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 beam geometry to map air pollutants using computed tomography (CT) and optical remote sensing (ORS) instruments. Nitrous oxide was released from a point source inside a 11 m long×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 algorithm was applied to a radial geometry with 19 rays. Two-dimensional maps were reconstructed from the OP-FTIR measurements and compared with kriged maps calculated from 13-point samples collected simultaneously during the experiments. 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 compared 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 instruments.