Calibration and sediment load algorithms for an acoustic sediment flux probe

Abstract

A method to infer sediment concentrations from acoustic backscatter levels has been implemented for a prototype acoustic sediment flux probe. This required calibrations of the acoustic transceiver systems and direct measurements of the system response to typical sediment size distributions over a wide range of concentrations. The sensitivities of the 1.3 MHz and 5.2 MHz transducers of an acoustic sediment probe were measured using the backscatter amplitudes from stainless steel wires of four different radii. A two-frequency inversion algorithm estimating the geometric mean radius and variance about the mean of suspended sediment with an assumed lognormal size distribution and the sediment mass concentration was developed and tested in a laboratory setting. The sensitivity of the 5.2 MHz transducer for each wire was consistent within 10%. The sensitivity of the 1.3 MHz transducer calculated for each wire was not consistent and is believed to be due to a strong angular dependence between the wire orientation and the 1.3 MHz transducer face. The sensitivities of each of the four transducers were, however, inferred from the system's response to the controlled sediment backscatter measurements.