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Passive Fourier Transform Infrared (FT-IR) is a widely employed technique for the remote sensing of target vapors, including clouds, plumes and fugitive emissions. Prior to any qualitative or quantitative analysis of passive FT-IR data, it is essential to ensure that the instrument has been radiometrically calibrated. This process converts the instrument's detection signal spectrum into an equivalent radiation intensity spectrum. However, the measurement spectrum can be distorted due to inherent characteristics of the instrument or environmental variations during the measurement process. Furthermore, there has been a paucity of discourse and analysis concerning the verification of the measurement spectrum. In this paper, the instrument response matrix is employed for the purposes of spectral verification and radiometric calibration. The matrix is constituted of three columns: the spectral intensity maximum value and corresponding wavenumber, as well as the temperature. The initial and subsequent parameters are indicative of the spectra, and experimental data indicates that they are functions of the blackbody temperature. The instrument response matrix is a valuable tool for determining the range of the corresponding blackbody temperature and for assessing the adequacy of the measured intensity. The spectrum was measured at different temperatures within the range of 300K to 600K, and then the instrument response matrix was created through data processing. The following example illustrates the application of the instrument response matrix for the purposes of spectral validation and radiometric correction.
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