Abstract: A continuous wave ultrasonic wave transmitter transmits modulated waves in two opposite directions being intercepted by a forward receiver and an aft receiver. The received signals are demodulated and the relative phase is used to obtain a speed reading. The wave length of the modulator signal must be larger than the two, preferably equal transmitter-to-receiver spacings. A similar but orthogonally arranged receiver system permits acquisition of a speed vector. Different modulation frequencies are to be used for different speed ranges; all these frequencies are transmitted simultaneously and selection of the desired one is made in the processing circuit only.