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Accurate measurements of solar radiation require regular recalibration of the radiometers used to make the irradiance measurement. NREL has developed the Broadband Outdoor Radiometer Calibration (BORCAL) approach for the annual calibration of pyranometers, pyrheliometers, and pyrgeometers used by the Department of Energy. BORCALs are conducted at the Solar Radiation Research Laboratory (SRRL) and at the Atmospheric Radiation Measurement (ARM) Program's Southern Great Plains (SGP) Radiometer Calibration Facility. These calibrations are traceable to the World Radiometric Reference (WRR) and to the World Infrared Standard Group (WISG).

BORCAL results are determined from the individual radiometer's output signal (microvolts, DC) and the coincident reference irradiance (Watts per sq meter) as measured by reference radiometer(s). The radiometer responsivity (microvolts per Watt per sq meter) is determined by BORCAL methods.

Historical values of responsivities for groups of radiometers are available from past BORCAL Reports and are also available for individual instruments through the ARM Instrument Management (AIM) database. The reference irradiance data from each BORCAL event are also available below in ASCII text format.


(0.5~6 MB PDF Document)

(10~250 KB ASCII Text)

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(10~40 MB PDF Document)

(50~300 KB ASCII Text)

[1] Reda, I.; Hickey, J.; Long, C.; Myers, D.; Stoffel, T.; Wilcox, S.; Michalsky, J. J.; Dutton, E. G.; Nelson, D. (2005). "Using a Blackbody to Calculate Net Longwave Responsivity of Shortwave Solar Pyranometers to Correct for Their Thermal Offset Error During Outdoor Calibration Using the Component Sum Method." Journal of Atmospheric and Oceanic Technology. , 2005; pp. 1531-1540; NREL Report No. JA-560-36646. doi:10.1175/JTECH1782.1
[2] Reda, I.; Myers, D.; Stoffel, T. (2008). "Uncertainty Estimate for the Outdoor Calibration of Solar Pyranometers: A Metrologist Perspective." Measure. (NCSLI Journal of Measurement Science). Vol. 3(4), December 2008; pp. 58-66; NREL Report No. JA-581-4137
[3] Reda, I.; Andreas, A. (2004). "Solar Position Algorithm for Solar Radiation Applications." Solar Energy. Vol. 76(5), 2004; pp. 577-589; NREL Report No. JA-560-35518. doi:10.1016/j.solener.2003.12.003
[4] Stoffel, T.; Reda, I. (2009). "NREL Pyrheliometer Comparisons: 22 September - 3 October 2008 (NPC-2008)." 54 pp.; NREL Report No. TP-550-45016.
[5] Reda, I.; Stoffel, T.; Myers, D. (2003). "Method to Calibrate a Solar Pyranometer for Measuring Reference Diffuse Irradiance." Solar Energy. Vol. 74, 2003; pp. 103-112; NREL Report No. JA-560-35025. doi:10.1016/S0038-092X(03)00124-5
[6] Reda, I. (1996). Calibration of a Solar Absolute Cavity Radiometer with Traceability to the World Radiometric Reference. 79 pp.; NREL Report No. TP-463-20619.
[7] Reda, I.; Gröbner, J.; Stoffel, T.; Myers, D.; Forgan, B. (2008). Improvements in the Blackbody Calibration of Pyrgeometers. ARM 2008 Science Team Meeting (Poster).
[8] Reda, I.; Stoffel, T. (2010). Pyrgeometer Calibration for DOE-Atmospheric System Research Program using NREL Method (Presentation). 9 pp.; NREL Report No. PR-3B0-47756;

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