Field survey on the flow field in a enclosed brackish lake by using the Track point system

河鼠附近封闭的半咸水沃茨，由于受大气和天文现象的影响，流场复杂，存在着淡水和咸水分层，从而出现了低氧、咸水等各种水质问题。风的应力，大气压力的变化，潮汐流。近年来，ADCP、DGPS等测量设备被用于水流的现场测量。本研究利用追踪点系统，对分层封闭的半咸水沃茨进行流场量测。它是一种跟随随分层水体运动的浮动应答器的三维坐标点的一致性测量系统。该系统采用时间坐标点的滑动平均值，与DGPS相比具有足够的精度，测量范围约为1km。我们应用该系统调查岛根县中海湖的约纳戈湾的水流。结果表明，在分层水体中，应答器能够跟随周围的运动水体运动，其运动速度与ADCP同时测量的运动速度相同。进一步研究表明，潮流引起的分层水移动范围约为几公里，中海湖的流场受风、气压、几何形状等因素的影响很大。

Enclosed brackish waters near the river mouse has stratified layers of freash and salty water, so that there are the various problems on the water quality such as low oxygen, salinity water and so on because of complex flow field affected by atmospheric and astronomical phenomena; ex. Stress of wind, change in atmospheric pressure, tidal flows. Recently, measurement devices such as ADCP, DGPS and so on are used for the field survey on flows. However, the measuring of flow fields is difficult because of the large area of lake.In this research, Track point system is developed for surveying the flows in a stratified and enclosed brackish waters. It is one accorstic survey system which follow the 3D coordiate-point of the floating transponder which move with the stratified water. This system has the sufficient accuracy compared with DGPS by using the moving average value of the coordinate-point in time and has the measuring range about 1 km. We apply the this system to survey the flows at Yonago Bay of Nakaumi Lake in Shimane Prefecture. As results, it was revealed that the floating transponder in the stratified water can follow the moving water surround it and its moving speed is same with one measured by ADCP at the same time. Further, it was shown that the moving range of stratified water due to the tidal flows is about a few km and the flow fields in Nakaumi Lake is greatly affected by wind, atmospheric pressure, geometry and so on.