Statistical behaviour of laser Doppler vibrometer detector signals and application of statistics for signal diversity

Abstract

The problem of speckle noise and the so-called signal dropouts is well-known by many LDV sensors. Signal power is reduced when less light power is scattered into the detection aperture due to laser speckle. Signal dropouts occur when the carrier-to-noise ratio (C/N) of the photodetector signal falls below the frequency modulation (FM) threshold. This problem can be resolved with signal diversity. However, the influence of the speckle noise and signal dropouts has not been quantitatively analysed the state of the art. We introduce in this paper a new mathematical model of the statistical behaviour of detector signals of LDV sensors. This allows us to calculate the influence of speckle noise and signal dropouts on the detector signals of LDV sensors. Furthermore, we optimize the signal combination method of signal diversity according to the state of the art. Finally, we present some experimental results to prove our mathematical model and signal diversity for reducing speckle noise and signal dropouts.