1. Results of Baltic Region Pyrheliometer Comparison, BRPC-2012
Thomas Carlund
Swedish Meteorological & Hydrological Institute (SMHI)
(Currently at PMOD/WRC)
IPC-XII Symposium, PMOD/WRC, Davos, Switzerland.

2. Pyrheliometer comparison Pyranometer comparison
RRC
Norrköping

3. BRPC-2012 Pyrheliometer comparison
Participants
11 cavity pyrheliometers
7 institutions
5 countries

4. Measurements Measurement cadence/series as during IPC’s
Reference: Mean of 8 of the participating instruments which all had WRR-factors from IPC-XI
Data selection criteria:

5. Measurement conditions
AOD nm for IPCs

6. Some example plots FMI, Finland VNIIOFI, Russia SP, Sweden
LHMS, Lithuania
MGO, Russia
PMOD/WRC

7. BRPC-2012 Pyrheliometer comparison
Summary of results
Measurements made on 6 days
Data from 4 days used in the final evaluation
>300 valid data points for most participating instruments
All instruments deviated on average less than 1‰ from the reference
The standard deviation was less than 1‰ for all instruments except one
The average of the ratios of the three PMOD/WRC instruments to the BRPC reference was
Conclusion: BRPC-2012 was a successful pyrheliometer comparison

8. BRPC-2012 Pyrheliometer comparison
Final results

9. Pyranometer comparison
BRPC-2012
Pyranometer comparison
During BRPC-2012 also a small pyranometer comparison was carried out
10 pyranometers from 7 countries
Calibration and ventilation from their home institutions
Pyranometer models: CM10, CM11, CMP11, CM21, CMP21, CM22, LP02, Star
References: CH1#030347CaF2 and CM21# calibrated against the BRPC reference.

10. BRPC-2012 Pyranometer comparison
Participants

11. BRPC-2012 Pyranometer comparison
Field references
CH1s
Shaded, ventilated and netIR offset corrected CM21s.
(Two 2AP GD tracker in «clock mode»)
Calibrated against the BRPC-2012 reference

12. BRPC-2012 Pyranometer comparison
Measurement conditions

13. All except one pyranometer within ±1% from reference!
BRPC-2012 Pyranometer comparison
Main result
Relative deviation from reference for 6-days accumulated global irradiation
Reference (Pyrheliometer+shaded pyranometer)
All except one pyranometer within ±1% from reference!

14. BRPC-2012 Pyranometer comparison
Results
Comparison of 1-minute mean values
Examples for instruments which deviated less than 0.6% from the reference for accumulated values:

15. Comparison of 1-minute mean values
Very good
agreement

16. Comparison of 1-minute mean values
Good
agreement

17. Comparison of 1-minute mean values
Good
agreement

18. Comparison of 1-minute mean values
Slightly less
agreement

19. Comparison of 1-minute mean values
Less
agreement

20. Comparison of 1-minute mean values
Even less
agreement

21. Comparison of 1-minute mean values
The least
agreement
This one deviated 1.4 % from the reference 6-day global irradiation

22. Results for accumulated irradiation after calibration of all instruments using SMHI routine (component sum) calibration
Relative deviation from reference for 6-days accumulated global irradiation
2-3 times lower std dev than with responsivities from users
Instruments 5-13: Mean= 0.27 %, Std.dev.= 0.23 %
Maybe there is a potential for us at the Met services who are responsible for the the pyranometer calibrations to perform/derive more homogenous results?

23. Pyranometer daytime thermal offset
Result of capping experiment under clear sky
Only ventilated instruments above -3 Wm-2

24. Pyranometer nighttime and daytime thermal offset
Linear offset functions determined from nighttime data (black lines) and from capping (blue or green lines), respectively, versus (shaded) thermopile signal (netIR) from a shaded pyrgeometer.

25. Conclusion
Using the netIR offset correction determined by capping sometimes improves the measurements at solar elevations >15° to 20 °, but not always.

26. Results for accumulated irradiation after calibration of all instruments using netIR thermal offset correctionand SMHI routine (component sum) calibration
Relative deviation from reference for 6-days accumulated global irradiation
Instruments 5-13: Mean= 0.64 %, Std.dev.= 0.25 %

27. Conclusions
With one exception the accumulated results of the participating global pyranometers were within ±1 % from the reference global irradiation over 6 days during BRPC-2012.
Based on the BRPC-2012 pyranometer comparison results, it is anticipated that pyranometer measurements from several European countries between 45°-60°N agree fairly well for annual irradiation values and for monthly irradiation values from the summer half year. The precision should be within 2 %. Total uncertainties are higher.
Global radiation measurements using pyrheliometer and shaded pyranometer show the best agreement with the reference
For global radiation measurements ventilated pyranometers of the same type as the shaded reference pyranometers show the best agreement with the reference
Instruments should be compared to the same or a better type of instrument.
The thermal offset is still an uncertain source of uncertainty
It would be interesting to perform a longer pyranometer comparison which also includes more different instrument models. Any volunteers?

28. Thanks for your attention!
More detailed info can be found on the web at , look for IOM 112.
Or the direct link:

29. Ratio of Responsivity from BRPC and used Responsivity varied between 0
Ratio of Responsivity from BRPC and used Responsivity varied between – with a mean of (Instr. 5-14)
Least scatter: Ventilated pyranometer with netIR offset correction.
Using netIR offset correction determined from capping did not improve the the calibration results