Kipp&Zonen BSRN Scientific Solar Monitoring System - Manual (Page 28)

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3.0 The BSRN Site
3.1 Geographic Location of Site
3.1.1 General Considerations
In selecting sites for the Baseline Surface Radiation N etwork, the objective is to choose a site
which is representative of a relatively large area (greater than 100 km ) with com m on features.
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The site location should be consistent with the intended purpose for which the observations are
being m ade. For exam ple, a site which is representative of a unique m icroclim ate within a large
region should not be selected as a site for regional clim ate observations. In order to achieve this
goal, it is necessary to select sites that are not influenced by sm all-scale topographic or m an-
m ade features that are unique to the site but not com m on to the area for which the data are
required. Conversely, if the area is m ountainous and contains num erous lakes, then the site
should be selected to reflect the effect of these features.
Great care m ust be taken in determ ining the exact placem ent of a radiation site so that local
influences do not im pact the long-term m easurem ent goals of the BSRN. W hile it is im possible to
predict future developm ents, the selection of the location should proceed only after a careful
survey of the area. Before a station is constructed, local planners should be consulted to
determ ine whether or not future developm ents, either com m ercial or residential, will interfere with
the observation site. Som e localities have developed m ulti year land use docum ents that provide
inform ation on the overall growth pattern of entire regions. These m ay provide inform ation on
whether or not a long-term m onitoring site will be com prom ised because of excessive
developm ent over the decades following site construction. It is recom m ended that land use plans
for an area of up to a 20-km radius be reviewed before a final decision is m ade on the location of
a long-term m onitoring station. Local authorities m ust also be consulted to ensure that the site can
be constructed and whether or not any changes are necessary in the official plans before
construction of a m onitoring laboratory begins. Sim ilarly, BSRN stations should not be built on or
near airports o r near a single m ajor industrial source because of the possibility of constructing a
long data set that reflects changes in airport traffic or air pollution control legislation. In rural areas,
care should be taken to ensure that significant land-use changes are not planned. T he rem oval of
forests or the change in farm ing techniques m ay have significant effects on the albedo and the
am ount of natural contam inants. Both of these could m ask any clim ate trends that m ight be global
or regional in nature.
W hile changes in the view of the horizon are less critical if they are sm all, potential changes
should be considered before the location of a site is selected. It m ust be rem em bered that in
urban areas, unless specific allowances are in place, buildings, not yet constructed, m ay tower
above the site in future years and force the closure of the observatory. Even trees grow over
decades and can becom e a significant obstruction, if they cannot be trim m ed or rem oved.
Generally, sites will yield m ore representative data where the terrain is flat and free from
obstruction. In forested, m ountainous, but not built-up areas, m oderately sheltered sites which
m eet the m inim um distances from obstructions can be selected because they will yield data that
are representative of that particular region. W herever the site is located, it m ust be representative
of the surrounding region.
In general, BSRN stations should avoid locations that are:
(1) not representative of the surrounding area (approxim ately 100 km for the local area and 2
10,000 km for regional representativeness); 2
(2) near areas that will adversely affect the radiation or ancillary m easurem ents because of
pollution sources, areas of unnatural reflectance or areas where the m icroclim ate is
altered by irrigation or other hum an m odifications;
(3) near m ajor roadways;
(4) near airports;
(5) where there is excessive hum an or anim al traffic;