超音波を用いた繰返し形伝搬時間逆数差法による微弱な底層流の測定

抄録

Velocity of water flow can be measured in a short time by “Repetitive Inverse Transit Time Difference Method(RITTD)” with ultrasonic pulses previously proposed.
This method was applied for 3-dimensional current meter with three pairs of sensor placed at 120° space and with the elevation angle 45° in order to measure extremely slow current in deeper layer of lake. In this instrument, it is easy to check irregular data from the sum of velocity in the three axes. Furthermore, it is possible to measure, at least, horizontal current even if missing of measurement in one axis occurs. Accuracies of 6° in direction and 5mm/s in velocity were obtained.
The practical measurement was carried out in Shiozu Bay of Lake Biwa from Oct. 12 to 17, 1990. The fluctuation velocity of tens mm/s with maximum velocity of 160mm/s were determined. They have good agreements with previous data obtained by Okamoto.
This instrument can be used for field applications.