28 December 1999 Experimental and theoretical study of uncertainty in pyranometers for surface radiation
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Abstract
The Eppley pyranometer is widely used to measure shortwave irradiances. This instrument consists of a blackened surface in intimate thermal contact with the hot junction of a thermopile. The cold junction of the thermopile is in thermal contact with a heat sink. Shortwave radiation transmitted through two concentric hemispherical domes is absorbed by the blackened surface. The voltage developed by the thermopile is then interpreted in terms of the shortwave irradiance. Measurements obtained using these instruments are known to be influenced by thermal radiation that produces an offset from the signal that would result solely from the incident shortwave radiation. The thermal radiation emitted and reflected by the filters modifies the net radiation at the detector surface. The ongoing efforts to model these exchanges and to use experimental results to verify the model are described. The parallel experimental effort consists of determining the sensitivity of instrument response to thermal radiation effects. In this effort, thermistors are used to characterize the thermal gradients responsible for the instrument offset. The ultimate goal of the work described is to provide reliable protocols, based on an appropriate instrument model, for correcting measured SW irradiance for variable thermal radiation effects.
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Amie M. Smith Nester, Martial P.A. Haeffelin, Felix J. Nevarez, J. Robert Mahan, Seiji Kato, Kendall Rutledge, "Experimental and theoretical study of uncertainty in pyranometers for surface radiation", Proc. SPIE 3870, Sensors, Systems, and Next-Generation Satellites III, (28 December 1999); doi: 10.1117/12.373182; https://doi.org/10.1117/12.373182
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