Spectroradiometer characterisations for traceable solar radiation measurements

Transcription

1 Spectroradiometer characterisations for traceable solar radiation measurements Julian Gröbner, Natalia Kouremeti, Stelios Kazadzis, Gregor Hülsen, Luca Egli Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center, PMOD/WRC

2 Outline Measurement traceability, Spectral solar irradiance measurements Total column ozone Aerosol optical depth

3 Traceable solar radiation measurements 2.41 metrological traceability property of a measurement result whereby the result can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty What it actually means: (1) An unbroken chain of comparisons going back to stated references acceptable to the parties, usually a national or international standard; (2) Documented measurement uncertainty; the uncertainty of measurement for each step in the traceability chain must be calculated or estimated according to agreed methods and must be stated so that an overall uncertainty for the whole chain may be calculated or estimated; (3) Documented procedures; each step in the chain must be performed according to documented and generally acknowledged procedures; the results must be recorded; (4) Technical competence; the laboratories or bodies performing one or more steps in the chain must supply evidence for their technical competence (e.g. participation in interlaboratory comparisons); (5) Reference to SI units; the chain of comparisons must, where possible, end at primary standards for the realisation of the SI units; (6) Calibration intervals; calibrations must be repeated at appropriate and established intervals; (7) Measurement assurance; a proper measurement assurance program must be established to ensure the validity of the measurement process and the accuracy of standards used at the time of the measurement. from Traceability of measurement, ILAC-G2: 1994

4 Solar UV ( ) and ATMOZ ( ) EMRP SolarUV ( ) 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%) Primary spectral Irradiance Standard Transfer Standard Reference Spectroradiometer End-User Devices Calibrated UV Network EMRP ATMOZ ( ) o Significantly enhance the reliability of total ozone column determined at Earths surface o A traceable and harmonized global total column ozone network within 1%

5 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 Spectroradiometer Transfer standards U=±0.3% U=±1.1%

6 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 x100 Transfer standards Spectroradiometer U=±0.3% U=±1.1%

7 Uncertainty Budget QASUME reference spectroradiometer Uncertainty Parameter Relative Std Uncertainty % QASUME QASUMEII Radiometric calibration W lamp stability (one year) 0.10 Nonlinearity... From PMT or PC ND filter transmission n/a 0.3 Stability Temperature Dependence, Entrance optic (-0.11%/K) 0.2 (Temp-Stability ±3 K result in 0.33/ 3) Angular Response (Clear Sky) 0.6 Angular Response (Overcast) 0.3 (full scale 1%, 0.5/ 3) Repeatability (std noise) (wl>=310nm) 0.2 Repeatability (std noise) (wl=300nm, SZA=75 ) 3.5 Wavelength shift (after matshic) Δwl=0.02 nm 0.1, 0.5 at wl=300 nm Combined Uncertainty 1.0 (overcast, SZA<65 : 0.8) 1.0 (overcast, SZA<65 : 0.8) Expanded Uncertainty (k=2) 1.9 (overcast: 1.6) 2.0 (overcast:1.6) Expanded Uncertainty (k=2) 300 nm, SZA= Hülsen et al., Applied Optics, 2016

8 Validation of the WCC-UV spectral irradiance reference at PTB TULIP tunable laser setup Trap PTB Einsteinbau QASUME PTB Reinraum Tuneable Laser facility TULIP PMOD/WRC Wavelength by wavelength integration ±1% TRAP = mwm 2 nm -1 QASUME = mwm 2 nm -1 Gröbner & Sperfeld, Metrologia, 2005 Hülsen at al., Applied Optics 2016

9 EMRP ATMOZ: Traceable Ozone Measurements Radiometry Atmospheric Model Solar Measurement Total Column Retrieval Method O 3 Value Uncertainty of measurement: + Uncertainty of model: = Uncertainty of O 3 value Measurements & Characterizations: Field campaigns Laboratory visits Benchmark Datasets: New ozone cross-sections New extraterrestrial spectrum Uncertainty Budget: Monte-Carlo-Model approach

10 A traceable extraterrestrial solar spectrum: QASUMEFTS Izaña, September 2016 QASUME U QASUME = 2.0% (k=2) λ 310 nm Wavelength traceability to SI through FTS U<10pm ATLAS-3 Fourier Transform Spec. Gröbner et al., 2017

11 ATMOZ Field campaign Izaña, 2016 Brewer TRIAD ±1% Full spectrum U QASUME =1.3 % U BREWER =1.4 %

12 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

13 Spectroradiometer characterisations performed on the ATLAS setup Phaethon/Avantes DOAS/ mini MAXDOAS System PSR 006/ PSR008 - spectral irradiance / AOD ERMIS - DOAS/MAXDOAS system RAMSES Lidar Spectroradiometer /DWD Pandora #120 /PANDONIA (deployed at PMOD/WRC since April 2016)

14 Precision solar spectroradiometer for Solar irradiance and AOD (PSR) Holographic flat-field grating 200 lines/mm from Zeiss Hamamatsu NMOS 1024 linear image sensor Temperature stabilized sensor ±0.1K (invar) Temperature insensitive optical bench (carbon) 18 bit ADC ( 262 kcounts) Integration Time: 10 ms to 40 sec Wavelength range nm Resolution 1.5 nm to 6 nm Wavelength step 0.7 nm Stray-light optimized optical design with zero-order light-trap Second-order diffraction: Cut-On filter (540nm) with rejection efficiency 99.9% for wavelengths<440nm Entrance optics: Direct Irradiance telescope - F.O.V ~1 deg Generic SMA connector for Custom Input Optics (e.g. Global Irradiance Head)

15 PSR Characterisation Nonlinearity <0.5% Temperature coefficients Sensitivity <0.1%/K dwl ~0.02 nm/k dfwhm<0.005 nm/k Stray-Light ~10-5 Telescope Flat-field ~±0.6% over 1 field of view Direct irradiance calibration ~±3% Slit function and bandpass

16 Direct irradiance calibration Responsivity (counts per ms./ [mw.m -2.nm -1 )]) Dist= mm T S =26.63 Dist= mm T S =26.97 Dist= mm T S = wavelength (nm) Primary Irradiance Standard Lamp: type FEL 1000 W Inverse Square Law Ratio to Final Response Function Response (counts per ms./ [mw.m -2.nm -1 )]) wavelength (nm) 50 Dist= mm PSR_006 Calibration 06-Oct-2015 T S =20.30,T B meas=26.63 Combined with Dist= mm T S =20.30,T B meas=26.97 Smoothed wavelength (nm) U PSR 3.0 %

17 100 Stray-light correction Irradiance /mwm -2 nm-1 Irradiance /mwm -2 nm FEL Lamp Wavelength /nm Sun SR-Correction Uncertainty in the correction is about 10% Stray Light Contribution (%) wavelength (nm) O 2 absorption band PSR_006 PSR_ Wavelength /nm

18 PSR AOD from Langley based calibration Izaña, Tenerife, Spain (28.3 N, 16.5 W, 2372m) March - April nm 800 nm Langley based and literature solar ET Spectrum 350 nm 870 nm 500 nm U WMO =0.005±0.01/m Barreto, et. al, 2016.

19 Spectral AOD from Langley and Absolutely calibrated spectroradiometers Expanded uncertainties: U CIMEL/PFR U QASUME U PSR =0.005±0.01/m =0.005±0.02/m =0.005±0.03/m

20 Spectral AOD from absolutely calibrated spectroradiometers nm Advantages of using absolutely calibrated spectra and literature extraterrestrial spectrum: No need for Langley calibrations Recalibrations can be done frequently and when necessary Optical depth retrieval also possible in saturated regions (e.g. water vapour) A step towards metrological traceability of AOD

21 Outlook ATLAS Phase 3 ( /6) Operate 3 precision solar spectroradiometers (PSR) Direct solar irradiance measurements 300 nm nm Determine uncertainty budget for direct solar irradiance & spectral AOD Validate measurements with respect to PFR Triad and QASUME Evaluate Total column ozone and AOD product from Pandora #120 with respect to Brewer/Dobson/QASUME and PSR&PFR Objective: Demonstrate traceability of TOC and AOD measurements