Campbell CVF4 Especificaciones Pagina 41

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Appendix A. CNR4 Performance and Measurements under Different Conditions
upwellingsignal(downwardfacing)pyrgeometer
30
20
10
0
10
20
30
0:00:00
1:00:00
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5:00:00
6:00:00
7:00:00
8:00:00
9:00:00
10:00:00
11:00:00
12:00:00
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14:00:00
15:00:00
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20:00:00
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23:00:00
0:00:00
Pyrgeometer:Uemf/sensitivity[W/m²] Tempofinstrument[°C]
FIGURE A-3. Clear day for the downward facing pyrgeometer.
It is assumed that when ambient temperature varies, the net far infrared
radiation remains roughly the same, independent of ambient temperature. The
resulting measured values of the pyrgeometers and pyranometers are shown in
columns 4 to 7. These are indicative figures only, they depend strongly on
other circumstances; the pyrgeometer results, of course, change with the sensor
temperature. This is indicated in column 8. During the day, the Pt-100 reading
may rise due to solar heating, up to 10 degrees above ambient temperature.
During the night, the sensor temperature may be lower than the ambient
temperature due to far infrared radiative cooling. The latter two effects do not
influence the end result of the calculations of sky T and ground T. Therefore
they are not taken into account in the table. Actually in column 4 one might
expect to see "0 to -50" for all positions that are showing "0"; in column 5 the
"0" values may in reality be "-20 to +20". The resulting sky temperature is
indicated in column 9. Under cloudy conditions this sky temperature is equal
to ambient temperature. Under clear conditions the sky temperature is lower
than the ambient temperature.
The ground temperature in column 10 is assumed to be equal to the ambient
temperature. In practice it may be higher during the day, due to solar heating.
Ground temperature may be lower than ambient during the night, due to far
infrared radiative cooling. The sky and the ground temperature can be
calculated from the measured values of the sensors using formulas B-1 and B-2
below.
A-3
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