Using deep convective clouds identified in 16 years of AIRS infrared data for the absolute calibration and stability evaluation of the AIRS 0.4 to 1.0 micron reflected light channels

摘要

In principle, extreme Deep Convective Clouds (DCC) should be perfect Lambertian diffusers of solar reflected radiation. As such they can be used for the calibration of reflected light channels. We use DCC identified with a thermal infrared channels of the Atmospheric Infrared Sounder (AIRS) to evaluate the usefulness of DCC for the calibration AIRS visible light channels. The DCC signal in the reflected light channels approaches the signal expected from a perfect diffuser in only a small portion of the 13 km AIRS thermal IR and 2 km AIRS reflected light channels. This limits the absolute calibration accuracy derivable from DCC to the 5% level, but still allows trend measurements at the smaller than 0.01%/yr level. This technique allows us to estimate the trend in the globally Reflected ShortWave radiation (RSW) as +0.003%/yr with 0.009%/yr one sigma uncertainty. Trends at this level are significant from a climate perspective.