Comparison of Plotting Methods for Solar Radiometer Calibration

An alternative formulation of the Langley plot relating observed solar irradiance, extraterrestrial solar irradiance, and air mass has been suggested to potentially improve radiometer calibration accuracy. In this study, results from the traditional and alternative plotting methods are compared using both simulated and measured data. The simulations indicate that their relative accuracies depend on the time scale of the atmospheric extinction fluctuations. The two methods are found to be essentially equivalent with the measured data. Ground-based solar radiometry provides much of our fundamental knowledge about the optical and physical properties of both the sun and the earth’s atmosphere (Shaw 1982; Holben et al. 1998; McArthur et al. 2003). Analysis of the data involves combining measurements of the sensor signal I( ) at different wavelengths through a range of airmass values M in order to infer the extraterrestrial solar irradiance signal I0( ) and the atmospheric extinction coefficient k( ) using the Beer–Lambert–Bouger equation: