The use of transfer radiometers in validating the visible to shortwave infrared calibrations of radiance sources used by instruments in NASA's Earth Observing System

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The quantitative study of climate change over decades requires successive generations of satellite, airborne and ground-based instrumentation carefully calibrated against a common radiance scale. In NASA's Earth Observing System (EOS) program, the most common sources used in the laboratory radiance calibration of satellite, ground-based and airborne instruments operating in the reflective solar wavelength region of 400–2500 nm are integrating spheres and diffuse reflectance panels illuminated by irradiance standard lamps. Since 1995, the EOS calibration program operating within NASA's EOS Project Science Office (PSO) has enlisted the expertise of the National Institute of Standards and Technology (NIST), the University of Arizona Optical Sciences Center's Remote Sensing Group (UA), Japan's National Research Laboratory of Metrology (NRLM) and NASA's Goddard Space Flight Center (GSFC) in an effort to validate the radiance scales assigned to sources used in the prelaunch calibration of EOS instruments and to critically examine the operation, repeatability and stability of those sources. Radiance scale validation is accomplished using stable transfer radiometers operating at visible to shortwave infrared wavelengths and calibrated and characterized by each institution using a variety of techniques. In the 10 comparisons performed since February 1995, the agreement between the radiance measurements of these transfer radiometers is ±1.80% at 411 nm, ±1.31% at 552.5 nm, ±1.32% at 868.0 nm, ±2.54% at 1622 nm, and ±2.81% at 2200 nm (σ = 1).