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Absolute Cavity Pyrgeometer
by Dr. Ibrahim Reda


The Absolute Cavity Pyrgeometer (ACP) is developed by the National Renewable Energy Laboratory used to measure absolute atmospheric longwave irradiance and functions as a reference instrument for the calibration of pyrgeometers traceable to the International System of Units (SI). It allows the user to perform calibrations and measure irradiance with an uncertainty estimate of ± 1.5%, far less uncertainty than can be achieved with blackbody values which produce errors from spectral mismatch. The ACP might be used to more accurately calibrate instruments used in outdoor longwave irradiance metrology, atmospheric science, deployment of renewable energy technologies, agriculture, IR thermometry, night vision and guidance systems. The ACP has been compared with the InfraRed Integrating Sphere (IRIS) six times, IRIS is developed by the World Radiation Center (WRC) and the difference between the measured irradiance by ACP and IRIS has been within +/- 2 W/m2, based on the comparisons results the ACP and IRIS would establish the world reference for measuring the atmospheric longwave irradiance.


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Topic : Theme 1: Earth Energy Balance.
Reference : T1-C22

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