Optimal Measurement of Surface Shortwave Irradiance Using Current Instrumentation

Although most measurements of total downwelling shortwave irradiance are made with pyranometrrs, the World Climate Research Program's Baseline Surface Radiation Network has recommended the use of the summation of shortwave components in which the direct normal irradiance is measured and multiplied by the cosine of the solar zenith angle and then added to the diffuse horizontal irradiance measured by a pyranometer that is shaded from direct solar radiation by a disk.