Calibration of a Fourier transform spectrometer using its internal lamp as a reference source

摘要

Spectral radiance responsivity calibration of Fourier transform spectrometers (FTSs) used for solar radiance observations is important for removing systematic errors resulting from the different spectral responsivities of each instrument. In this study, the spectral responsivity of an FTS with a Globar lamp as an internal light source was calibrated, and its temperatures were determined without direct temperature measurement through nonlinear fitting using a modified three-temperature method (referred to hereafter as m-TTM). Our calibration results were verified using a standard tungsten strip lamp. Furthermore, the spectral radiance results obtained with three different apertures proved that the FTS radiance has a systematic error of approximately 5%, deviating from that of the standard strip lamp owing to an assumption of a perfect emissivity. In particular, the real emissivity of the Globar lamp, for which the value still includes an instrumental optical error, in the range of 4000 cm(-1) to 8000 cm(-1) (for the InSb detector) was found to be approximately 0.94-0.98 after correction by a supplementary measurement using a certified standard strip lamp as an external light source. The deviations of the results for all the apertures were less than +/- 1%. Therefore, this study showed that the accurate responsivity calibration of an FTS with an internal light source such as a Globar lamp could be obtained by employing the m-TTM.