Fourth World Radiometric Reference to SI radiometric scale comparison and implications for on-orbit measurements of the total solar irradiance

Abstract

We report the fourth World Radiometric Reference (WRR)-to-SI comparison. At the National Physical Laboratory we compared three transfer pyrheliometer instruments in power mode with the SI radiometric scale. Compared with the three previous comparisons, we improved the experiment by operating the transfer instruments in vacuum. At the Total solar irradiance Radiometer Facility (TRF) located at the Laboratory for Atmospheric and Space Physics (LASP) in Boulder, we repeated the power comparison of one of the transfer instruments. The TRF also allowed the comparison and characterization of this instrument in irradiance mode. Using the WRR comparisons performed in Davos, we find that the WRR is 0.34% higher than the SI scale. Comparing irradiance mode calibrations with power mode calibrations reveals that previous estimates of stray light of PMO6-type radiometers were very low. The instrument calibrated at TRF was integrated in the space experiment PREMOS on the French satellite PICARD and carries the first vacuum irradiance calibration to space.

Assessing the beginning to end-of-mission sensitivity change of the PREcision MOnitor Sensor total solar irradiance radiometer (PREMOS/PICARD)

“…For example, the primary radiometer of SORCE/TIM experienced~200 ppm degradation over the first 10 years of operation (2003-2012Kopp 2014). PMO6 radiometers, which comprise both PREMOS radiometers and one half of the SOHO/VIRGO experiment (see below), can exceed thousands of ppm per decade (Fröhlich 2003;Schmutz et al 2013).…”

“…PMO6 radiometers, which comprise both PREMOS radiometers and one half of the SOHO/VIRGO experiment (see below), can exceed thousands of ppm per decade (Fröhlich 2003;Schmutz et al 2013). For example, the A-sensor of the PREMOS TSI radiometer on the PICARD satellite, ''PREMOS-A'', degraded by almost 3,000 ppm in 2 years of operation, during which it was exposed for 300 days (Fehlmann et al 2012;Schmutz et al 2013). This is why all TSI radiometers in space, other than the Hickey-Frieden (HF; Hickey et al 1988) and Earth Radiation Budget Satellite (ERBE; Lee et al 1995) experiments, had a backup channel in order to account for the degradation in the operating instrument (SORCE/TIM has three; Kopp & Lawrence 2005).…”

Revising shortwave and longwave radiation archives in view of possible revisions of the WSG and WISG reference scales: methods and implications

“…Longwave radiation is broadly defined as covering the ∼ 4-100 µm range (Petty, 2006), while the WISG pyrgeometers cover the range ∼ 4-50 µm (Eppley Precision Infrared Radiometer (PIR) pyrgeometers) and ∼ 4.5-42 µm (Kipp & Zonen CG(R)4 pyrgeometers). Recent measurements with newly developed high-precision ground-based radiometers have demonstrated that a revision of approximately −0.3 % and up to +5 W m −2 of the WSG and WISG scales, respectively, may be required (Fehlmann et al, 2012;Gröbner et al, 2014). Since a large number of shortwave and longwave radiation time series (e.g.…”

“…A large number of radiometers are traceable to the World Standard Group (WSG) for shortwave radiation and the interim World Infrared Standard Group (WISG) for longwave radiation, hosted by the PhysikalischMeteorologisches Observatorium Davos/World Radiation Centre (PMOD/WRC, Davos, Switzerland). The WSG and WISG have recently been found to over-and underestimate radiation values, respectively (Fehlmann et al, 2012; Gröb-ner et al, 2014), although research is still ongoing. In view of a possible revision of the reference scales of both standard groups, this study discusses the methods involved and the implications on existing archives of radiation time series, such as the Baseline Surface Radiation Network (BSRN).…”

Solar Irradiance Variability is Caused by the Magnetic Activity on the Solar Surface

“…variability that is of interest rather than the absolute radiative flux, we normalized the reconstruction and the VIRGO record to the TIM record, the absolute radiometry of which is widely accepted as the most accurate [40][41][42].…”