Kipp&Zonen CGR 4 Pyrgeometers - Manual (Page 11)

2.2.4. Installation for shaded measurement of downward long-wave radiation
For amplification of the pyrgeometer signal Kipp & Zonen offers the AMPBOX signal amplifier.
This amplifier will convert the micro-Volt output from the pyrgeometer into a standard 4 – 20 mA signal.
The use of the AMPBOX amplifier is recommended for applications with long cables (> 100m), electrically
noisy environments or data loggers with a current-loop input.
The AMPBOX can be factory adjusted to suit the sensitivity of an individual pyrgeometer to produce a
defined range, typically 4 mA represents -300 W/m², 16 mA represents 0 W/m2 and 20 mA represents
+100 W/m².
2.4. Operation
After completing the installation the pyrgeometer will be ready for operation. The downward atmospheric
long-wave radiation can be calculated with Formula 1 by measuring the detector output voltage Uemf [µV],
the housing temperature T
b
[K], and taking the sensitivity calibration factor S [µV/W/m²] into account.
Formula 1
=Downward atmospheric long-wave radiation [W/m²]
=Net radiation (difference between the downward [W/m²]
longwave radiation emitted from the atmosphere
and the upward irradiance of the CGR 4 detector)
=Upward irradiance of the CGR 4 detector [W/m²]
Note that the net radiation term (U
emf
/ S) is mostly negative, so the calculated downward atmospheric
long-wave radiation is smaller than the detector’s upward irradiance ( ).
This refers to the net radiation within the pyrgeometer, not the ‘net radiation’ as referred to in 2.2.5.
In the Baseline Surface Radiation Network (BSRN) manual (WMO/TD-No.897) an extended formula is
described. This formula corrects for window heating and so called “solar radiation leakage”. Due to the
very low window heating offset and optimal spectral cut-on wavelength, these corrections are not
necessary for the CGR 4.
To be certain that the quality of the data is of a high standard, care must be taken with daily maintenance
of the pyrgeometer. Once a voltage measurement is taken, nothing can be done to retrospectively
improve the quality of that measurement.
During field measurements the pyrgeometer is exposed to varying atmospheric conditions with typical
radiating properties. Therefore we define the two most common conditions as ‘overcast sky’ and ‘clear
sky’, refer to 2.4.1 and 2.4.2 respectively.
Page 11
L
d
=
b
U
emf
S
+ 5.67 • 10
-8
• T
4
L
d
U
emf
S
b
5.67 • 10
-8
• T
4
b
5.67 • 10 -8 • T 4
CGR 4 Manual