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

为了了解河流输沙和河床形态变化的机理，对二维或三维含沙量分布的瞬时测量有很高的需求。然而，目前，沉积物浓度检测的唯一手段是光电电池装置。我们打算通过应用CT（计算机断层扫描）技术开发一种用于瞬时测量二维或三维沉积物浓度的仪器。特别针对以下项目：(1)仪器不得分配流场。(2)测量是瞬间完成的。(3)仪器应小巧便携，既可用于实验室，也可用于野外。(4)仪器的价格尽可能低，供普通研究人员使用。一排激光发射器被放置在与平均流平行的一条线上。激光强度的扩展率由放置在相反位置的射线接收器测量和记录。浓度场可以用双Fouries级数（复变量）或虚拟板和载荷法（该方法由首席研究员hino先生于1975年提出）来表示。这个问题可以归结为一种求解线性联立方程组的计算机断层扫描。该仪器由扫描多点激光透射单元、光探测阵列和数据处理单元组成，其软件采用逆估计原理。一些实验室对实际浓度场的测试证明了该仪器的实用性。结果表明，虚载荷法优于双傅立叶级数展开法。前者可以用较少的膨胀系数来表示较复杂的浓度场，可以很容易地消除测量激光强度的误差。

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.