Determination of Optimized Microwindows for Analysis of Absorption Spectra From Ground- based FTIR Spectrometer

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Addis Ababa University


In infrared remote sensing by Fourier transform spectroscopy usually not the measured spectrum as a whole is analysed hut subsets, so-called "microwindows", which contain prominent transitions of the target species. While microwindows noted in the literature were selected by conventional methods, the purpose of this work is to select optimum microwindows for analysis of target species such that the related retrieval error is minimized. The choice of microwindows is shown to depend on the assumed retrieval scenario. In particular microwindow boundaries and associated retrieval errors are sensitive to assumptions on errors of parameters which are not jointly fitted along with the target parameters but kept constant during the retrieval. It is shown that consideration of uncertainities in pressure, temperature and measurement geometry has major influence on the optimization of microwindow boundaries and the selection of microwindows. Some of the microwindows which are optimum in the idealized case of negligible uncertainties of pressure, temperature and measurement geometry, are similar to those reported in the li terature, while there are considerable differences between the latter and those microwindows optimized for more realistic conditions. Hence our anal ysis suggests that existing microwindows defined by conventional methods are not best suitable for application to realistic measurement scenarios because these sources of systematic errors have been underestimated



Determination of Optimized Microwindows