Abstract: In the embodiments described in the specification, an acoustic transducer unit emits acoustic signals into a moving liquid and receives reflected signals to produce Doppler frequency signals and a depth detector simultaneously detects the depth of the liquid. The Doppler frequency signals are processed in a Fast Fourier Transform unit to determine the average velocity of the liquid and a historical velocity versus depth table is prepared. Thereafter, each new velocity value is compared with an expected velocity value for the corresponding depth based on the historical table. The new velocity value is rejected if the variation from the expected value exceeds a selected variation. If accepted, the new velocity value and the expected velocity value from the table are weighted and combined to provide a new value for the table and also for a velocity versus depth profile unit. The velocity versus depth profile is adjusted based on the new velocity value using a least squares fit.