Abstract of my doctoral thesis Characterisation of FTS for Measurement of Stratospheric Trace Gases (University of Wales, Aberystwyth, 2000).
An investigation of the type and extent of errors in retrieved vertical profiles arising from common line shape defects is reported, and the results assessed with reference to the Bruker IFS 120M.
It is shown that variations in the size of the field stop within the manufacturing tolerances can give rise to significant artefactual subsidence, and the required accuracy of measurements of the instrument line shape has been quantified. The results of these simulations are considered with respect to the requirements of atmospheric models.
The development of a portable laser system for measuring instrument line shapes, simultaneously with the acquisition of atmospheric and low pressure cell spectra, is reported. Laser and hydrogen bromide spectra are presented along the results of attempts to fit the measured hydrogen bromide lines with simulations based on the laser measurements and on calculated instrument line shapes.
Laser system temperature and power data have been presented showing evidence of temperature drift in the laser cavity giving rise to frequency drift and mode hopping. These data are used to assess the frequency drift rate of the infrared laser and, hence, estimate the degree of asymmetry that might be expected in the measured laser line.
It is shown that a system such as this could, in theory, be used to provide valid simultaneous measurements of the instrument line shape of Fourier spectrometers and that the use of a low pressure gas cell provides a useful check on the laser measurement, however difficulties experienced in the use of the laser system led to a lack of reproducibility, and unacceptable asymmetry in the line shape measurements; these are discussed and suggestions for further work made.
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