ELDONET – EUROPEAN LIGHT DOSIMETER NETWORK - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 92

Aquatic ecosystems are the third area of research 1,19-22 since they account for
about 50 % biomass productivity on our planet. They also play a decisive role in global
carbon fluxes 23 . Due to their essential need for solar energy the primary producers
inhabit the top layers of the water column (the euphotic zone) where they are
simultaneously exposed to solar ultraviolet radiation to which they have been found to
be very sensitive 24-26 .
To estimate the deleterious potential of various wavelength bands of solar
radiation, several networks monitoring solar radiation have been installed or are in the
planning stage. One is the Brewer network using spectroradiometers 27,28 . The
Umweltbundesamt and the Bundesamt für Strahlenschutz have installed
spectroradiometers at four stations in Germany (Offenbach, Schauinsland, Neuherberg,
Zingst), which measure solar radiation at high spectral resolution (0.5 - 5 nm) as well as
the integrated total UV spectrum. A major drawback is that, though in principle the data
should be available to interested scientists, currently there is only limited personnel to
evaluate the data, and the bureaucratic obstacles to actually obtain and use these data are
difficult to overcome.
Other European activities include the SUVDAMA (spectral UV data and
management) project initiated by Seckmeyer (Hannover, Germany) and the
UV-radiative transfer using a set of well-defined spectroradiometers (Webb, Reading,
England). Another project is based on the intercomparison of existing
spectroradiometers (Bais, University of Thessaloniki, Greece).
Some networks specifically target the UV band to follow stratospheric ozone
depletion. The Robertson-Berger (R-B) network has been measuring UV irradiance at
eight stations since 1974 29,31 . The spectral sensitivity (290 - 330 nm) covers the
wavelength range defined for erythemal sensitivity, but this does not coincide with the
CIE (Commission Internationale d`Eclairage) definition of UV-B (280 - 315 nm). There
was a long discussion why the R-B meter network indicated a decrease in solar UV
radiation with time, while satellite data showed a gradual ozone depletion 32-33 .
Eventually, this contradiction was solved by the observation that most R-B meters were
deployed at meteorological stations in the neighborhood of airports, and the increasing
atmospheric pollution due to higher air traffic more than cancelled the increase in UV-B
reaching the surface 34 . Furthermore, a significant temperature sensitivity as well as
aging were found over the years resulting in drifts in wavelength accuracy and
amplitude which offset the factual increases in UV-B 35 .
Other worldwide activities are located in New Zealand 36 , the European Alps 37-38
and the Antarctic 39 . All these projects use spectrally resolved radiation data 27 .
The rationale for the design of the European light dosimeter network
(ELDONET) was to install many stations throughout Europe (and on other continents)
to cover a wide land area. This approach excluded the installation of double
monochromator spectroradiometers because of their considerable costs and demanding
maintenance. Instead, rugged, accurate and reliable, but low-cost, three-channel
dosimeters have been developed with filter functions corresponding to the UV-B
(280 - 315 nm, CIE definition), UV-A (315 - 400 nm) and PAR (photosynthetically
active radiation, 400 - 700 nm). The physically measured values can be convoluted with
any biological filter function (e.g. DNA or plant sensitivity) to determine the biological