An improved aircraft underflight instrument for the derivation of band gains in satellite sensors

There is an increasing need for improved in-flight calibration of visible and near-IR satellite sensors to gather reliable information on global climate mechanisms and climate change. Satellite instruments for the near future, such as MODIS and SeaWiFS, require accurate calibration throughout their lifetimes on orbit, and represent a challenging task. Flying a calibrated transfer spectroradiometer on a high altitude aircraft above most of the atmosphere over a uniform and extended radiance target near the subsatellite track during satellite overpass provides the most direct method of independently calibrating satellite sensors. The “High Altitude Underflights to Calibrate Satellite Sensors” (HAUCSS) system, developed by NOAA and NASA under various acronyms since 1980, is described here with emphasis on improvements in the system, along with an outline of the satellite instrument calibration method, performance, uncertainty analysis and planned improvements. The HAUCSS system has been used to underfly the GOES-8 imager and NOAA-14 AVHRR sensors. An in-flight radiance calibration source is expected to be used in the future. Future plans also include real time ground station links through an aircraft-TDRSS link for instrument control from ground and real time data viewing