Spectral influence analysis on sunshine duration measurement

Sunshine duration is an important variable in surface meteorological measurement. In this article, two methods for measuring sunshine duration are described, one is photovoltaic-based instrument, which ranges from 400 to 1100 nm, and the other is thermopile-based pyrheliometer, which ranges from 300 to 3000 nm. Due to the spectrum is more representative and accuracy for solar radiation, the pyrheliometer is recommended as the reference sensor for the detection of the threshold irradiance for defining the sunshine duration. The comparison between the photovoltaic- and thermopile-based instruments is carried out to uncover the spectral influence on sunshine duration measurement, analysis by the SMARTS tool is presented to calculate irradiance with different spectral ranges under different altitudes.