t h The 12 t h International Pyrheliometer Comparison IPC-XII 29. September 2016, TECO-2016, Madrid Wolfgang Finsterle Physikalisch-Meteorologisches Observatorium Davos World Radiation Center
Outline What are IPCs? Why do we need IPCs? Who cares? How does it work? What is special about solar irradiance? Metrology Standardization IPC-XII Participation Results and Conclusions Future of IPCs
What are IPCs?
The purpose of this undertaking was to secure the comparability of all meteorological radiation measurements throughout the world, on the one hand retrospectively for all observations of IGY and IGC (1957/1959) the results of which had to the greater part not yet been published, on the other hand for future observations of radiation. (from IPC-I Report, WMO CIMO-III/Doc. 37, 1962)
1959: The modest target There should be a well standardized pyrheliometer available in many countries on each continent (as far as possible) which could serve as standard for calibrations in the region. ( The important task to undertake a new absolute standardization or to create a new absolute basis for a pyrheliometric standard scale was left completely out of consideration. ) homogenization
The extended target...the urgent need of methods of standardization not based upon a specific instrument but rather upon a well-defined procedure which is standardized, reproducible, and repeatable at all times and places. Fröhlich, Proc. 2 nd Symp. Meteor. Obs. Instrum. AMS, 1972 The World Radiometric Reference WRR was defined based on the average of 15 absolute cavity radiometers, and the World Standard Group WSG was established to realize the WRR. WMO-No. 490, Annex IV, CIMO-VII, 1977 In 2010 WMO joined the CIPM MRA. The WRR became a primary standard within the SI. The stability of the WSG is validated during IPCs. standardization
Build and share knowledge IPC-XII seminar
homogenization standardization to build and share knowledge
Who cares? Regional and National Radiation Centres RRC are required per CIMO Guide to compare their standard pyrheliometers with the WSG during IPCs Meteo agencies To provide traceability to their solar radiation networks Radiometer manufacturers To showcase their products Research institutions Solar energy sector Traceability National Metrology Institutes To provide traceability to their irradiance references IPC stakeholders
How does it work? new WRR 1 st Step: Average of WSG pyrheliometers corrected with old WRR factor = new WRR old WRR Factor old WRR Factor old WRR Factor old WRR Factor old WRR Factor old WRR Factor standardization WSG
new WRR Factor new WRR Factor new WRR Factor new WRR Factor new WRR Factor new WRR Factor Standardization new WRR 2 nd Step: Ratio of new WRR to WSG pyrheliometers = new WRR Factors WSG
Homogenization new WRR WSG 3 rd Step: Ratio of new WRR to participating pyrheliometers = new WRR Factors
Homogenization new WRR WSG 3 rd Step: Ratio of new WRR to participating pyrheliometers = new WRR Factors
Stability check new WRR WSG stability check 4 th Step (stability check): Average ratio of old to new WRR factors should be unity.
IPC procedures 1.Determine new WRR from valid WSG with old WRR factors Apply data selection criteria Calculate average of at least 4 WSG pyrheliometers 2.Determine new WRR factors for all WSG pyrheliometers Calculate ratios of the new WRR to each WSG pyrheliometer Re-assess data selection Iterate 1. and 2. as appropriate 3.Calculate new WRR factors for participating pyrheliometers 4.Estimate stability of WSG from average inter-ipc drift of WRR factors of participating pyrheliometers
Stability of the WSG
What is special about Solar Irradiance? Field pyrheliometers Field pyranometers Reference pyrheliometers Reference pyranometers WRR World Radiometric Reference (WRR) Established by WMO (CIMO Guide) Recognized by BIPM through CIPM MRA CMCs approved (KCDB) Currently no traceability to SI base units traceability island
Proposed future traceability chain for Solar Irradiance Field pyrheliometers Field pyranometers Reference pyrheliometers Reference pyranometers WRR Cryogenic Solar Absolute Radiometer (CSAR) BIPM key comparisons m kg SI- Base Units K mol cd A s traceable to SI base units
0.5±0.4% S c a l e -5.0±0.4% 2.2±0.4% ~0.3%? Technology Evolution of solar radiometry and irradiance scales 1893 Ångström Pyrheliometer 1911 Silverdisk Pyrheliometer (calibrated against self-calibrating water-stir instrument) 1905 Ångström Scale (International Meteorological Conference, Innsbruck) 1913 Smithsonian Scale 1956 Definition of of the International Pyrheliometric Scale IPS-56 1970 Absolute Cavity Pyrheliometer 1971 WRC 1977 Definition of of the World Radiometric Reference WRR 2010 Cryogenic Solar Absolute Radiometer (CSAR) 2??? Cryogenic Scale?
IPC-XII 111 individuals 33 countries 134 pyrheliometers 15 RRC, 15 NRC 26 other institutions and manufacturers world-wide coverage
IPC-XII 578 WRR data points 9 measurement days in 3-weeks period Temperature, humidity, pressure 3 wind stations throughout the measurement field Scattering parameters AOD @ 367.6, 412.0, 501.2, and 862.4 nm Ångström exponents, Ozone data base
IPC-XII Online registration opened 6 months prior to start of the campaign Invitation letters were sent to registered participants for visa purposes Negotiation with local hotels for accommodation deal Arrangement with MeteoSwiss for local weather and cloud forecast during IPC-XII Arrangement with Skyguide (ATC) to reduce contrails over IPC-XII site preparations
Storage space
Working space Storage space
Working space Storage space Connectivity power and data
Time server and reference clock Working space Storage space Connectivity power and data
Time server and reference clock Working space Storage space Connectivity power and data Shipping
IPC-XII
Results New WRR factors for the WSG pyrheliometers computed with PMO2, PMO5, CROM2L, and PAC3 and their respective WRR factors from IPC-XI (2010).
http://pmodwrc.ch/pdf/ ipcxii-report.pdf
Cryogenic Solar Absolute Radiometer CSAR Mechanical cooler quartz window 10 mm receiver cavity 20 K reference block
CSAR & MITRA
CSAR Measurements 2015-06-30 SI to WSG: - 0.22% ± 0.053% (k = 1) IPC-XII measurement day # CIMO Task Team on Radiation References
IPgC-II and FRC-IV In conjunction with the IPC-XII 2 nd International Pyrgeometer Comparison (IPgC-II) 4 th Filterradiometer Comparison (FRC-IV) Stay tuned for the upcoming presentation by Julian Gröbner on the IPgC-II!
Wolfgang Finsterle, wolfgang@pmodwrc.ch Thank you for your attention!
Traceability to SI base units NMI (Switzerland: METAS) SI- Base Units c N A e k B h m kg K mol cd A s Josephson effect 2e/h Quantum Hall effect h/e 2 Aperture Area [m 2 ] Standard Volt Standard Ohm Transfer Multimeter m 2 Pyrheliometer W Markus Suter, 2014
± 400 ppm WRR Standard - Conventional SI/WMO Standard - Solar Irradiance - Artefact based - Ambient Air SI- Base Units ( kg, m, s, ) ± 3000 ppm ± 700 ppm ± 140 ppm Cryogenic Laboratory Standard - SI - Laser Power - Vacuum - est. 2007 Cryogenic Solar Absolute Radiometer (CSAR) (Vac/Ambient) ± 200 ppm ± 380 ppm <± (300ppm) ± 10 ppm Cryogenic Radiometer (Vacuum) Native Scale WRR Scale SI-Lab Scale CSAR Scale Measurement (Solar Irradiance) [W/m 2 ] Radiant Power [W] uncertainties are indicated for k=2