A method for measuring surface displacements is described. The principle is based on the detection of the phase shift of a high frequency continuous ultrasonic wave reflected from the moving surface. The analysis shows that the long time delay undergone by the ultrasonic wave produces a significant enhancement of the Doppler phase shift signal. Experiments were carried out in water with a 30‐MHz focused transducer probe and transient mechanical displacements smaller than 1 A˚ (surface velocities smaller than 1 mm/s) were detected in a 10 MHz bandwidth. ©1995 American Institute of Physics.