In a recent commentary paper, Whiteman et al. [Appl. Opt. 50, 2170 (2011)] discussed the applicability of the hybrid calibration method described by Leblanc and McDermid [Appl. Opt. 47, 5592 (2008)] under certain circumstances. They propose to use multiple lamps or a scanning lamp instead of a single lamp at a fixed location, to improve this method. The revised method proposed by Whiteman et al. indeed improves the spatial characterization of the receiver illumination, but still does not reproduce the ideal case of an illumination configuration similar to that of the atmospheric water vapor measurement. Its implementation also increases the chances for system disruption and can potentially defeat the purpose of the method described in Leblanc and McDermid, namely, long-term stability.
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