Acoustic inversions for measuring boundary layer suspended sediment processes

Abstract

Although sound has been applied to the study of sediment transport processes for a number of years, it is acknowledged that there are still problems in using the backscattered signal to measure suspended sediment parameters. In particular, when the attenuation due to the suspension becomes significant, the uncertainty associated with the variability in the scattering characteristics of the sediments in suspension can lead to inversion errors which accumulate as the sound propagates through the suspension. To study this attenuation propagation problem, numerical simulations and laboratory experiments have been used to assess the impact unpredictability in the scattering properties of the suspension has on the acoustically derived suspended sediments parameters. The results clearly show the commonly applied iterative implicit inversion can lead to calculated sediment parameters, which become increasingly erroneous with range, as the sound propagates through the suspension. To address this problem an alternative approach to the iterative implicit formulation is investigated using a recently described dual frequency inversion. This approach is not subject to the accumulation of errors and has an explicit solution. Here the dual frequency inversion is assessed and calculated suspended sediment parameters are compared with those obtained from the iterative implicit inversion.

Measuring particle concentration in multiphase pipe flow using acoustic backscatter: Generalization of the dual-frequency inversion method

“…A model, described by Thorne and Hanes (2002) and Thorne et al (2011), for which the acoustic properties of suspended particles have only been published for quartz-type sand, was adapted such that the attenuation and backscatter coefficients, n h and K h , for particles of arbitrary physical properties can be measured experimentally and used in a dualfrequency concentration inversion method . Coefficients for four particle species (two types of glass sphere with median diameters of d 50 ¼ 44 and 71 lm, and two types of jagged plastic bead, d 50 ¼ 468 and 691 lm) were measured.…”

“…The model described by Thorne and Hanes (2002) and Thorne et al (2011) for marine sediment was chosen for use in this study because it is simpler to implement than some other, similar formulations (Carlson, 2002;Furlan et al, 2012;Ha et al, 2011) and has a firm theoretical basis (Hay, 1991;Kyt€ omaa, 1995;Richards et al, 1996). As a result, it has previously been employed by a number of groups (Admiraal and Garc ıa, 2000;Hunter et al, 2012a;Hurther et al, 2011).…”

“…Indeed, Challis et al (2005) are particularly keen to emphasize the benefits of ultrasonic methods, since one particularly useful capability of such methods is to interrogate suspensions of much higher concentrations than is possible with optical methods. In this study, an acoustic model developed and used extensively by marine scientists (Thorne and Hanes, 2002;Thorne et al, 2011) has been adapted in a novel way. The model relates the backscattered acoustic signal received by an active piezoelectric transducer to the properties of the particles in a suspension, and has been employed by a number of groups (Admiraal and Garc ıa, 2000;Hunter et al, 2012a).…”

Measurement of particle concentration in horizontal, multiphase pipe flow using acoustic methods: Limiting concentration and the effect of attenuation

“…and [7] that such inversions are difficult because M appears more than once, and many such implicit and explicit inversion methods suffer from numerical instability in the far field (Thorne and Hanes, 2002), as described in the preceding section. However, one explicit dual-frequency inversion method Thorne et al, 2011) avoids such instabilities and the particle concentration can be calculated at any position from the transducer independently. According to this method, the particle mass concentration is obtained by algebraic manipulation of Equation [2] as follows:…”

“…A number of concentration inversion methods exist (Hanes, 2012;Hanes et al, 1988;Lee and Hanes, 1995;Thorne and Hardcastle, 1997;Thosteson and Hanes, 1998) many of which were reviewed in detail by Thorne and Hanes (2002) and Thorne et al (2011). The issue of numerical instability is an important and well known one in both implicit and explicit inversion methods, as it can cause computed particle concentrations to deviate very significantly from the true values to an extent that increases with distance from the transducer(s).…”