Abstract
Abstract. A high-resolution extraterrestrial solar spectrum has been determined from ground-based measurements of direct solar spectral irradiance (SSI) over the wavelength range from 300 to 500 nm using the Langley-plot technique. The measurements were obtained at the Izaña Atmospheric Research Centre from the Agencia Estatal de Meteorología, Tenerife, Spain, during the period 12 to 24 September 2016. This solar spectrum (QASUMEFTS) was combined from medium-resolution (bandpass of 0.86 nm) measurements of the QASUME (Quality Assurance of Spectral Ultraviolet Measurements in Europe) spectroradiometer in the wavelength range from 300 to 500 nm and high-resolution measurements (0.025 nm) from a Fourier transform spectroradiometer (FTS) over the wavelength range from 305 to 380 nm. The Kitt Peak solar flux atlas was used to extend this high-resolution solar spectrum to 500 nm. The expanded uncertainties of this solar spectrum are 2 % between 310 and 500 nm and 4 % at 300 nm. The comparison of this solar spectrum with solar spectra measured in space (top of the atmosphere) gave very good agreements in some cases, while in some other cases discrepancies of up to 5 % were observed. The QASUMEFTS solar spectrum represents a benchmark dataset with uncertainties lower than anything previously published. The metrological traceability of the measurements to the International System of Units (SI) is assured by an unbroken chain of calibrations leading to the primary spectral irradiance standard of the Physikalisch-Technische Bundesanstalt in Germany.
Highlights
Quantifying the spectral solar radiation penetrating the atmosphere is crucial to understand and quantify its interaction with the atmosphere, oceans and the surface
The QASUMEFTS solar spectrum represents a benchmark dataset with uncertainties lower than anything previously published
In this study we present ground-based direct spectral solar irradiance measurements obtained with the transportable reference double monochromator spectroradiometer QASUME (Quality Assurance of Spectral Ultraviolet Measurements in Europe) and a high-resolution Fourier transform spectroradiometer (FTS) over the wavelength range from 300 to 500 nm and from 300 to 390 nm respectively
Summary
Quantifying the spectral solar radiation penetrating the atmosphere is crucial to understand and quantify its interaction with the atmosphere, oceans and the surface. Bais, 1997; Gröbner and Kerr, 2001; Bolsée et al, 2014) or sun photometers (Schmid and Wehrli, 1995) were used to determine the spectral solar spectrum in wavelength regions unaffected by strong atmospheric absorption features. These measurements were either used for atmospheric research or for the validation of existing solar extraterrestrial spectra obtained from space measurements or from models of the sun (Fontenla et al, 2006; Shapiro et al, 2010). A highresolution absolute extraterrestrial solar spectrum is derived by applying the Langley-plot technique to the measurements of each instrument before combining them to a single high-resolution solar extraterrestrial spectrum
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