Kipp&Zonen BSRN Scientific Solar Monitoring System - Manual (Page 37)

AES G uidlines for C o-operative C lim atological Autostations, Vers ion 2.0, C lim ate Inform ation Branch,
11
C anadian C lim ate Service, Atm ospheric Environment Service, D ownsview, C anada, M 3H 5T 4, 1992. 85
pages.
25
Figure 3.1. Diagram indicating appropriate distances from an obstruction m eteorological
instrum entation (from AES Guidlines for Co-operative Clim atological Autostations, Version
2.0).
radiation are separate, the diffuse and infrared (if shaded) m easurem ent should be the furthest
poleward and slightly elevated, while the direct instrum ent should be closest to the equator and at
the lowest height. The global instrum ent should be centred between these two instrum ents and
higher than the direct instrum ent. The global, diffuse, and infrared instrum ents should be at the
sam e height, with only the shade portion of the diffuse apparatus extending above the height of
the therm opile of the global instrum ent. In the case where the direct and diffuse instrum ents are
set on the sam e tracking platform , the direct beam instrum ent(s) should not interfere with the
horizon of the diffuse instrum ents.
W hen locating instrum ents that m easure upwelling fluxes it is im portant to be able to service these
instrum ents from their poleward direction to reduce ground disturbance that m ay affect direct
reflectance into the sensor from the sun. For exam ple, significant differences in snow albedos can
be observed because of the effects associated with the depressions caused by footsteps near a
downfacing instrum ent on its solar side.
For m eteorological instrum entation, distant horizon problem s are m inim al but interference
between instrum ents is significant. For the m easurem ents of tem perature and pressure, the
Stevenson screen (or equivalent) should be at least twice the distance apart from the height of all
significant objects. These objects should be located poleward of the m easurem ent site so that
shading will not interfere with the instrum ents within the screen. Instrum ents used to m easure
precipitation should be located no closer to the nearest obstruction than four tim es the height of
the obstruction. An instrum ent for the m easurem ent of wind m ust be at least 10 tim es the height of
an object distant from that object. For exam ple, the 10-m etre m ast in Figure 3.1 is located 200 m
11
away from the 20-m etre tall tree. If the instrum entation cannot be located the prescribed distance
from the obstruction, then the instrum ent should be located in a location where the obstruction