Noise Analysis for Laser Doppler Velocimeter Systems

Laser Doppler velocimeters provide a noncontact method for the measurement of velocities. These measurements are, in general, corrupted by noise arising in the transmission and reception of the optical carrier. An analysis is presented for the effect of noise on the output of the velocimeter system under conditions of high scattering center concentrations and Steady flows. Principally, the so-called Gaussian beam optical setup is considered where the intensity distribution of the intersecting laser beams at the observation volume (fringe pattern) is Gaussian. Output noise spectral densities, noise power, and signal-signal-to-noise ratios are derived in terms of the input signal (Doppler carrier)-tonoise ratios and bandwidths of the processing systems. Also, threshold levels for input signal-to-noise ratios are determined and the photodetector performance analyzed. Finally, analogies are drawn where the current analysis is applicable to other areas of communication.