Infrared tomographic system for monitoring the two-dimensional distribution of atmospheric pollution over limited areas

The authors analyze the feasibility and performance of a particular tomographic system for atmospheric pollution monitoring over limited areas (e.g. urban areas). Such a system exploits attenuation-based infrared measurements of the average concentration of the fundamental molecular species of pollutants along rectilinear paths. First, the paper demonstrates the feasibility of an apparatus based on semiconductor infrared laser diode transmitters and passive retroreflectors, capable of measuring the average concentration of pollutants along rectilinear paths with 2 km maximum length, by exploiting their infrared absorption properties. For each gaseous species of interest, the optimal wavelength is then singled out, with the purpose of applying the derivative method for measuring the corresponding average atmospheric concentration. The optimal wavelengths are determined based on both absorption data of atmospheric components and plausible ranges of variation of their concentration. Finally, the authors present simulations carried out to evaluate the reconstruction of spatial concentration fields of several air pollutants, obtained through a tomographic inversion algorithm exploiting simultaneous attenuation measurements made along different infrared links. Two different network topologies for such measurements are considered