A SIMPLIFIED METHOD FOR DETERMINING SEDIMENT SIZE AND CONCENTRATION FROM MULTIPLE FREQUENCY ACOUSTIC BACKSCATTER MEASUREMENTS

Until recently the determination of concentration from acoustic backsc atter intensity measurements required an iterative technique due to th e implicit form of the acoustic backscatter equation. In this paper, a n explicit form of this equation is examined in an effort to simplify the technique of determining size from multifrequency acoustic backsca tter data. By retaining the size dependence throughout the derivation for an explicit solution for concentration, a new explicit form result s. This new explicit concentration solution improves the technique for determining median sediment size by incorporating sediment attenuatio n in the calculation. Because this new technique relies on the minimiz ation of the variance in concentration as determined by different freq uency transducers, the previous technique of pairing transducers of di fferent frequencies is replaced by a technique making use of any numbe r of different frequency transducers. The new size/concentration inver sion technique is tested using both simulated and laboratory data. Num erical 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 t he determination of both concentration and size over a range of nearly one meter. (C) 1998 Acoustical Society of America. [S0001-4966(98)061 08-6]