Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center (PMOD/WRC) And is signatory of the Mutual Recognition Arrangement by the Committee of Weights and Measures (CIPM MRA). The PMOD/WRC is the World Radiation Center of the World Meteorological Organisation,

PMOD/WRC Absolute radiometry (ARS) Infrared radiometry (IRS) Optical depth WORCC UV radiometry (WCC-UV) World Radiation Center

EMRP-ENV03 “Solar UV” o Enhance the reliability of spectral solar UV radiation measured at the Earth surface o Develop new techniques and devices for traceability better than 2% (now 5%) and for cost-effective array-spectroradiometer in UV monitoring networks o Intercomparison Campaigns and Workshops Primary Irradiance Standard Transfer StandardReference Spectroradiometer End-User Devices Calibrated UV Network o Project Coordination: Julian Gröbner, Davos o Duration: o Total Budget: 3.9 M€ o 8 Partners EU-NMI; 2 Industry; 2 Universities; > 3 Collaborators (Stakeholders)

Cryogenic radiometer 0.01% Spectral irradiance standard ~1-3% cw-Laser Sources Si-trap detector + aperture Filter Radiometer Blackbody + aperture ~0.3% Detector Source Spectroradiometer Spectrally tuneable source Spectroradiometer ~5% Traceability chain for spectral irradiance Wm -2 nm -1 Portable transfer standard (used for stability check) ~4% Gröbner & Sperfeld, Metrologia, 2006

Validation of the QASUME irradiance reference at PTB Blackbody BB3200pg at PTB Gröbner J., and P. Sperfeld, Direct traceability of the portable QASUME irradiance scale to the primary irradiance standard of the PTB, Metrologia, 42, 134—139, QASUME Validation at PTB in 2004 and 2013 ±1.2%

Quality site audit with the QASUME reference spectroradiometer UV Quality Assurance Program Status site visits 34 sites >150 spectroradiometer intercomparisons Ny Ålesund, Spitzbergen, 2009 RBCC-E, QASUME Gröbner et al., Appl. Opt Gröbner et al., Metrologia, 2006

El Arenosillo “The sunny place” 1999, 2005, 2007, 2009, 2011,

Daily ratios to QASUME: The ideal case

Brewer cosine error

Single Brewer Stray light

Brewer Temperature dependency 6% Temp. coefficient -0.3 %/K

Summary from 6 th RBCC-E (2011)

Wavelength scale

What needs to be addressed?  Temperature dependency  Absolute calibration  Wavelength dispersion  Single Brewer Stray Light  Angular Response  Apply Correction, or better:  Entrance optic modification

Presentations, Guidelines, Publications can be found at the project web-site: Spectral solar UV Intercomparison at Davos & Final ENV03 Workshop, 7-16 July 2014 International Pyrheliometer Comparison (IPC) 2010

Quality site audit with the QASUME reference spectroradiometer UV Quality Assurance Program Status site visits 34 sites >150 spectroradiometer intercomparisons -1 ±14 % Relative Diff. UVB (95% coverage)

QASUME irradiance reference stability: 2004 to 2012

QASUME irradiance reference Based on 7 transfer standards directly calibrated against the primary irradiance normal of the Physikalisch-Technische Bundesanstalt (PTB), in Germany. Primary standard PTB Transfer standard 1000 W FEL lamp Transfer standard 1000 W FEL lamp Transfer standard 1000 W FEL lamp … PTB EUVC/QASUME 250 W portable lamp … Portable QASUME irradiance reference

Spectral UV irradiance site audit procedure PMOD/WRC Spectroradiometer Brewer#163 Portable QASUME reference spectroradiometer Regular intercomparisons Measuring Station Quality Assurance Local Spectroradiometer QASUME Audit report and calibration certificate sent to local operator and published on QASUME irradiance reference traceable to PTB Test report

Comparison of spectroradiometers matSHIC QASUME TEST Ratio TEST/QASUME Same wavelength scale Uniform slit width (1 nm default)

Wavelength scale