Radiometric stability in 16 years of AIRS hyperspectral infrared data

摘要

With global warming at the rate of 10 mK/yr, it is important to carefully characterize instrument related trends, if the AIRS data are used for climate change research. We evaluated the stability of the AIRS Level 1B version 5 calibration for seven atmospheric window channels between 2002 and 2018 under clear ocean clear conditions. We do this by analyzing the trend in the difference between the observed brightness temperatures and those calculated based on the daily Sea Surface Temperature product provided by NOAA. Trends for the 961, 1128 and 1231 cm~(-1) channels are close to +3 mK/yr, at 790 and 901 cm~(-1) the trends are 6 mK/yr. For all observation the AIRS window channels read increasingly warmer. The observed trends are day/night consistent and insensitive to changes in the clear filter. The effects of scattering due to scan mirror contamination are evident at 2508 and 2616 cm~(-1) for extremely cold scenes surrounded by warm scenes, but scattering does not produces the observed warming trends for warm scenes. It is possible that much of the observed warming in the AIRS window channels is due to a shift in the day/night and skin effect corrections, which was not accounted for in our analysis. This would be a new geophysical effect related to the warming of the oceans, which requires more careful evaluation.