A position dependent wave vector amplitude of vibrations on a surface of a structure is determined from acoustic measurements using a sensing device at distance from the surface. The device contains an array of microphones in a fluid medium outside the structure. Vibrations in the structure, which travel through the structure e.g. as Lamb waves. This generates sound outside the structure by leakage of sound waves from the surface of the structure. The microphones obtain measured signals from the sound. Furthermore, a measurement of such as distance is obtained that depends on the measurement position where the array of microphones is provided. The parameter is used in an inverse wave field propagation model for sound propagation in the fluid medium between the surface of the structure and the array of microphones. The inverse wave field propagation model is applied to the measured signals to obtain a position dependent estimation of the sound amplitude and/or phase at the surface. The wave vector amplitude of the vibration as a function of position on the surface is computed from the position dependent estimation.