The World Radiation Center (WRC) has the following terms of reference (Fröhlich et al., 1995):

• Guarantee world-wide homogeneity of meteorological radiation measurements by maintaining the World Standard Group (WSG) which is used to establish the World Radiometric Reference (WRR, Fröhlich, 1978).
• Calibration of meteorological radiation instruments.
• Research and development in radiometry and methods of observation of atmospheric radiation parameters.
• Training of radiation specialists.

The Swiss government offered the World Meteorological Organization (WMO, Geneva) to operate the WRC as a contribution to the World Weather Watch program ( WWW).

Every five years, an International Pyrheliometer Comparison (IPC) is held at PMOD/WRC to transfer the WRR to the participating pyrheliometers in order to ensure world-wide homogeneity of solar radiation measurements. It is chiefly intended for the calibration of absolute radiometers from the Regional Radiation Centers of the six WMO regions. The next IPC(X) will be held in 2010.

The World Radiometric Reference is the measurement standard representing the SI unit of irradiance. It was introduced in order to ensure world-wide homogeneity of solar radiation measurements and is in use since 1980.
The WRR was determined from the weighted mean of the measurements of a group of 15 absolute cavity radiometers which have been fully characterized. It has an estimated accuracy of 0.3%. The WMO introduced its mandatory use in its statutes in 1979.



Definition of the WRR using the results of 15 absolute cavity radiometers. The shaded area represents the ± 0.2% deviation from the WRR (Fröhlich, 1978).

The WRR is determined by a group of absolute cavity radiometers named the World Standard Group (WSG). At the moment, the WSG is composed of 6 instruments: PMO-2, PMO-5, CROM-2L, PACRAD-3, TMI-67814 and HF-18748.

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References

Fröhlich, C., 1977, 'World Radiometric Reference', in: WMO/CIMO Final Report, WMO No. 490, 97-110. (PMOD/WRC intern: 545a)

Fröhlich, C., 1991, History of solar radiometry and the World Radiation Reference, Metrologia 28, 111-115. (PMOD/WRC intern: 650)

Fröhlich, C., Philipona, R., Romero, J., and Wehrli, C., 1995, Radiometry at PMOD/WRC in Davos, Optical Engineering 34, No. 9, p. 2757-2766. (PMOD/WRC intern: 674)