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Uncertainty in terrestrial solar radiation measurements of a few watts per square metre (1 W/m2 to 2 W/m2) is needed to validate estimates of the Earth's radiation balance derived from satellite data. The characterization of solar energy resources for renewable energy technologies requires similar accuracy for economical technology deployment. Solar radiation measurement research at the National Renewable Energy Laboratory addresses calibrations, operational characteristics, and corrections for terrestrial solar radiation measurements. The characterization of field instrument geometric and thermal responses contributing to radiometric errors is described, together with correction schemes reducing the uncertainty of broadband irradiance measurements from tens of watts per square metre to a few (±2 W/m2 to ±5 W/m2). Such improvements in accuracy reduce the time and labour required for detecting and quantifying trends in terrestrial solar radiation and possible changes in the Earth's radiation budget.
Stoffel et al. (Sun,) studied this question.