Development of the instantaneous measurement system of 3-dimensional sediment concentration distribution by LASER sheet emission

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Need for the instantaneous measurement of 2-or3-dimensional sediment concentration distribution are high in order to understand the mechanism of sediment transportation and bed configuration changes in rivers. However, at present time, the only means of sediment concentration detection is a device applying photo-electronic cell.We intended to develop an instrument for instantaneous measurement of 2-or 3-D sediment concentration by applyng the CT (computer tomography) technique. Especially, the following items are aimed at ;(1) The instrument must not distrib flow fields.(2) The measurement is made instantaneously.(3) The instrument should be compact and portable for use in laboratories as well as fields.(4) The price of the instrument is as low as possible for use by common researchers.A row of laser emitters is placed on a line parallel to the mean flow. Extenciton rate of laser intensity is measured and recorded by ray receivers positioned on an opposite site. The concentration field is expressed either by the double Fouries series (complex variable) or by the virtual plate and load method (which has been proposed by the head investigator, M.Hino, in 1975). The problem reduces to a kind of computer tomography of solving a system of linear simulaneous equations.This instrument was constituted of a scanning multipoint laser light transmitting unit, a photo detection array and a data processing unit whose software is operated based on the principle of the inverse estimation. Some laboratory test for a real concentration field proved the usefulness of the instrument. The method of virtual load proved to be superior to the double Fourier series expansion. By the former method, a more complicated concentration field can be expressed by a lesser number of expansion coefficients, the errors included in measured LASER intensity are easily cancelled.