IMPROVEMENTS IN ACOUSTIC SEDIMENT CONCENTRATION PROFILING USING AN LMS COMPENSATION ALGORITHM

In sediment concentration profiling, sound attenuation becomes importa nt for high-frequency acoustic backscattering systems (ABSS) when sedi ment concentration is high and/or the range of remote sensing is long, In the present study, a test of a least mean square (LMS) compensatio n algorithm was performed in order to determine the advantages over th e more frequently used iteration algorithm. Numerical simulation and l aboratory experiments in a mixing tank as well as an open channel sugg est that the new algorithm is much more robust to white Gaussian noise and fixed-echo noise, and errors do not accumulate along the profilin g path. Good linearity of this instrument in concentrations up to 20 k g/m(-3) is found by comparison with a suction-sampler. In the mixing t ank, backscattering intensity profiles in concentrations up to 120 kg/ m(-3) vary little along a propagation path of 40 cm and fit well to th e expected homogeneous concentration. Furthermore, by using the oscill ation errors in the LMS solution, a procedure has been developed to co mpensate for the errors in the instrument constants evaluated from the attenuation between the transducer and the first measuring volume. Th e feasibility of the proposed instrument-constant compensation is veri fied by experiments. This allows instantaneous correction of the influ ence of sediment deposition on the transducer surface which is importa nt when the system is applied to coastal investigation.