An acoustic imaging system for the concurrent measurement of suspended sediment concentration and particle velocity

Abstract

This paper presents work on a system providing concurrent concentration and two-dimensional (2-D) particle velocity measurements on suspended sediments in water. The paper shows how one-dimensional methods for independent measurement of sediment concentration and particle velocity can be combined and extended to provide the concurrent 2-D information. An experimental system is described in which suspensions of 0.5-mm diameter sand are illuminated by acoustic burst signals of 1-MHz frequency from two transducers. The relevant theory for determining sediment concentration and particle velocity is presented. The system geometry provides for the illumination of a 5-cm3 volume at ranges of up to 1.1 m, although longer ranges are possible. Results are presented for concurrent concentration and particle velocity measurements for a falling curtain of sediment, and these are shown to be consistent with predicted values. The measurements have sufficient resolution, and can be made sufficiently rapidly, to investigate short time-scale phenomena in hydraulics, such as the effect of wave dynamics on sediment transport. The method presented could form the basis of an instrument giving sequenced acoustic images of the transport phenomena occurring within an observed volume.