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) 12
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.
