Abstract: Analytical expressions for the crosscovariance(time-of-flight velocimeter, LTV) and for the powerspectrum (laser Doppler velocimeter, LDV) are presentedbased on the assumption of all apertures having aGaussian transmission function. The objects aresimulated at solid targets having lateral spatialcorrelation, i.e. giving rise to partially developedspeckle. The case of fully developed speckle can thusbe simulated by having zero correlation length. Forboth systems and either target the relative width ofthe crosscovariance (LTV) and power spectrum (LDV) iscalculated analytically based on the entire opticalsystem and expressed as a function of the number ofmodes in the detection system. It is shown that the LTVwill give in general a lower variance for the velocityestimate but that spatial correlations of the targetare most detrimental to the LTV system. Besides, thedecorrelation effects for measurement on curvedsurfaces are considered and it is shown that bothsystems will suffer equally in the case of a multimodesystem but the LTV system will be superior to an LDVsystem in case of a single mode system. The basicdifference between the performance of the two systemsstems from the inherent difference in bandwidth. !9
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