Selection of a solar reference spectrum for GLI’s reflective bands

For remote sensing of the Earth in the ultraviolet (UV), visible (VIS) and short-wave infrared (SWIR), the extraterrestrial solar spectral irradiance (Esun (λ)) has to be known with high accuracy. However, the discrepancy in currently available zero air mass Esun (λ) data is large due to two sources of uncertainties: the variation of the solar activity and uncertainties in the experimental data. NASDA’s global orientated GLI sensor will be launched in 2002, hence it became necessary to select a solar spectrum which is suitable for GLI’s reflective channels in terms of spectral coverage, total error etc. This is why a study was performed at NASDA, EORC to select a solar irradiance spectrum by comparing various spectra weighted by the spectral response functions of GLI’s reflective channels. As a result the experimental solar irradiance data published by Thuillier in 2001 were selected because this data seems to have the so far smallest error (RMS error in VIS: 1.5 2%), a suitable spectral range and resolution for GLI’s reflective channels (200–2500 nm) and ∆λ = 1 nm (200–870nm) and 20 nm (870–2500nm).