Imaging Indoor Tracer-Gas Concentrations with Computed Tomography: Experimental Results with a Remote Sensing FTIR System

Yost, Michael G.; Gadgil, A.J.; Drescher, Anushka C.; Zhou, Yang; Simonds, M.A.; Levine, Simon P.; Nazaroff, WW; Saisan, P.A.

doi:10.1202/0002-8894(1994)055<0395:iitcwc>2.0.co;2

Cited by 9 publications

(16 citation statements)

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“…In comparison point sampling techniques can only give local details of the concentration maps and conclusions to larger scales may be falsified by small scale fluctuations. Tomographic lineintegrating measurement techniques for trace gases were proposed by Wolfe (1980) and first indoor measurements were realized by Yost et al (1994) using open-path Fourier infrared absorption spectroscopy. Since then there have been improvements in speed and spatial resolution (e.g.…”

Section: Introductionmentioning

confidence: 99%

Longpath DOAS tomography on a motorway exhaust gas plume: numerical studies and application to data from the BAB II campaign

et al. 2004

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Abstract. This paper presents a procedure for performing and optimizing inversions for DOAS tomography and its application to measurement data. DOAS tomography is a new technique to determine 2-and 3-dimensional concentration fields of air pollutants or other trace gases by combining differential optical absorption spectroscopy (DOAS) with tomographic inversion techniques. Due to the limited amount of measured data, the resulting concentration fields are sensitive to the inversion process. Therefore detailed error estimations are needed to determine the quality of the reconstruction. In this paper we compare different row acting methods for the inversion, present a procedure for optimizing the parameters of the reconstruction process and propose a way to estimate the error-fields by numerical studies. The procedure was applied to data from the motorway emission campaign BAB II. Two dimensional NO 2 cross sections at right angles to the motorway could be reconstructed qualitatively well at different meteorological situations. Additionally we present error fields for the reconstructions which show the problems and skills of the used measurement setup. Numerical studies on an improved setup for future motorway campaigns show, that DOAS tomography is able to produce high quality concentration maps.

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Section: Introductionmentioning

confidence: 99%

Longpath DOAS tomography on a motorway exhaust gas plume: numerical studies and application to data from the BAB II campaign

et al. 2004

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“…The theory and concepts of computed tomography have been discussed, 4,5 and experimental trials relevant to occupational or indoor air monitoring applications recently were reported. 6 Certain practical limitations arise in applying CT to indoor air or environmental monitoring. CT requires input…”

Section: Discussionmentioning

confidence: 99%

Evaluation of Virtual Source Beam Configurations for Rapid Tomographic Reconstruction of Gas and Vapor Concentrations in Workplaces

Park

Yost

Levine

1997

Journal of the Air & Waste Management Association

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Beam path average data from an Open Path Fourier Transform Infrared (OP-FTIR) spectrometer can be used to reconstruct two-dimensional concentration maps of the gas and vapor contaminants in workplaces and the environment using computed tomographic (CT) techniques. However, a practical limitation arises because in the past, multiple-source and detector units were required to produce a sufficient number of intersecting beam paths in order to reconstruct concentration maps. Such a system can be applied to actual field monitoring situations only with great expense and difficulty. A single monostatic OP-FTIR system capable of rapid beam movement can eliminate this deficiency. Instead of many source and detector units, a virtual source arrangement has been proposed using a number of flat mirrors and retroreflectors to obtain intersecting folded beam paths.Three virtual source beam configurations generated for a single-beam steerable FTIR system were tested using 54 flat mirrors and four retroreflectors or 54 flat mirrors and 56 retroreflectors mounted along the perimeter walls of a typical 24-x 21-ft test room. The virtual source CT configurations were numerically evaluated using concentration maps created from tracer gas concentration distributions measured experimentally in a test chamber. Synthetic beam path integral data were calculated from the test maps and beam configurations. Computer simulations of different beam configurations were used to determine the effects of beam geometry. The effects of noise and peak-reducing artifacts were evaluated. The performance of the tomographic reconstruction strategy was tested as a function of concentration and concentration gradients.

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“…[1][2][3][4][5][6] The potential advantages of this technique have been extensively discussed in the literature. 3,[7][8][9][10][11] In early papers on the subject, CT methods were conceptually shown to have the potential for good reconstruction of air pollutant concentrations in a plane under certain narrowly limited conditions. [3][4][5][6] Recently, experiments by our group have successfully demonstrated CT reconstructions in a room-sized chamber.…”

Section: Introductionmentioning

confidence: 99%

“…[3][4][5][6] Recently, experiments by our group have successfully demonstrated CT reconstructions in a room-sized chamber. [8][9][10] The first experimental study on the CT reconstruction of indoor air concentrations, coupled with open-path Fourier transform infrared (OP-FTIR) spectrometers, was reported by Yost et al 8 The experiments were conducted with the use of a single bi-static OP-FTIR. Thus, the source and detector had to be moved substantially to get the desired sets of parallel rays.…”

Section: Introductionmentioning

confidence: 99%

Tomographic Reconstruction of Tracer Gas Concentration Profiles in a Room with the Use of a Single OP-FTIR and Two Iterative Algorithms: ART and PWLS

Park

Fessler

Yost

et al. 2000

Journal of the Air & Waste Management Association

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Computed tomographic (CT) reconstructions of air contaminant concentration fields were conducted in a roomsized chamber employing a single open-path Fourier transform infrared (OP-FTIR) instrument and a combination of 52 flat mirrors and 4 retroreflectors. A total of 56 beam path data were repeatedly collected for around 1 hr while maintaining a stable concentration gradient. The plane of the room was divided into 195 pixels (13 × 15) for reconstruction.The algebraic reconstruction technique (ART) failed to reconstruct the original concentration gradient patterns for most cases. These poor results were caused by the "highly underdetermined condition" in which the IMPLICATIONS Gas concentration mapping in a room-sized chamber with the use of CT techniques, coupled with OP-FTIR, demonstrates that this system and reconstruction method could be directly applied in many environmental and industrial settings. The experimental beam configuration was in the highly underdetermined condition, which is commonly encountered in most conceivable fields. A new CT algorithm, the PWLS, was applied to remedy this unfavorable condition, since the standard ART algorithm results in poor CT reconstructions. Generally, concentration gradient patterns and peak locations were successfully reproduced. This system is the first experimental verification for the practical application of a CT system for real air pollutant mapping.number of unknown values (156 pixels) exceeds that of known data (56 path integral concentrations) in the experimental setting. A new CT algorithm, called the penalized weighted least-squares (PWLS), was applied to remedy this condition. The peak locations were correctly positioned in the PWLS-CT reconstructions. A notable feature of the PWLS-CT reconstructions was a significant reduction of highly irregular noise peaks found in the ART-CT reconstructions. However, the peak heights were slightly reduced in the PWLS-CT reconstructions due to the nature of the PWLS algorithm. PWLS could converge on the original concentration gradient even when a fairly high error was embedded into some experimentally measured path integral concentrations.It was also found in the simulation tests that the PWLS algorithm was very robust with respect to random errors in the path integral concentrations. This beam geometry and the use of a single OP-FTIR scanning system, in combination with the PWLS algorithm, is a system applicable to both environmental and industrial settings.

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Imaging Indoor Tracer-Gas Concentrations with Computed Tomography: Experimental Results with a Remote Sensing FTIR System

Cited by 9 publications

References 0 publications

Longpath DOAS tomography on a motorway exhaust gas plume: numerical studies and application to data from the BAB II campaign

Longpath DOAS tomography on a motorway exhaust gas plume: numerical studies and application to data from the BAB II campaign

Evaluation of Virtual Source Beam Configurations for Rapid Tomographic Reconstruction of Gas and Vapor Concentrations in Workplaces

Tomographic Reconstruction of Tracer Gas Concentration Profiles in a Room with the Use of a Single OP-FTIR and Two Iterative Algorithms: ART and PWLS

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