Direct particle depth displacement measurement in DHPTV using spatial correlation of focus metric curves

In-Situ Characterization of Coal Particle Combustion via Long Working Distance Digital In-Line Holography

“…Particles in the hologram pair are first identified and then matched in a 2D way by using the Hungarian algorithm, which minimizes the total distance to yield the globally most possible pairing of particles in sequential frames. The x – y displacement is calculated by a simple subtraction, while the z displacement was calculated directly with a focus correlation method because of the lower z location accuracy . The particle velocity is then derived from the displacement and the time interval ( v x = δx / δt , v y = δy / δt , v z = δz / δt ).…”

“…The x − y displacement is calculated by a simple subtraction, while the z displacement was calculated directly with a focus correlation method because of the lower z location accuracy. 57 The particle velocity is then derived from the displacement and the time interval (v x = δx/δt, v y = δy/δt, v z = δz/δt). Figure 8 demonstrates the 2D and 3D velocity field from a pair of hologram recorded at the outlet of the burner.…”

Simultaneous measurement of 3D velocity and 2D rotation of irregular particle with digital holographic particle tracking velocimetry

“…Previous investigations [35] revealed that focus metric curves Fc 1 and Fc 2 present essential spatial correlation in the depth direction: Fc 1 (z + Δz)~Fc 2 (z), and that the depth displacement Δz gives rise to the local shift between the two curves. Thus, the depth displacement Δz can be directly and accurately measured from the global space shift between the two curves, and the cross correlation of Fc 1 (z) and Fc 2 (z) is employed to evaluate the spatial shift of the focus metrics:…”

“…This algorithm is more accurate and robust. What's more, it avoids the uncertainty inherited from the error of depth position determination [35]. Fig.…”

“…Due to the attractive advantages, digital holography has shown great potential in the 3D diagnostics of particle field [27]. Digital holography not only is capable of measuring the particle's shape, size and 3D position at the reconstructed in-focus image [28][29][30], but also can be extended to measure the 3D velocity in a manner of particle tracking/image velocimetry (PTV/PIV) [9,[31][32][33][34][35], called digital holographic particle tracking/image velocimetry (DHPTV/DHPIV). The 3D reconstruction, particle detection, 3D locating and 3D velocity evaluation have been comprehensively investigated, and successful applications of DHPTV/PIV to measure various particle fields, including irregular solid particles, droplets, microorganisms or cells and tracers in turbulence, have been demonstrated.…”