20 years of Atmospheric Infrared Sounder (AIRS) data: spectral calibration (Conference Presentation)

A key parameter of the AIRS spectral calibration is the position of the detector arrays in the focal plane, Yo. Given Yo, the centroid of the spectral response function for each AIRS channel is give by the grating model. A 1µm shift of Yo corresponds to a 1% shift of the centroid of the spectral response functions. Spectral shift at the 0.02µm level are readily detectable. The amplitude of seasonal and diurnal shifts in Yo is about 0.5 µm. Between 2002 and 2024 Yo stayed within 1 µm of −13 µm. This is a tribute to the fact that the AIRS spectrometer and the focal plane are actively temperature controlled. Real-time users are not likely to notice the radiometric effect of a 1 µm variation of the spectral calibration in the presence of other noise and natural variability. However, if left uncorrected changes as small as 1 µm can create false trends in a time series analysis which may interfere with the detection of true climate change signals. Given the spectral calibration, the AIRS data can be presented on a fixed spectral sampling grid. This data is available as the AIRS L1c v6.7 product. An L1c V8 product with consistent processing for 20 years is under development.