ABSTRACT
U Ultrasonic method A method of open-channel discharge measurement using the
velocity of ultrasound (a sound with a frequency greater than 20,000 Hz) in water. It consists of two transducers M and N, installed obliquely on opposite banks of the channel, and of the apparatus to measure the ultrasound velocity. See also acoustic method; Doppler current meter; Figure U-1. The discharge Q is:
Q = ΔyL2(tan θ)/2P (U-1)
where Δ = difference between the travel times from M to N and from N back to M, P = product of these two travel times, L = distance from M to N, y = average depth of flow along the path MN, and θ = angle between MN and the direction of flow.
