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

鼠河附近封闭的微咸水域，由于受大气和天文现象影响的复杂流场，存在着淡水层和咸水层的分层，存在着低氧、含盐量高等水质问题；例：风的压力，大气压力的变化，潮汐。近年来，ADCP、DGPS等测量设备被广泛应用于水流的野外测量。但由于湖泊面积大，流场的测量难度较大。在本研究中，开发了用于测量分层封闭咸淡水水流的跟踪点系统。它是一种跟踪随分层水体移动的浮动应答器三维坐标点的精确测量系统。该系统利用坐标点在时间上的移动平均值，与DGPS相比具有足够的精度，测量范围约为1 km。我们将该系统应用于岛根县中海湖与古湾的流量调查。结果表明，分层水中的浮动应答器可以跟随周围的移动水，其移动速度与ADCP测量的相同。结果表明，潮汐作用下分层水的移动范围约为几公里，中见湖的流场受风、气压、几何形状等因素的影响较大。

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.