ELDONET – EUROPEAN LIGHT DOSIMETER NETWORK - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 101

smaller impact on the UV-A irradiances. While the spring UV-B increase can be
observed at all European stations to a different extent, no obvious trend can be extracted
over the four-year measurement period.
There is a weak correlation between the UV-B dose and the ozone concentration
for a given location (correlation coefficient: 0.15). A stronger correlation exists between
reflectivity and measured doses in all measured bands (correlation coefficient UV-B : 0.52,
correlation coefficient UV-A : 0.61, correlation coefficient PAR : 0.67). Reflectivity is
controlled by the cloud cover and other reflecting substances in the atmosphere. Thus,
local weather conditions have a significant influence on the measurements. In Sierra
Nevada, Spain (latitude: 37.67° N) for many days the correlation holds, but significant
differences occur from end of May when fog or clouds cover the mountain top. TOMS
data are only measured once a day so that sudden changes of the reflectivity are not
visible in the data sets.
The correlation between ozone depletion and increasing UV-B irradiances is now
well established. The current UV-B doses are made available to the public e.g. in
Australia, but the awareness of possible health threats of increased UV-B radiation is
still low in Europe. The ELDONET network offers a low-cost and readily available
source of information for local information and prediction. The spectral sensitivity of
the UV-B sensor and filter combination used in the ELDONET instrument closely
resembles the CIE erythema action spectrum so that the erythemally weighted dose can
be easily determined from the UV-B readings of the instruments and from these the
mean erythemal doses (MED). For a Caucasian skin type II one MED is equivalent to
220 J biologically weighted radiation according to the German DIN norm.
Up to now only seven stations measure solar radiation in the water column and
they have not all been active for the whole measuring period, but there are sufficient
reliable data. Penetration of solar radiation into the top layers of the water column is
strongly controlled by the turbidity of the water. In the coastal waters off Helgoland
solar UV-B does not penetrate below 1 m of water, but the penetration is much stronger
in the Atlantic station in Gran Canaria, especially during the winter months when the
transparency is very high.
9. Conclusions and outlook
To the present day, the ELDONET project has been very successful in
monitoring solar radiation. These data are of high quality and even allow to detect
subtle, transient changes in the light climate. One of the advantages of the instrument is
the low cost of about 2300 US dollar, so that the number of instruments in the network
can easily be increased. Interested stations are invited to join the network and make their
data available on the central server to the interested scientific community and the public.
Another advantage is that the measured values can be convoluted with a given
biological weighting function.
Work is in progress to develop a computer simulation to predict the irradiances
and doses of solar radiation for each location for the whole day and each day over the
year based on existing models 47-48 . The intention is to automatically compare the
modeled data with the actually measured values. This can be used to alert the user in the
case of significant deviations. This procedure is straight forward for clear days. In the