The NOAA Science Advisory Board’s Panel on Strategies for Climate Monitoring prioritizes the development of a set of Benchmark measurements for monitoring long-term changes in climate. As defined by the Panel, Benchmark measurements adhere to principles requiring demonstrable accuracy tied to metrological standards on a limited set of climate variables which are of great relevance to decadal-to-century scale climate change. An illustrative example of a Benchmark measurement is the baseline CO₂ monitoring effort maintained by CMDL. Spectrally resolved, thermal radiance measurements from space constitute a key Benchmark measurement that is well-studied (Harries 2001) and capable of early deployment. The realization of this benchmark measurement requires scientific infrastructure which is singularly focused on the radiometric accuracy target. This infrastructure connects precision measurements in the laboratory through identical hardware to on-orbit diagnostics in the satellite.

We present a characterization of the systematic error sources of a prototype for a low-cost, lightweight satellite designed to meet the Benchmark requirements for radiance measurements. The prototype includes two bore-sighted Michelson interferometers covering the spectral window from 250 to 2000 cm^-1 (40 to 5 microns) at a spectral resolution of ~ 0.5 cm^-1, with an accuracy goal of 0.1 K on at 250 K brightness temperature at 750 cm^-1. This level of accuracy in a space-based measurement represents a significant challenge. Because the satellite must satisfy the objective of convincing future investigators of accuracy, radiometric performance must be clearly documented. Individual sources of systematic error are evaluated and their contributions to radiometric accuracy at the level of 0.1 K are calculated. Errors related to the calibration standards (blackbodies) and instrumental optical performance are treated, including blackbody thermometry and emissivity, out of field of view optical sensitivity, infrared detector and signal chain nonlinearity, and polarization effects. These errors are treated with the goal of providing a performance baseline for critical analysis of on-orbit accuracy and to evaluate effects of the space environment on the measurement calibration.