Effects of Solar Radiation on the Performance of Pyrgeometers with Silicon Domes

Abstract

The performance of the Eppley pyrgeometer with a silicon dome presents several anomalies during daytime measurements. These problems are related mainly to the solar heating of the dome, which causes nearly instantaneous fluctuations, about ±1%–2% from the average value, in the longwave irradiance measured by the pyrgeometer during cloudless days. An evaluation of the solar heating effect of the dome made with a set of sun and shade experiments indicates that the pyrgeometer output includes an equivalent of about 3.6% of the incoming solar radiation. In spite of the improvement with the use of silicon instead of KRS-5 domes, the error due to solar heating requires some kind of correction. Sun and shade experiments under a number of wind speed conditions are used to derive an empirical correction that is based on the global solar radiation. Abstract The performance of the Eppley pyrgeometer with a silicon dome presents several anomalies during daytime measurements. These problems are related mainly to the solar heating of the dome, which causes nearly instantaneous fluctuations, about ±1%–2% from the average value, in the longwave irradiance measured by the pyrgeometer during cloudless days. An evaluation of the solar heating effect of the dome made with a set of sun and shade experiments indicates that the pyrgeometer output includes an equivalent of about 3.6% of the incoming solar radiation. In spite of the improvement with the use of silicon instead of KRS-5 domes, the error due to solar heating requires some kind of correction. Sun and shade experiments under a number of wind speed conditions are used to derive an empirical correction that is based on the global solar radiation.