DETERMINING SUSPENDED SAND SIZE AND CONCENTRATION FROM MULTIFREQUENCYACOUSTIC BACKSCATTER

An inversion algorithm for extracting suspended sand size and concentr ation from simultaneous backscattered acoustic pressure amplitude at t hree operating frequencies is presented. The algorithm is based on the differences in signal amplitude between different frequency pairs, an d is tested using laboratory measurements of multifrequency backscatte r from a turbulent sediment-carrying jet. Concentration and size profi les inverted from field and laboratory data are compared with results from a previously developed algorithm based on signal ratios. The diff erence inversion scheme is less sensitive to errors arising from low s ignal levels, allowing the size/concentration measurement range to be extended to regions of lower concentration. The concentrations from th e field data agree well with independent optically determined estimate s. The results demonstrate sensitivity to the backscatter form factor.