Author(s): C. P. Lenn; K. J. Enever
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Keywords: No Keywords
Abstract: In order to measure sand transport in estuaries an instrument has been developed, and tested in the laboratory to give in situ simultaneous measurement of size and concentrat ion. The theory of ultrasonic scattering is presented and shows that an appropriate choice of frequency and scattering geometry will give greatly reduced sensitivity to silt sized particles (< 60 um diameter) whilst yielding the required information. L aboratory exper iments were conducted using a vertical sedimentation test facility and single angle scattering and showed that the behaviour of ultrasound scattered from narrow size distributions of glass ballotini and sand is adequately modelled by the theory. A laboratory model of a field instrument, employing analogue and digital signal processing, was then con- structed and tests were performed on sediments of wider size distribution. The ratio of ultrasound scattered through 100 and 170° was found to be concentrat ion independent, being a function of size only. The backscattered signal, suitably processed, was a measure of concentration and was linear, temperature independent, and relatively insensitive to the presence of silt.
Year: 1985