Radiometry at the Physikalisch-Meteorologisches Observatorium Davos and World Radiation Centre

Abstract

The Physikalisch-Meteorologisches Observatorium Davos and World Radiation Centre (PMODIWRC) is responsible for the worldwide homogeneity of measurements of the meteorologically important radiation: the <i>short-wave</i> radiation that originates from the sun and is manifested as total and spectral radiation in the direct solar beam and the diffuse radiation scattered by the atmosphere, and the long-wave radiation, which is infrared radiation emitted by the atmosphere and the Earth's surface. The total solar irradiance measurements are performed by electrically calibrated absolute radiometers of high accuracy. Improved methods have to be developed to transfer the scale of irradiance accurately to space to ensure the necessary continuity of solar monitoring programs. Results of such transfers by comparison with highly accurate cryogenic radiometers are presented. For the measurements of the direct solar spectral irradiance, filter radiometers-so-called sun photometers (SPMs)-are used. Highly stable SPMs have been developed at PMOD/WRC to measure the solar spectral irradiance from the ultraviolet to the near infrared. Results from the space experiments are presented, with special emphasis on the problem of degradation. A third field of research is the accurate measurement of the surface radiation budget and the determination of its dependence on the elevation in Alpine regions and on increasing concentration of greenhouse gases. The implementation of a network in the Swiss Alps is described, and some results are presented.