Acoustic backscatter and attenuation due to river fine sediments:
experimental evaluation of models and inversion methods
Abstract
The hydroacoustic monitoring of suspended sediment concentration (SSC)
in rivers is based on the inversion of backscatter and attenuation
models. To evaluate such models, acoustic backscatter and attenuation
were measured from a homogeneous suspension of fine river sediments
(clay) in a laboratory tank at various concentrations in the range 1-18
g/l. Agreement between the modelled and measured acoustic backscatter
and attenuation values was found to be relatively poor. The results are
highly sensitive to particle size and shape which come with large
measurement uncertainties and can be significantly improved by adjusting
plausible particle parameters. Various inversion methods combining
single or multiple frequencies, analysis of backscatter and/or
attenuation, spherical or oblate shape hypothesis for particles and
fixed or estimated lognormal grain size distribution are tested. The
most promising inversion methods using both backscatter and attenuation
information led to accurate SSC estimates.