Reducing Broadband Shortwave Radiometer Calibration-Bias Caused by Longwave Irradiance in the Reference Direct Beam
Authors
Mike Dooraghi — National Renewable Energy Laboratory
Manajit Sengupta — National Renewable Energy Laboratory
Mark Carl Kutchenreiter — National Renewable Energy Laboratory
Ibrahim Reda — National Renewable Energy Laboratory
Afshin Michael Andreas — National Renewable Energy Laboratory
Aron Habte — National Renewable Energy Laboratory
Description
Shortwave radiometers such as pyranometers, pyrheliometers, and photovoltaic cells are calibrated with traceability to consensus reference, maintained by Absolute Cavity Radiometers (ACRs). The ACR is an open cavity with no window that measures the extended broadband spectrum of the terrestrial direct solar beam irradiance, unlike shortwave radiometers that cover a limited range of the spectrum. The difference be-tween the two spectral ranges may lead to calibration bias that can exceed 1%. This poster describes a method to reduce the calibration bias resulting from using broadband ACRs to calibrate shortwave radiometers by using an ACR with Schott glass window to measure the reference broadband shortwave irradiance in the terrestrial direct solar beam from 0.3 µm to 3 µm. Reducing the calibration bias will result in lowering the historical solar irradiance by at least 0.9%. The published results in this article might raise the awareness of the calibration discrepancy to the users of such radiometers, and open a discussion within the solar and atmospheric science community to define their expectation from such radiometers to the radiometers’ manufacturers and calibration providers.
