Solar Radiation Research Laboratory

Broadband Outdoor Radiometer Calibrations

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) 1 2 approach for the annual calibration of pyranometers and pyrheliometers 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 3 and to the National Institute of Standards and Technology.4

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)

    ARM Logo

(10~40 MB PDF Document)

(50~300 KB ASCII Text)


1. D.R. Myers, I. Reda, S. Wilcox, and A. Andreas, 2004, "Optical Radiation Measurements for Photovoltaic Applications: Instrument Uncertainty and Performance." NREL Conference Paper NREL/CP-560-36320, 12 pages, August 2004. Download: 983 KB PDF Document.

2. D.R. Myers, T.L. Stoffel, I. Reda, S.M. Wilcox, and A. Andreas, 2002, "Recent Progress in Reducing the Uncertainty in and Improving Pyranometer Calibrations." Transactions of the ASME, Vol 124, pp 44-49, February 2002. Download: 766 KB PDF Document.

3. World Radiation Center:

4. NIST:

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