Improvements in acoustic sediment concentration profiling using an LMS compensation algorithm

In sediment concentration profiling, sound attenuation becomes important for high-frequency acoustic backscattering systems (ABSS) when sediment concentration is high and/or the range of remote sensing is long. In the present study, a test of a least mean square (LMS) compensation algorithm was performed in order to determine the advantages over the more frequently used iteration algorithm. Numerical simulation and laboratory experiments in a mixing tank as well as an open channel suggest that the new algorithm is much more robust to white Gaussian noise and fixed-echo noise, and errors do not accumulate along the profiling path. Good linearity of this instrument in concentrations up to 20 kg/m^-3 is found by comparison with a suction-sampler. In the mixing tank, backscattering intensity profiles in concentrations up to 120 kg/m^-3 vary little along a propagation path of 40 cm and fit well to the expected homogeneous concentration. Furthermore, by using the oscillation errors in the LMS solution, a procedure has been developed to compensate for the errors in the instrument constants evaluated from the attenuation between the transducer and the first measuring volume. The feasibility of the proposed instrument-constant compensation is verified by experiments. This allows instantaneous correction of the influence of sediment deposition on the transducer surface which is important when the system is applied to coastal investigation