Pd. Thorne et Pj. Hardcastle, ACOUSTIC MEASUREMENTS OF SUSPENDED SEDIMENTS IN TURBULENT CURRENTS AND COMPARISON WITH IN-SITU SAMPLES, The Journal of the Acoustical Society of America, 101(5), 1997, pp. 2603-2614
Increasingly in recent years the application of acoustic backscatterin
g to the quantitative measurement of suspended sediment particle size
and concentration at sea has gained acceptance. A number of works desc
ribing the interaction of sound with suspensions have been published,
and the scattering properties of suspended sediments formulated. Howev
er, there have been relatively few experiments conducted in the marine
environment, which have attempted to assess the accuracy of the acous
tic measurements by direct comparison with in-situ samples, taken simu
ltaneously with the acoustic observations. The purpose of the present
work is to report on such an experiment, and to evaluate the accuracy
of the acoustic technique. To this end multifrequency acoustic measure
ments of suspended sediment profiles were collected in an estuarine en
vironment, subject to strong turbulent tidal currents, which generated
high concentrations of suspended sediments. To obtain the sediment pa
rameters from the acoustic data an inversion needs to be applied, and
this inversion is examined here in some detail, particularly for the c
ase when sediment attenuation is substantial. To assess the sediment p
arameters derived from the acoustic inversion, mean acoustic estimates
of particle radius and concentration are compared with the benchmark
of in-situ pumped sampling. In addition to the analysis of the mean da
ta, high-resolution images of the suspension dynamics have been genera
ted, and the validity of these observations appraised by evaluating th
e internal consistency of the multifrequency results. (C) 1997 Acousti
cal Society of America.