SOLAR/SOLSPEC: Scientific Objectives, Instrument Performance and Its Absolute Calibration Using a Blackbody as Primary Standard Source

Abstract

SOLAR is a set of three solar instruments measuring the total and spectral absolute irradiance from 16 nm to 3080 nm for solar, atmospheric and climatology physics. It is an external payload for the COLUMBUS laboratory launched on 7 February 2008. The mission's primary objective is the measurement of the solar irradiance with the highest possible accuracy, and its variability using the following instruments: SOL-ACES (SOLar Auto-Calibrating EUV/UV Spectrophotometers) consists of four grazing incidence planar gratings measuring from 16 nm to 220 nm; SOLSPEC (SOLar SPECtrum) consists of three double gratings spectrometers, covering the range 165 nm to 3080 nm; and SOVIM (SOlar Variability Irradiance Monitor) is combining two types of absolute radiometers and threechannel filter -radiometers. SOLSPEC and SOL-ACES have been calibrated by primary standard radiation sources of the Physikalisch-Technische Bundesanstalt (PTB). Below we describe SOLSPEC, and its performance.Keywords International space station · SOLAR · SOLSPEC · Sun spectrum · PTB · Solar irradiance Scientific BackgroundThree instruments, SOL-ACES, SOLSPEC and SOVIM, have been selected to simultaneously measure the spectral and total solar irradiance. They are briefly described by G. Thuillier ( ) · T. Foujols ·

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

“…V0132 and BR066) calibrated under vacuum in radiant intensity µW sr −1 nm −1 at PTB (BESSY II facility, Berlin) (Beckhoff et al 2009). The conversion of the lamps' calibration spectra to spectral irradiance and the good consistency between responsivity R(λ) obtained from the blackbody and deuterium lamps has been discussed in Thuillier et al (2009). We will refer to E D 2 and S D 2 respectively for the SI of the deuterium lamps and the accumulated signal measured by SOLAR/SOLSPEC.…”

“…Mechanical shutters and quartz plates were added to shield against short wavelength radiation and contaminants around ISS to limit the degradation of optical components. To accurately monitor and maintain the absolute radiometric and wavelength response during the long-term mission, the internal calibration lamp unit was fully redesigned and improved (Thuillier et al 2009). The general design of the optics was maintained and the whole instrument based on three independent double spectroradiometers, and we were able to improve the optical alignment of the spectrometers relative to ATLAS 3.…”

“…These lamps (named D 1 and D 2 ) have an integrated MgF 2 lens for collimation, replacing the front window. Their collimated beam is collected by a concave mirror Al + MgF 2 which is coated to ensure the diffuser is well illuminated (Thuillier et al 2009;Bolsée 2012). A field lens followed by an actuator is inserted between the exit slit and the detector to condense, homogenize and attenuate (when required) the signal reaching the detector.…”

“…The variable p is the motor step. Owing to small adjustments during instrument assembly, instead of using the purely theoretical values, we adjusted them using a nonlinear regression of this function over a sample of spectral line positions {p i , λ i } obtained experimentally from the spectra of laboratory spectral lamps measured by SOLAR/SOLSPEC (Thuillier et al 2009). The best estimate values are shown in Table 2.…”

“…At this step, we normalize the linearized signal S net to the level that would have been obtained in the PTB temperature environment. It is performed using a tabulated curve of the temperature sensitivity coefficient α T , relevant for the Cs 2 Te photocathode and the photon counting mode as discussed in Thuillier et al (2009) and Bolsée (2012). The solar blind PMT is more sensitive at lower temperatures (α T < 0) for wavelengths shorter than 290 nm.…”