Uncertainty characterization of particle depth measurement using digital in-line holography and the hybrid method

Abstract

In the detection of particles using digital in-line holography, measurement accuracy is substantially influenced by the hologram processing method. In particular, a number of methods have been proposed to determine the out-of-plane particle depth (z location). However, due to the lack of consistent uncertainty characterization, it has been unclear which method is best suited to a given measurement problem. In this work, depth determination accuracies of seven particle detection methods, including a recently proposed hybrid method, are systematically investigated in terms of relative depth measurement errors and uncertainties. Both synthetic and experimental holograms of particle fields are considered at conditions relevant to particle sizing and tracking. While all methods display a range of particle conditions where they are most accurate, in general the hybrid method is shown to be the most robust with depth uncertainty less than twice the particle diameter over a wide range of particle field conditions.

Developments in digital in-line holography enable validated measurement of 3D particle field dynamics

“…Notice, this is significantly less than the estimated depth-of-focus,  ≈ 400 mm, as reported in § 1.2 for these conditions. Similar results are also reported in a few conference proceedings [6][7][8][9] as well as an in-depth article on uncertainty quantification published in Optics Express [5]. Again, readers are referred to these works for further details.…”

“…(4) and apply focus metrics to the numerically refocused images in order to extract the morphology and 3D location of in-focus particles (for examples see [4,5,15,16]). The accuracy of a given method, especially with respect to the z-position, is a strong function of the chosen focus metric and other processing details.…”

“…The method works by searching for regions in 3D space which display a minimum of intensity within the interior of the region and a maximum sharpness along outer edges of the region. This method was first proposed in a conference proceeding [6] and later published, with further details, in an Applied Optics article [4] and an Optics Express article [5]. For method specifics, readers are referred to those works.…”

“…This report summarizes developments in DIH obtained during the course of a Laboratory Directed Research and Development (LDRD) project at Sandia National Laboratories spanning the January 2011 to December 2013 timeframe. Following a brief explanation of the underlying principles and challenges, specific developments are presented with reference to a number of published works [3][4][5][6][7][8][9][10][11][12][13]. Figure 2 shows the basic experimental configuration of DIH.…”

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

“…Thus, various focus detection methods have been proposed to improve the accuracy of depth position [13,[24][25][26][27], and each claimed it can accurately locate the particles with a small error of z err , especially referring to the relative depth error z z / err . In the Gabor inline holography configuration, the depth position uncertainty z err usually equals to several times of the particle diameter and increases with the particle size, ranging from dozens of up to thousands of micrometers [12,20,21]. This uncertainty could be acceptable for 3D position determination in some applications.…”