Experimental evaluation of an environmental CAT scanning system for mapping chemicals in air in real-time

An innovative method is being developed which creates real-time, two-dimensional maps of chemical concentrations in air for environmental and occupational applications. This method, we call environmental CAT scanning, combines the real-time measuring technique of open-path Fourier transform infrared spectroscopy with the mapping capabilities of computed tomography to produce accurate spatial and temporal information about contaminant concentrations and dispersion patterns. With this system, a network of open-path measurements is obtained over an area; measurements are then processed using a tomographic algorithm to reconstruct the concentrations. This article describes a thorough experimental evaluation of an environmental CAT scanning system using a field-ready prototype system deployed in a room-size exposure chamber; point sample measurements were taken simultaneously in the chamber along with the CAT measurements. Twenty-eight experiments were performed using single or multiple plumes of a tracer gas in the chamber. Tomographic maps were compared with the point sample reference maps to evaluate the CAT scanning system for accuracy of concentration measurement and plume location. Quantitative agreement was very good; concentrations reconstructed with the tomographic maps agreed to within 17 percent of the point sample maps, and plume locations were reconstructed to within six inches of the plumes in the point sample maps. This technique shows real promise as a rapid and accurate method for mapping chemicals over large areas.