2d Tomographic Reconstruction of Trace Gas Distributions from Long-path DOAS Measurements: General Approach, Validation and Outlook on an Experiment on an Urban Site

* Corresponding author: [email protected] Abstract – DOAS-tomography is a remote sensing technique to retrieve 2 or 3 dimensional distributions of atmospheric trace gas concentrations. It combines Differential Optical Absorption Spectroscopy yielding average concentrations of trace gases along long light paths with reconstruction methods from computerised tomography. Here we refer to reconstructions from ground based measurements using artificial light sources. We present our reconstruction method, consisting in a discrete approach, and show that for locally confined distributions like dispersions plumes, reconstruction quality and reconstructed total concentrations can be tremendously improved by choosing an optimal parametrisation in terms of basis functions and dimension of the discretisation grid. Choice of the light path geometry has large influence as well, where for constant number of light paths, increasing the number of emitting systems tends to improve reconstructions. The method is applied to data from an indoor measurement and results are in good agreement with expectations, while the impact of measurement errors is moderate. This method will be applied to an experiment intended to measure cross sections of trace gas distributions over the city centre of Heidelberg, Germany, taking place in spring and summer 2005.