Accurate Determination of the TOA Solar Spectral NIR Irradiance Using a Primary Standard Source and the Bouguer–Langley Technique |
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Authors: | D Bolsée N Pereira W Decuyper D Gillotay H Yu P Sperfeld S Pape E Cuevas A Redondas Y Hernandéz M Weber |
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Institution: | 1. BIRA-IASB, 3 Avenue Circulaire, 1180, Brussels, Belgium 2. Physikalisch-Technische Bundesanstalt, Braunschweig, Germany 3. Iza?a Atmospheric Research Center (AEMET), Tenerife, Spain 4. Institut für Umweltphysik, Universit?t Bremen, Bremen, Germany
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Abstract: | We describe an instrument dedicated to measuring the top of atmosphere (TOA) solar spectral irradiance (SSI) in the near-infrared (NIR) between 600 nm and 2300 nm at a resolution of 10 nm. Ground-based measurements are performed through atmospheric NIR windows and the TOA SSI values are extrapolated using the Bouguer–Langley technique. The interest in this spectral range arises because it plays a main role in the Earth’s radiative budget and also because it is employed to validate models used in solar physics. Moreover, some differences were observed between recent ground-based and space-based instruments that take measurements in the NIR and the reference SOLSPEC(ATLAS3) spectrum. In the 1.6 μm region, the deviations vary from 6 % to 10 %. Our measuring system named IRSPERAD has been designed by Bentham (UK) and has been radiometrically characterized and absolutely calibrated against a blackbody at the Belgian Institute for Space Aeronomy and at the Physikalisch-Technische Bundesanstalt (Germany), respectively. A four-month measurement campaign was carried out at the Izaña Atmospheric Observatory (Canary Islands, 2367 m a.s.l.). A set of top-quality solar measurements was processed to obtain the TOA SSI in the NIR windows. We obtained an average standard uncertainty of 1 % for 0.8 μm<λ<2.3 μm. At 1.6 μm, corresponding to the minimum opacity of the solar photosphere, we obtained an irradiance of 234.31±1.29 mWm?2?nm?1. Between 1.6 μm and 2.3 μm, our measurements show a disagreement varying from 6 % to 8 % relative to ATLAS3, which is not explained by the declared standard uncertainties of the two experiments. |
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