SOLAR/SOLSPEC mission on ISS: In-flight performance for SSI measurements in the UV

Abstract

Context. The SOLar SPECtrum (SOLSPEC) experiment is part of the Solar Monitoring Observatory (SOLAR) payload, and has been externally mounted on the Columbus module of the International Space Station (ISS) since 2008. SOLAR/SOLSPEC combines three absolutely calibrated double monochromators with concave gratings for measuring the solar spectral irradiance (SSI) from 166 nm to 3088 nm. This physical quantity is a key input for studies of climatology, planetary atmospheres, and solar physics. Aims. A general description of the instrument is given, including in-flight operations and performance of the ultraviolet (UV) channel from 175 nm to 340 nm. Methods. We developed a range of processing and correction methods, which are described in detail. For example, methods for correcting thermal behavior effects, instrument linearity, and especially the accuracy of the wavelength and absolute radiometric scales have been validated by modeling the standard uncertainties. Results. The deliverable is a quiet Sun UV reference solar spectrum as measured by SOLAR/SOLSPEC during the minimum of solar activity prior to cycle 24. Comparisons with other instruments measuring SSI are also presented.

SOLAR-ISS: A new reference spectrum based on SOLAR/SOLSPEC observations

“…Diffusors are placed in front of the entrance slit to ensure full illumination of the first grating and also to reduce the effect of pointing uncertainties during observations. The SOLAR/SOLSPEC instrument also contains seven lamps for checking the responsivity and spectral characteristics of the three channels (Bolsée 2012), thus allowing periodical verification to be made on ground and in orbit. The deuterium lamp (nominal or spare) allows a relative calibration of the UV channel.…”

“…-A solar spectrum from 356 to 400 nm obtained with the VIS channel (Meftah et al 2016a) and another one from 400 to 656 nm obtained also with the VIS channel (Bolsée 2012). -A solar spectrum from 656 to 3000 nm obtained with the IR channel (Meftah et al 2017).…”

“…The aim of this article is to present a new reference solar spectrum (SOLAR-ISS) from 165 to 3000 nm (Meftah et al 2016b) based on recent observations of the SOLAR/SOLSPEC spectrometer on board the International Space Station (Thuillier et al 2009;Bolsée 2012). The SOLAR/SOLSPEC instrument has a rather low spectral resolution and cannot sufficiently resolve many Fraunhofer lines.…”

The high-resolution extraterrestrial solar spectrum (QASUMEFTS) determined from ground-based solar irradiance measurements

“…From top to bottom, Fig. 6 shows the comparison to the solar ET spectra measured with SOLSPEC onboard the International Space Station (the version SOLSPEC_A by Bolsée et al, 2017, andSOLAR_ISS by Meftah et al, 2016), SIM v17 onboard SORCE (Harder et al, 2010), SCIAMACHY (Hilbig et al, 2017), the ATLAS-3 solar spectrum (Thuillier et al, 2003), the Chance-Kurucz solar spectrum (SAO, Smithsonian Astrophysical Observatory; Chance and Kurucz, 2010), a composite solar spectrum made up from a variety of spectra (Gueymard, 2003) and finally another composite solar spectrum corrected by a comparison to ground-based measurements (Egli et al, 2012). The wavelength scales of the five space-based solar spectra were adjusted to air wavelengths to provide a consistent wavelength scale for this comparison.…”

“…For SIM and SOLSPEC_A, the highresolution QASUMEFTS spectrum was convolved with the 1.1 (a) SOLSPEC_A Figure 6. From (a) to (h): ratios between QASUMEFTS and the solar ET spectrum from SOLSPEC (SOLSPEC_A by Bolsée et al, 2017, andSOLAR_ISS by Meftah et al, 2016), SORCE SIM (Harder et al, 2010), SCIAMACHY (Hilbig et al, 2017), ATLAS-3 (Thuillier et al, 2003), SAO (Chance and Kurucz, 2010), the composite from Gueymard (2003) and the composite from Egli et al (2012). The black lines are the ratios convolved with a 1 nm wide triangular slit function, while the red line is a 10 nm running average.…”