Development and uncertainty characterization of 3D particle location from refocused and perspective shifted plenoptic images

Abstract

In recent years, the development of non-invasive 3D diagnostics has become a significant area of research due to the wide variety of available techniques and the multitude of engineering problems that benefit from these measurements. This dissertation is motivated by the need to measure explosively generated fragment fields in 3D and utilizes a plenoptic camera to measure fragment or particle characteristics. Plenoptic imaging is an implementation of light field imaging in which a camera is modified by the insertion of a microlens array between the main lens and the image sensor which allows instantaneous collection of 3D data from a single snapshot by extracting the volumetric information in post-processing. This work details the development of algorithms to determine 3D position and in-plane size and shape of particles by exploiting the refocusing and perspective shift capabilities of a plenoptic camera. These algorithms are validated using a large experimental data set in which a static particle field is translated to provide known depth displacements at varied magnification and object distances. Examination of these results to determine quantitative measures of uncertainty indicates improved accuracy and precision is achieved through the use of perspective shifting as compared to the refocusing based method at significantly reduced computational costs. The perspective shift method is further applied to fragment localization and sizing in a lab scale fragmenting explosive and measurement of the secondary droplet field created by the impact of a drop of water on a thin film of water. In tandem with the development of these particle location algorithms a method of volumetric calibration of a plenoptic camera is implemented and tested.