The Infrared Solar Spectrum Measured by the SOLSPEC Spectrometer Onboard the International Space Station
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A solar spectrum extending from the extreme ultraviolet to the near-infrared is an important input for solar physics, climate research, and atmospheric physics. Ultraviolet measurements have been conducted since the beginning of the space age, but measurements throughout the contiguous visible and infrared (IR) regions are much more sparse. Ageing is a key problem throughout the entire spectral domain, but most of the effort extended to understand degradation was concentrated on the ultraviolet spectral region, and these mechanisms may not be appropriate in the IR. This problem is further complicated by the scarcity of long-term data sets. Onboard the International Space Station, the SOLSPEC spectrometer measured an IR solar spectral irradiance lower than the one given by ATLAS 3, e.g. by about 7 % at 1 700 nm. We here evaluate the consequences of the lower solar spectral irradiance measurements and present a re-analysis of the on-orbit calibration lamp and solar data trend, which lead to a revised spectrum.
KeywordsGround-based measurements International Space Station Solar infrared spectrum SOLSPEC
The SOLSPEC investigation is supported by the Centre National d’Etudes Spatiales (France), the Centre National de la Recherche Scientifique (France), the Federal Office for Scientific, Technical and Cultural Affairs (Belgium), and the Bundesministerium für Forschung und Technologie (Germany). The participating institutes are the Service d’Aéronomie du CNRS, now LATMOS, the Institut d’Aéronomie Spatiale de Belgique, and the Landessternwarte of Heidelberg. The SOLSPEC absolute calibration has been carried out with the blackbody BB3200g from the Physikalisch-Technische Bundesanstalt (PTB, Braunschweig, Germany). SOLSPEC constitutes an equipment of the external SOLAR payload of the ESA Columbus Laboratory placed onboard the International Space Station. The SOLAR operations are conducted by the Belgium User Support Operations Center (B-USOC) via the COLUMBUS Control Center of DLR (Oberpfaffenhofen, Germany). We thank the World Radiation Monitoring Center-Baseline Surface Radiative Network (WRMC-BSRN) for providing access to the local atmospheric data at the Izaña station. J. Harder, T. Woods, and M. Snow are supported by NASA contract NAS5-97045. The authors thank Vanessa George (LASP) for her support in document preparation.
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