Accuracy of a laser doppler velocimeter for instantaneous velocity measurements on rotating solid surfaces

This paper presents the results of an analytical and experimental investigation of the accuracy of a laser Doppler velocimeter (LDV) for solid surface velocity measurements made over very short averaging times (less than a millisecond). Fundamental limitations exist on the accuracy of such “instantaneous” measurements. For frequency domain signal processing (spectrum analysis) the accuracy is limited by finite transit time broadening and, in the case of a rotating surface, tangential velocity gradient broadening. For time domain processing (time period measurement) the accuracy is limited by stochastic phase variations in the nominally sinusoidal signal. Experiments were conducted using both signal processing techniques to determine the conditions needed to minimize the error in instantaneous measurements using the LDV. An analysis of the relative performance of a laser speckle velocimeter is also included.