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Summary: Experimental Investigation of the Effect of Speckle Noise on Continuous
Scan Laser Doppler Vibrometer Measurements
Michael W. Sracic
&
Matthew S. Allen
University of Wisconsin-Madison
535 Engineering Research Building
1500 Engineering Drive
Madison, WI 53706
Abstract
Continuous Scan Laser Doppler Vibrometry (CSLDV) sweeps a laser spot continuously over a structure to
measure its mode shapes at hundreds of points simultaneously. It can be used to measure accurate, detailed
mode shapes using a hand-held impact hammer, while conventional point-by-point LDV can be impractical and
inaccurate in that application because of strike-to-strike variation in the impact location and orientation. Recently
presented techniques can be used to transform the CSLDV measurements into a set of responses that can be
processed using standard system identification techniques to extract the modes. The resampling method works
best when the scan frequency is high relative to the highest natural frequency of interest, and state of the art
scanning vibrometers are capable of relatively high scan frequencies, but there is a tradeoff between
measurement quality and scan frequency due to laser-speckle noise. This work explores the effect of LDV
measurement noise, both the periodic and non-periodic components, on CSLDV measurements. Of particular
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