Kipp&Zonen BSRN Scientific Solar Monitoring System - Manual (Page 38)

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Figure 3.2. Sim ple post m ount in concrete base .
least affects the data. In the case of a wind m ast, the m ast should be placed where the
obstruction alters the wind field of non-prevailing winds. Distances from growing vegetation should
be increased to account for any future growth.
3.5.2 Instrum ent platform s
Instrum ent stands can be as sim ple as a vertical post holding a single pyranom eter or as com plex
as a raised platform that can hold a large num ber of individual instrum ents and trackers. In all
cases, the platform m ust be stable over long periods of tim e, resisting warping by changes in
tem perature and hum idity, and be im m ovable in strong wind conditions (to within ±0.05°). In m ost
clim ates, wooden platform s should not be used because of their tendency to warp with hum idity
and seasonal changes and because of attack by insects. In tem perate clim ates platform s m ade
of steel or alum inum provide both the necessary stability and durability required for radiation
m easurem ents. In hot clim ates though, these m ay be inappropriate because of extrem e heating
(both with respect to expansion and ease of access due to heating). R einforced concrete, or
concrete and steel structures, when expansion is considered, are probably the optim al m aterials
for the construction of stands, whether they are sim ple posts or com plex platform s.
The base of any post or platform either m ust be firm ly attached to a building or dug into the
ground. In the latter case, the base of the structure should be anchored at a depth below any
m aterial that m ay be subject to heaving due to frost or water. A local or national building code,
where available, will provide excellent inform ation on both the depth to which posts m ust be
im planted and the m eans in which this is best accom plished. If further inform ation is required, a
qualified m echanical or civil engineer fam iliar with the location should be consulted. Figure 3.2
illustrates a typical post installation for a continental site in well drained soil, while Figure 3.3
illustrates the m ore com plex Canadian platform required to elevate the instrum ents above the
local horizon.
Along with the structural integrity of the platform , the height of the platform above the surface m ust
also be carefully considered. As previously m entioned, in built-up areas up-facing sensors can be
located on the top of buildings to overcom e local horizons. In m ore rural areas instrum ents can be
located as close as 1.5 m above the surface. In the latter case, consideration m ust be given for
terrain effects such as blowing or accum ulating sand or snow. W hen instrum ents are placed
higher than approxim ately 1.5 m , a m eans of accessing the instrum ent for cleaning m ust be