| Measurements of Lake Current by using a Radar |
| S. ENDOH, I. OKAMOTO, Y. OKUMURA, T. TAMURA, K. TAKANO, Y. HAMAI T. KODANI, Y. HAYAMI, H. ASADA, H. KAWAMURA and K. IWANE |
| Mem. Fac. Educ. Shiga Univ., Vol.37, 27-38, 1987 |
| In order to reveal the spatial distribution and time variation of water movement in Lake Biwa, a new method of drifter-tracking by using a radar has been developed. In this paper, the method and some results of recent observations are described. By using a radar which is set on the lake shore or the island, it is possible to trace many drifters simultaneously even in the night time and under the bad weather condition. The position of a drifter which is constructed by a reflector, a buoy, a rope and a window-shade drogue, is photographed at constant time intervals. The accuracy of the reading of the position of a drifter is a distance of 0.01 nautical mile and an angle of one degree. A counterclockwise gyre in the north basin of Lake Biwa has been observed for three years by a radar which was set on the top of Takeshima Island. Some drifters, especially, drifters with window-shade at 10m-depth, moved round the center of this gyre once in about two days. A clockwise gyre which exists in the southern area of a counterclockwise gyre, has also been measured in 1986, and drifters made a round once in two days. The positions of these gyre are much different from that estimated in the past. In addition, this observational method revealed the characteristics of the coastal current, inertia oscillation, internal waves, horizontal divergence and so on. The measured movement of a drifter should be made a correction of drag forces due to the wind and the vertical distribution of the lake current. |