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

鼠河附近的封闭微咸水有分层的淡水和咸水，由于受大气和天文现象的影响，流场复杂，水质存在低氧、咸水等各种问题；风的压力，大气压力的变化，潮汐流动。近年来，流量的野外测量主要采用ADCP、DGPS等测量设备。然而，由于湖泊面积大，流场测量困难，本研究开发了一种用于测量分层封闭微咸水中水流的跟踪点系统。它是一种手持式测量系统，它跟随着漂浮应答器随分层水面移动的三维坐标点。该系统利用坐标时间点的移动平均值，与DGPS相比具有足够的精度，测量范围约为1公里。我们应用该系统对岛根县中尾湖的Yonago Bay的流量进行了测量。结果表明，分层水中的漂浮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一致。进一步研究表明，潮流作用下的分层水运动范围约为几公里，纳考米湖的流场受风、气压、几何等因素的影响较大。

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.