23 May 1997 Calibration of a high-resolution open-path FTIR spectrometer combined with an adjustable 100-m multipass cell
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Abstract
The substantiation of the characteristics, which make the Open-Path FTIR technique attractive for monitoring the ambient air quality, is the aim of a validation program, which is realized at the Fachhochschule Duesseldorf. Part of this validation program are calibration measurement, which are important to determine the performance characteristics of a remote FTIR system. The measurements are carried out at the official calibration laboratory of the Environmental State Agency of Northrhine Westphalia and at the Laboratory for Environmental Measurement Techniques at the Fachhochschule Duesseldorf, using a high resolution Open- Path FTIR spectrometer combined with an adjustable gas cell from 7 to 110 meters. The calibrations were done for methane in a concentration range from 20 to 10000 ppm.m and are evaluated corresponding to the standardization documents which are currently used to determine the performance characteristics of continuous measurement systems. It turned out that the calculated calibration function for methane is nonlinear when analyzing by the classical least square algorithm. Furthermore, if using a nonlinear calibration function over the whole concentration range, the correction of measured concentrations and the calculation of the lower detection limits leads to unrealistic high values. Better results were achieved by separating the whole concentration range in a linear one at low concentrations and a nonlinear one at high concentrations in order to determine the characteristics of the used remote FTIR system.
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Alexander Ropertz, Torsten Lamp, Mathilde Douard, Konradin Weber, Andrea Gaertner, C. Elbers, R. Nitz, "Calibration of a high-resolution open-path FTIR spectrometer combined with an adjustable 100-m multipass cell", Proc. SPIE 3107, Remote Sensing of Vegetation and Water, and Standardization of Remote Sensing Methods, (23 May 1997); doi: 10.1117/12.274749; https://doi.org/10.1117/12.274749
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