Experimental evaluation of a radial beam geometry for mapping air pollutants using optical remote sensing and computed tomography

We describe the first experimental evaluation of a non-overlapping radial b eam geometry to map air pollutants using computed tomography (CT) and optic al remote sensing (ORS) instruments. Nitrous oxide was released from a poin t source inside a 11 m long x 5.4 m wide ventilation chamber. An open path Fourier transform infrared (OP-FTIR) spectrometer gathered path integrated concentration data. The smooth basis function minimization (SBMF) CT algori thm was applied to a radial geometry with 19 rays. Two-dimensional maps wer e reconstructed from the OP-FTIR measurements and compared with kriged maps calculated from 13-point samples collected simultaneously during the exper iments. The CT reconstructions showed good agreement compared to the kriged maps obtained from point samples (concordance correlation factor > 0.55). The CT reconstructions also located the peak concentration within 1.2 m com pared to the point samplers. In contrast to the complex CT beam geometries proposed in the past, the development of this radial scanning configuration could broaden the application of CT to many optical remote sensing instrum ents. (C) 1999 Elsevier Science Ltd. All rights reserved.