NASA - National Aeronautics and Space Administration

In using pyranometers to measure solar irradiance, it is important to know the magnitudes and the consequences of the thermal effect, which is introduced by the glass domes of the instruments. Historically, the thermal dome effect was not monitored on a regular basis. Case studies show that, due to the thermal dome effect, the output of the pyranometers altered from less than 5 W m⫺2 in the nighttime to over 20 W m⫺2 around noontime during the Aerosol Recirculation and Rainfall Experiment (ARREX) in 1999 and the Southern African Fire–Atmosphere Research Initiative (SAFARI) in 2000 field campaigns, depending on sky conditions. A calibration and data processing procedure with the thermal dome effect incorporated has been tested to resolve the issue. It is demonstrated that the intrinsic calibration constants of the pyranometers can be obtained if two pyranometers are used side by side, and the thermal dome effect may be inferred whenever a pyranometer and a pyrgeometer are collocated.