of uniform near-field concentration. This method proved successful in the laboratory with initial concentrations of sand up to 3.5 g/L. T he errors in estimation of concentration that result from errors in th e attenuation coefficients or near-field concentration are significant ly amplified with range in a uniform concentration field. However, wit h an exponential concentration profile, which is commonly found in sed iment suspension phenomena, the inversion is only weakly sensitive to attenuation coefficients associated with sound absorption by water and sound scattering by suspended particles. Near-field concentration err ors result in commensurate errors throughout the range in the exponent ial profile.