Determination of Optimized Microwindows for Analysis of Absorption Spectra From Ground- based FTIR Spectrometer
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Date
1998-06
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Addis Ababa University
Abstract
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
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Determination of Optimized Microwindows