Professor Carl Dorno (founder of PMOD in 1907), who's main interest was in solar radiation and its relation to bioclimatological effects, investigated the very short wavelength part of direct solar radiation already in his early years at Davos. Spectrally resolved measurements were first performed using photochemical and photometrical methods. In honour to his work the shortest solar radiation penetrating to the Earth surface, became the "Dornostrahlung", the spectral part which is nowadays known as solar UV-B radiation. Dorno was a strong advocate of the Cadmiumzell which from 1916 to the thirties was routinely used at Davos for spectrally integrated UV-measurements. The large solar height (seasonal dependency) and altitude dependency of solar UV-radiation was deduced from these measurements among other interesting findings.
Dr. Paul Bener conducted intensive investigations of the UV-radiation field between 1954 and 1976. His spectrophotometric measurements of direct, diffuse and global UV-radiation at Davos, Weissfluhgipfel and Basel, allowed him to investigate the UV part of the solar radiation with regard to solar height, altitude, ozone amount and cloud influence. Bener also performed extensive UV calculations to extrapolate into regions in which measurements could not be performed due to technical or logistical reasons. Assumptions had to be made to cover the full picture for a global UV-climatology. Beners investigations were published in many reports and publications.
From 1975 to 1985 Davos was one of the fourteen stations of the world UV-network which were maintained by the Temple University School of Medicine, Philadelphia, PA, USA. Robertson-Berger type 500 broadband UV-Biometers, which integrate over the human skin erythema action spectrum, were used at these stations. The network was discontinued due to lack of funding.
UV broadband measurements were resumed in 1993 using UV-Biometers from Solar Light CO. which weight the UV radiation to the human skin erythema action spectrum and therefore predominantly measure UV-B radiation.
Long term tests of individually measuring the direct solar - and the diffuse sky component, showed positive results with regard to the accuracy of broadband UV measurements and to the understanding of the radiation field. Direct radiation was measured with a full view angle of 8 degrees whereas the instrument measuring diffuse radiation has a shading disc covering the sun with a full view angle of 8 degrees. An additional UV-Biometer measuring global radiation was used for redundancy and quality control of the measurements.
The UV-A radiation was separately measured with a global Solar Light UV-A bandpass instrument.
Calibration was maintained by periodically comparing UV-Biometers to the SWISS reference instrument using the sun as a source. The SWISS reference instrument took part at the WMO/STUK 1995 intercomparison at Helsinki and was periodically compared to spectroradiometers.
Although this instrumentation was not accurate enough to measure long term trends, it was well suited to establish a UV climatology and to provide the necessary information for UV forecasts and warnings.
Following the long tradition of sunphotometry at PMOD, filter radiometrique techniques were extended to the UV-range. UV Precision Filter Radiometers (UV-PFR) with narrowband interference filters were used to measure UV radiation at fixed wavelength. The final layout of the UV-PFR basically follows the design of the Precision Filter Radiometers (PFR) built at PMOD/WRC for very accurate aerosol optical depth measurements (WORCC). The instrument has four channels, three in the UV-B range with center wavelength at 303, 310 and 319 nanometers and one channel in the UV-A range at 340 nanometers with the respective bandwidths of 1, 2, 2 and 4 nanometers.
UV-PFRs were periodically calibrated against trap-detectors in the laboratory which allow very high accuracy of the order of 0.5% and are therefore well suited for UV trend measurements.
In collaboration with the Swiss Meteorological Institute (SMI/MeteoSwiss), the three component broadband UV-B (direct, diffuse and global) plus UV-A instrumentation was installed on a limited number of RASTA-UV stations in order to build a Swiss national UV network. All stations are additionally equipped with direct, diffuse and global solar shortwave (SW) instruments and a pyrgeometer measuring downwelling longwave (LW) radiation (ASRB) as well as a sunphotometer to measure aerosol optical depth. The Swiss national UV-network is part of the Swiss Atmospheric Radiation Monitoring program (CHARM).
Beside the station at Davos (1610m a.s.l.) two other stations are in operation at Payerne (490m a.s.l.) and on the Jungfraujoch (3580m a.s.l.). Additional stations will be installed later at Locarno-Monti (370m a.s.l.) and Zürich (556m a.s.l.).
PMOD/WRC also equipped a UV research station in the observation and investigation field of the Swiss Federal Institute for Snow and Avalanche Research (SLF) which is located at the vicinity of the Weissfluhjoch at 2540m a.s.l.. At this station additional instruments measure reflected UV-B, UV-A, SW and upwelling LW radiation for albedo investigations.
The four operational stations of the Swiss national UV network provide an interesting vertical profile of the UV radiation field over Switzerland going from 490 to 3580m a.s.l.. The additional stations will allow to investigate UV-radiation in rather urban regions south and north of the Alps.
Routine ozone measurements are made at Arosa which is only 12 km south-west of Davos and about 200m higher. Ozone profiles are routinely measured at Payerne using stratospheric sondes.