TRACEABLE SOLAR RADIATION MEASUREMENTS

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1 TRACEABLE SOLAR RADIATION MEASUREMENTS Julian Gröbner, Natalia Kouremeti, Gregor Hülsen, Stelios Kazadzis, Luca Egli Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center (PMOD/WRC)

2 Outline The World Radiation Center at PMOD/WRC Metrology Research in Europe The radiometric laboratory at PMOD/WRC ATLAS A tuneable laser for the characterisation of spectrometers

3 The 4 Pillars of PMOD/WRC World Radiation Center WSG Satellite experiments Instrument development PSR TSI = Total Solar Irradiance PMOD TSI-composite Scientific Research: Investigating The influence of the Sun on Climate Radiation Balance Interaction Atmosphere - Radiation

4 The 2 Worlds of PMOD/WRC The PMOD/WRC is designated World Radiation Center by the WMO: operates instruments representing radiation quantities accepted as world reference standards by the WMO Calibrates meteorological radiation instruments Provides traceable measurements to SI PMOD/WRC represents WMO in the CIPM MRA for solar irradiance The PMOD/WRC is designated Institute of METAS for solar irradiance: Signatory of the CIPM MRA Implementation of a Quality System according to ISO Holder of 6 CMC's for solar irradiance

5 PMOD/WRC as World Radiation Center BIPM CCPR MRA WMO (World Meteorological Organization) Commission for Instruments and Methods of Observations (CIMO) World Radiation Center (WRC) Infrared Radiometry Section (WRC-IRS) since 2004 since 1996 since 1971 since 2013 World Optical Depth Research and Calibration Center (WORCC) Solar Radiometry Section (WRC-SRS) 2 CMC's World Calibration Center for UV (WCC-UV) 4 CMC's

6 Solar UV Quality Assurance Program On site comparison with the portable QASUME reference spectroradiometer Status site visits 36 sites Over 150 spectroradiometer intercomparisons Ny-Ålesund, 2009 Lauder, 2016 Test QASUME = 1±14% 6

7 4 th Filter Radiometer Comparison (FRC-IV) 28 September 16 October Instruments 12 Countries 3 Global 4 National Networks Aerosol Optical Depth at 500 nm CIMELs SPO PFRs POM-2 MFRSR PSR

8 The European Metrology Research Programme (EMRP) & The European Metrology Programme for Innovation and Research (EMPIR)

9 A decade of Metrology projects for Environment in the field of Radiometry METEOC I METEOC II METEOC III Metrology for earth observation and climate 3 (Proposed) SolarUV ATMOZ MetAQ Metrology for UV/Vis remote sensing of air quality (Proposed)

10 Traceability chain for spectral irradiance at PTB Detector-based cw-laser sources Cryogenic radiometer Si-trap detector + aperture Source-based Detector Source Spectrally tuneable source Filter Radiometer Blackbody + aperture Tunable lasers (Aim of EMRP SolarUV) Transfer standards Spectroradiometer U=±0.3% U=±1.1%

11 Traceability chain for spectral irradiance at PTB Detector-based cw-laser sources Cryogenic radiometer Si-trap detector + aperture Source-based Detector Source Spectrally tuneable source Filter Radiometer INTENSITY Blackbody + aperture Tunable lasers (Aim of EMRP SolarUV) x100 Transfer standards Spectroradiometer U=±0.3% U=±1.1%

12 Traceability to SI-units QASUME / PTB Hülsen et al., Traceability of solar UV measurements using the QASUME reference spectroradiometer, Applied Optics, 55, , TULIP F300 F301 F304 F324 F330 F364 F376 BB 2013 BB Wavelength /nm U ±1.1%

13 EMRP ATMOZ: A traceable and harmonized Global Total Column Ozone Network Radiometry Atmospheric model Measurement Total column Ozone retrieval model O 3 Value + = Uncertainty of measurement: Uncertainty of model: Uncertainty of O 3 Wavelength uncertainty Bandpass (FWHM) Uncertainty of calibration Sensitivity of the detector: NEI: Noise equivalent irr. selected wavelength range selected cross-section selected atmospheric temperature computational uncertainty extraterrestrial spectrum air mass range value

14 EMRP ATMOZ: A traceable and harmonized Global Total Column Ozone Network Radiometric Characterization of Three Reference Dobson Spectrophotometers Ozone measurements at Izaña ORIGINAL SLITS MEASURED Preliminary data, Courtesy U. Köhler

15 Radiometry with Tuneable Lasers ATLAS, PMOD/WRC Tuneable lasers have revolutionized the field of radiometry SIRCUS facility, NIST, from Y. Zong, NEWRAD 2005

16 Tuneable laser applications in Radiometry Line-spread function Characterisations Stray Light correction of array spectroradiometers Linearity Spectral irradiance/radiance responsivity calibrations

17 Tuneable laser setup at PMOD/WRC Microlens array Filterwheel Wedge filter OPO Laser Radiometer Wavemeter Monitor Detector 0.3 NT242 Laser 1 ATLAS Tuneable Laser output Tuning range nm Pulse 5 ns repetition rate 1000 Hz Pulse power at 450 nm ~300 mw A.U WL= nm FWHM = 5.7 pm Wavelength /nm A.U Wavelength /nm

18 ATLAS Tuneable laser facility Tuneable laser Entrance optic Microlens array Filterwheel Wavemeter Monitor detector

19 Instrument characterisations performed on the ATLAS setup Phaethon/Avantes DOAS/ mini MAXDOAS System PSR 006/ PMOD/WRC- spectral aerosol optical depth PFR N02 / GAWPFR 4 channel Lunar photometer ERMIS - DOAS/MAXDOAS system Pandora #120 /PANDONIA (deployed at PMOD/WRC since April 2016)

20 Line-Spread function measurement 10 0 To achieve sufficient dynamic range measurements at different saturation levels are combined into one line spread function PSR nm 10-1 Normlised orders of magnitude Pixel

21 Line-Spread Functions

22 10 0 Line-spread functions and stray-light in Array Spectroradiometers 10-2 Internal reflections and second order effects produce spectrally varying slit functions Pixel 10 6 Oor Radiation 10 4 Laser WL>640 nm Out-of-range stray-light even though low-pass filters should cut longer wavelength radiation (filter leakage) 1000ms Wavelength /nm

23 In-band Stray-light correction The stray-light corrected in-band signal Y IB can be retrieved from the measurement by applying a stray-light correction matrix A -1 to the measured signal, following the method of Zong, Y IB =A -1 Y meas Slit Function wavelength(nm)

24 In-band Stray light correction procedure for array spectroradiometers Gaussian fit 10 0 from Zong et al, 2006 Slit Functions obtained from tuneable laser setup 10 Straylight from uniform spectrum Normalised 10-4 Stray Light /% Pixel Pixel

25 100 Stray-light correction 1.25 Irradiance /mwm -2 nm FEL Lamp Wavelength /nm SR-Correction In-Range Stray light Correction Wavelength /nm Irradiance /mwm -2 nm Sun In-Range Stray light Correction Uncertainty in the correction is small <10% Wavelength /nm Wavelength /nm

26 Counts Validation of stray-light correction Using solar measurements and cut-off filters Sun Filter Y510 on RAW DARK SR_Corrected Counts Counts Wavelength /nm Y420 filter RAW DARK SR_Corrected Wavelength /nm Wavelength /nm Filter Transmission 10 0 Y420nm filter FILTER SR_CORR RAW Wavelength /nm The Stray-Light can be reduced by ~ factor 10

27 The Radiometric laboratory at PMOD/WRC Global Spectral irradiance calibration Spectral responsivity Direct Spectral irradiance calibration ATLAS Tuneable Laser QA4EO-ATLAS is funded through IDEAS+ SPPA

28 Characterization of Moonphotometer (Lunar PFR) Linearity Determination of PFR internal gain Spectral filter responsivity Direct Irradiance Calibration Setup Response (V/W.m -2 )

29 Spectral characterization of Moonphotometer Spectral responsivity, Spectral region nm Filter Central Wavelength (nm) Filter Function Out-of-band rejection Filter Central Wavelength (nm) wavelength offset (nm) 10-2 Filter Function wavelength offset (nm)

30 Characterization of Moonphotometer Direct Irradiance calibration Responsivity V W -1 m 2 Irradiance at reference distance Determination of optical reference plane using point source and square law Irradiance - Lamp F467 (W.nm-1.m -2 ) F Dark Corrected Signal -1/2 (mv -1/2 ) wavelength (nm) Distance from Lamp (mm)

31 Field Characterisation devices developed in EMRP SolarUV and ATMOZ UV-LED field calibration device Birefringence-based UV wavelength ruler Tuneable portable source (TuPS) A multichip LED device (9 LEDs in a single TO8 package) The UV-LED device mounted in a temperature controlled housing, Drift < 0.05 %/h Upgraded ruler from SolarUV Lines every ~4 nm Improved characterization, Directly traceable to the meter Tuneable range nm Uncertainty ±0.05 nm UV Cathode or Laser Driven Light Source

32 Conclusion/Outlook There is currently a paradigm shift in the metrology community : From providing traceability of radiometric measurements to providing traceability of atmospheric remote sensing products : EMRP SolarUV Traceability of solar UV irradiance measurements : EMRP ATMOZ Traceability for atmospheric total column ozone : EMPIR metaq Metrology for UV/Vis remote sensing of air quality NEWRAD th International conference New Developments and Applications in Optical Radiometry June 2017 Tokyo, Japan (Pending approval)