Mitigation of speckle noise due to laser Doppler vibrometer motion across a vibrating target.

Abstract

Laser Doppler vibrometers (LDVs) are widely used for remote vibration measurements. In many applications, such as measurements with an LDV on a moving platform or measurements with a continuously scanning beam, an LDV beam moves across a target. The motion of a laser beam across the target generates noise at the LDV output due to dynamic speckles—speckle noise. Speckle noise is caused by phase fluctuations of laser speckles and by Doppler signal dropouts and increases with the speed of the beam. It has been observed that the noise floor increase due to speckles follows a logarithmic curve as the speed increases. Of course as the speed increases, the dwell time over the target area decreases, which limits the signal of interest. This smaller sampling of the vibration signal, combined with the increase in noise due to speckles, places a severe limit on the scanning speed. A way is being investigated to take advantage of this nonlinear increase in noise with respect to speed by using time multiplexing of mul...