Kippzonen BSRN Scientific Solar Monitoring System Manual do Utilizador descarregar pdf (Página 28)

3.0 The BSRN Site

3.1 Geographic Location of Site

3.1.1 General Considerations

In selecting sites for the Baseline Surface Radiation Network, the objective is to choose a site

which is representative of a relatively large area (greater than 100 km ) with common features.

The site location should be consistent with the intended purpose for which the observations are

being made. For example, a site which is representative of a unique microclimate within a large

region should not be selected as a site for regional climate observations. In order to achieve this

goal, it is necessary to select sites that are not influenced by small-scale topographic or man-

made features that are unique to the site but not common to the area for which the data are

required. Conversely, if the area is mountainous and contains numerous lakes, then the site

should be selected to reflect the effect of these features.

Great care must be taken in determining the exact placement of a radiation site so that local

influences do not impact the long-term measurement goals of the BSRN. While it is impossible to

predict future developments, 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

determine whether or not future developments, either commercial or residential, will interfere with

the observation site. Some localities have developed multi year land use documents that provide

information on the overall growth pattern of entire regions. These may provide information on

whether or not a long-term monitoring site will be compromised because of excessive

development over the decades following site construction. It is recommended that land use plans

for an area of up to a 20-km radius be reviewed before a final decision is made on the location of

a long-term monitoring station. Local authorities must 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 monitoring laboratory begins. Similarly, BSRN stations should not be built on or

near airports or near a single major 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. The removal of

forests or the change in farming techniques may have significant effects on the albedo and the

amount of natural contaminants. Both of these could mask any climate trends that might be global

or regional in nature.

While changes in the view of the horizon are less critical if they are small, 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, may tower

above the site in future years and force the closure of the observatory. Even trees grow over

decades and can become a significant obstruction, if they cannot be trimmed or removed.

Generally, sites will yield more representative data where the terrain is flat and free from

obstruction. In forested, mountainous, but not built-up areas, moderately sheltered sites which

meet the minimum distances from obstructions can be selected because they will yield data that

are representative of that particular region. Wherever the site is located, it must be representative

of the surrounding region.

In general, BSRN stations should avoid locations that are:

(1) not representative of the surrounding area (approximately 100 km for the local area and

10,000 km for regional representativeness);

(2) near areas that will adversely affect the radiation or ancillary measurements because of

pollution sources, areas of unnatural reflectance or areas where the microclimate is

altered by irrigation or other human modifications;

(3) near major roadways;

(4) near airports;

(5) where there is excessive human or animal traffic;

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Kippzonen BSRN Scientific Solar Monitoring System Manual do Utilizador Página 28

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