Kipp&Zonen BSRN Scientific Solar Monitoring System User Manual

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Alados-A rboledas, L., J. Vida and J.I. Jim éniz, 1988: Effects of solar radiation on the perform ance of

pyrgeometers with silicon domes. Jour. Atm os. O cean. Tech., 5, 666 - 670.

U do, S.O ., 2000: Q uantification of solar heating of the dom e of a pyrgeom eter for a tropical location: Ilorin,
N igeria. Jour. Atm os. O cean. Tech., 17, 995 - 1000.

Philipona, R . C . Fröhlich and C h. Betz, 1995: C haracterization of pyrgeometers and the accuracy of

atmospheric long-wave radiation m easurem ents. Appl. O ptics, 34, 1598 - 1605.

2.2.1.3 Global Radiation

BSRN target uncertainty is 2% (5 W m ). Although the global radiation m ay be determ ined as a

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sum of direct and diffuse irradiance, a direct m easurem ent will be m ade with a ventilated
pyranom eter (the sam e instrum ent type as for diffuse radiation) to provide a basis for quality
control; including instrum ent characterisation and calibration (see Section 8.3 - Calibration
procedures).

T he sam e therm al offset issues associated with the m easurem ent of diffuse irradiance m ust also
be considered for global irradiance. The difference in the m agnitude of the irradiance signals
(global vs. diffuse) reduces the overall relative uncertainty associated with therm al offset for
global irradiance m easurem ents.

Param eters to be acquired are: output of pyranom eter therm opile; pyranom eter body
tem perature. Only the values associated with the calculated irradiance (m ean, m axim um ,
m inim um and standard deviation) are required by BSRN archive. All other raw data should be
archived at the centre responsible for the m easurem ents.

2.2.1.4 Reflected Solar Radiation

This m easurem ent, required at BSRN stations undertaking the "expanded m easurem ent"
program m e, will be done with the sam e type of ventilated pyranom eter as for diffuse and global
radiation. It is suggested that a horizontal shadowband be used to protect the instrum ent dom e
from reflecting direct solar radiation onto the therm opile at low solar elevation. The angle
sustained should be less than 5° (i.e., covering nadir angles 85° to 90°). W ith the exception of
frost on other m aterial on the dom e that would enhance the internal reflection problem , the error
due to internal reflection or the direct beam grazing the therm opile on a level instrum ent is
estim ated to be <1 W m . The m inim um height above the surface for the m easurem ent is 30 m

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so that the observations represents the relfectance of the surrounding area. The actual height of
the downfacing centre should be reported to the archive.

2.2.1.5 Downwelling Infrared Radiation

BSRN target uncertainty is 5% or 10 W m , whichever is greater. Significant evidence suggests

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that a pyrgeom eter with a hem ispheric silicon dom e is negatively im pacted by solar radiation
through dom e heating . The BSRN recognizing this fact determ ined that downward infrared

irradiance should be m easured with a shaded and ventilated pyrgeom eter. Furtherm ore, it noted
that, if using an Eppley PIR, the battery circuit m ust be disconnected and the therm istor
tem peratures directly m easured. It was determ ined that a “m odified PIR" pyrgeom eter (Eppley)
with three dom e tem perature sensors at 45° (but without a battery circuit) was capable of

m easuring downwelling infrared radiation to the target uncertainty. Although not norm ally used in
an unshaded m ode, this m odified instrum ent is designed to m easure infrared radiation in full
sunlight. Furtherm ore, it was recognized that a shaded and ventilated unm odified Eppley
pyrgeom eter could provide nearly the sam e quality of m easurem ent. R ecently, other
m anufacturers have begun producing pyrgeom eters that m ay also be suitable for use in BSRN
stations.