Lidar frequency modulation vibrometry in the presence of speckle

Abstract

We report laboratory target vibration measurements that use an easily aligned and adjusted fiber-based 1.5-microm heterodyne lidar. The targets are simple spherically curved retroreflectors with well-controlled vibration frequencies and amplitudes. A rotating ground-glass screen creates Gaussian speckle. We wish to understand the modulated and fast-fading lidar returns seen from real target. We frequency demodulated the recorded laboratory data by phase differencing to provide estimates of dphi/dt, where phi is the phase of the received carrier-plus-noise phasor. Experimental results for signal strength and signal-to-noise ratio, for specific target modulation parameters, agree well with our recently developed dphi/dt correlation-function theory.

Advanced signal processing methods for pulsed laser vibrometry

“…The vibration amplitude is chosen so that the modulation bandwidth is of the same order. Such values are consistent with the actual parameters expected for long range moving vehicle identification (previous studies [6,8] considered speckle noise with lower bandwidth, few hundred Hertz). The CNR, averaged in time, is a common parameter for all operating modes, given the hypothesis of equal mean laser power in every case.…”

“…The random speckle pattern backscattered by the target is not static if the illuminated surface is moving, and as a consequence the amplitude and phase of the received wave will vary, a phenomenon either called "speckle noise" or "target decorrelation noise" in literature [8]. The resulting multiplier has a complex normal distribution and autocorrelation function Γ(τ) = exp(-…”

Lidar for Turbine Control: March 1, 2005 - November 30, 2005

“…Bistatic CW lidar systems (with separate transmit and receive optics) are commonly used for hard-target applications such as vibrometry [25]. Bistatic CW wind lidars have also been successfully demonstrated [16] (Figure 7) and have the advantage of improved probe volume definition.…”

Adjustment of Measurements with Multiplicative Errors: Error Analysis, Estimates of the Variance of Unit Weight, and Effect on Volume Estimation from LiDAR-Type Digital Elevation Models

“…LiDAR has been widely used to construct DEM (see e.g., [37,39,40,43–45]). Although LiDAR measurements have been proved, both theoretically and experimentally, to be of multiplicative random errors (see e.g., [49–51]), they have been treated as if they were of additive error nature in DEM construction. Thus, this section is to serve two major purposes through numerical simulations: (i) to investigate the effect of LiDAR-type measurements on DEM construction; and (ii) to collectively use the error analysis and the estimates of the variance of unit weight given in the previous two sections to estimate the errors of the volume of landslide mass, since a precise estimate of the volume of a landslide from the constructed DEM can be important in practical hazard evaluation.…”