ELDONET – EUROPEAN LIGHT DOSIMETER NETWORK - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 98

the instrument are 1 mW m -2 for PAR, 0.1 mW m -2 for UV-A and 5 µW m -2 for UV-B.
The error of measurement with respect to a calibrated spectroradiometer is less than
10 % for the UV-B, 5 % for the UV-A and 2 % for the PAR channel.
The specific data of each individual instrument are recorded in a log sheet and
updated during each repair or maintenance. During their lifetime up to now - some
instruments have been in use for over 6 years - the reproducibility was found to be
1.4±1.0 % for the PAR channel, 1.9±1.5% for UV-A and 3.8±3.8% for UV-B based on
a total of 41 instruments, indicating a long-term stability of the instruments 40 .
6. Central server
The central server is installed in Pisa, Italy and is now accessible for everybody
interested in irradiance or dose data (http://www.eldonet.org/). The server is hosted on
an IBM Power/PC and the software consists of two main programs written in Perl 5.
One program is devoted to generate the graphs in GIF format from the submitted data
using the PBMPLUS image manipulation library. Data are sent to the server either by
automatic FTP, by modem or as e-mail attachments. The incoming files are first
checked for plausibility and completeness and then transferred into the directory for the
specific station.
After entering the home page, the user can select a station either on the
interactive map or from the stations list. There is a short description of the ELDONET
project and network as well as for the individual stations. The data are selected from a
calendar and can be viewed in graphical form. The availability of the data is limited to 2
months, but all existing data for the whole lifetime of the project can be downloaded by
FTP in numerical form and then displayed with a data sheet program such as EXCEL.
7. Data
Figure 3 shows a measurement at Ljubljana (Slovenia, 46° N and 15° E) on 11
August 1999. In addition to some scattered clouds, the solar eclipse with an occlusion of
96.6 % at around 12:48 h is clearly visible in all spectral channels. The monthly doses
for the southernmost terrestrial European station of Gran Canaria form a broad peak
during the summer months reaching 320 MJ m -2 in the PAR channel, 48 MJ m -2 in the
UV-A and 1.3 MJ m -2 in the UV-B channel. The UV-B irradiance strongly depends on
the path length of the solar rays through the atmosphere and thus on the solar angle
directly related with the time of the year. The other decisive parameter is the total ozone
column. To eliminate the effect of the changing cloud cover, the ratio of UV-B over
UV-A can be calculated. The UV-B/UV-A ratio peaks in early Autumn rather than in
the Summer which is due to lower ozone values in Autumn, measured by the TOMS
instrument on the NASA Earth Probe satellite, or the predicted ozone concentration
calculated on the basis of Green's model 45 .