Three-Dimensional Flow Measurement by Digital Holographic Particle Image Velocimetry with Spatio-Temporal Derivative Method (Evaluation of the Measurement Accuracy by Numerical Simulation)

Abstract

In this paper, we present a digital holographic particle image velocimetry (DHPIV) technique with a spatio-temporal derivative method for velocity measurement in 3D space and the results of evaluating on its measurement accuracy. In this technique, hologram patterns are observed as digital images using an electronic camera, such as CCD or CMOS, and image reconstruction is carried out on a personal computer. Since an in-line observation system is utilized in conventional digital holography, a numerically reconstructed image is considerably enlarged in the depth direction and its depth resolution is extremely low; hence, the measurement accuracy in the depth direction is inaccurate in a digital holographic measurement. To overcome this difficulty, we apply a spatio-temporal derivative method to this technique for the detection of particle displacement along the z-axis. In a numerical simulation, measurement accuracy is evaluated for a multi particle model and a cubic cavity flow model. Furthermore, we examine the effect of noise on displacement measurement accuracy for numerically constructed noisy hologram patterns.

Measurements of pollen grain dispersal in still air and stationary, near homogeneous, isotropic turbulence

“…Lu et al, 2008), various criteria have been proposed for detecting the best in-focus plane of a particle (e.g. Yamaguchi et al, 2006). Here, we defined the in-focus particle depth position as the location where the reconstructed light intensity averaged over the reconstructed particle image, was locally minimal.…”

Characterization of particles suspended in a volume of optical medium at high concentrations by coherent image processing

“…Most current digital PIV and LSV imply the use of cross-correlation analysis in order to obtain information about velocities. 31 that the inline holography method cannot reliably determine the particle. In this case, the image correlation algorithm gives the mean displacement of this mixed structure, which leads to noise and poor accuracy.…”

Measurement of pollen clump release and breakup in the vicinity of ragweed (A. confertiflora) staminate flowers

“…The particle's depth position (x 2 ) was determined by the location where the reconstructed light intensity averaged over the reconstructed particle image, was locally minimal (see Sabban and van Hout 2011). Because of in-depth position inaccuracy inherent to single view holography technique (e.g., Yamaguchi et al 2006, Lu et al 2008, we fitted the determined x 2 in-focus positions that suffered from high noise levels, by a second order polynomial, assigning increased weight to the start and end positions that were carefully manually checked.…”