Causes And Effects Of Airs Optics Temperature Cycles

In addition to the expected orbital thermal cycle, geophysical conditions with high thermal and reflected upwelling infrared (IR) drive measurable changes in the AIRS instrument with a period of 24 hours. Especially hot and bright scenes are important, with about 30% of the variability driven by thermal IR and 70% by reflected IR. We show how these cycles manifest in the instrument telemetry for temperatures and gain and with careful analysis can even be detected in spectral shifts.Thermal cycles are an unavoidable feature of instruments observing upwelling radiances from Earth, because the signal inherently carries varying amounts of energy into the instrument. Temperature control of the optical bench, on-board calibrator blackbody, and Focal Plane Array (FPA) in AIRS reduce the impacts of temperature variability to extremely small levels. This combined with good on-board telemetry of the temperatures and including temperature variability in our calibration algorithm has resulted in an instrument that achieves 'climate quality' measurements. Careful instrument and algorithm design allows us to characterize and document the impact of temperature variability and limit the effects to negligible levels, helping the instrument meet important climate-quality criteria specified in Ohring 2005.