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Evaluation of virtual source beam configurations for rapid tomographic reconstruction of gas and vapor concentrations in workplaces.
Park DY; Yost MG; Levine SP
J Air Waste Manage Assoc 1997 May; 47(5):582-591
An evaluation of virtual source beam configurations for rapid tomographic reconstruction of gas and vapor concentrations in workplaces by open path/Fourier Transform infrared (OP/FTIR) spectroscopy was performed. Three virtual source beam configurations generated for a single beam steerable OP/FTIR system were tested in a 24 by 21 feet (ft) chamber. The first had the spectrometer placed at the center of the chamber with 52 flat mirrors placed along the perimeter of the chamber and a retroreflector placed at each of the four corners. The second had the spectrometer placed at the center of the chamber, 52 flat mirrors placed along the perimeter of the chamber, two retroreflectors at each of the four corners, and 44 small retroreflectors placed between the flat mirrors. The third configuration had the spectrometer placed at the center of the chamber, 56 flat mirrors placed along the perimeter of the chamber, and 56 small retroreflectors placed between the mirrors. The three configurations were evaluated numerically by calculating Gaussian peak concentration profiles for an air contaminant released in the chamber which were then used to reconstruct a map of the contaminant concentrations in the chamber by computed tomography (CT). The pixel size for the calculations was set at 1.6 by 1.6ft which resulted in a 13 by 15 CT reconstruction grid. The calculated CT maps for each configuration were then compared to experimental CT maps reconstructed from data obtained when sulfur-hexafluoride was released into the chamber. Calculated CT maps generated with the third configuration, with 56 flat mirrors and 56 small retroreflectors arrayed along the perimeter of the chamber, showed the best agreement with the experimental data. Reconstructed maps for all configurations, however, showed some unrealistic artifacts such as very steep and high concentration gradients at some pixels. The authors conclude that despite the minor artifacts, the third beam configuration could be applied in many industrial situations with reasonable cost and resources.
NIOSH-Publication; NIOSH-Grant; Grants-other; Analytical-methods; Optic-system; Infrared-spectroscopy; Spectrographic-analysis; Visual-images; Computers; Industrial-hygiene; Workplace-monitoring; Mathematical-models; Laboratory-testing; Simulation-methods
Environmental & Indust Health University of Michigan 1420 Washington Heights Ann Arbor, MI 48109-2029
Issue of Publication
Other Occupational Concerns; Grants-other
Journal of the Air and Waste Management Association
University of Michigan at Ann Arbor, Ann Arbor, Michigan
Page last reviewed: October 26, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division