Campbell CNR4 Instrukcja Obsługi Pobierz pdf (Strona 27)

CNR4 Net Radiometer

site, the calculation of albedo can also serve as a tool for quality control of your

measured data at a specific site.

7.1.5 Calculation of Net Short-wave Radiation

The net short-wave solar radiation is equal to the incoming (downwelling)

short-wave radiation minus the reflected (upwelling) short-wave radiation.

Net Short-wave Radiation = (E upper Pyranometer)

– (E lower Pyranometer) (7-4)

In the equation above, E is calculated according to Equation 7-1.

Net short-wave solar radiation will always be positive. This can be used as a

tool for quality assurance of your measured data.

7.1.6 Calculation of Net Long-wave Radiation

The net long-wave far infrared radiation is the part that contributes to heating

or cooling of the earth’s surface. In practice, usually the net long-wave far

infrared radiation will be negative.

Net Long-wave Radiation = (E upper Pyrgeometer)

– (E lower Pyrgeometer) (7-5)

In the equation above, E is calculated according to Equation 7-2. According to

Equation 7-5 above, the terms that contain the sensor body temperature, T,

cancel each other. Therefore, if one is only interested in the net long-wave

radiation, instead of separate upper and lower components of the long-wave

radiation, the CNR4 temperature measurement is not required.

The E measured with the pyrgeometer actually represents the irradiance of the

sky (for upward-facing pyrgeometer) or the ground (for downward-facing

pyrgeometer). Assuming that these two, ground and sky, behave like perfect

blackbodies, theoretically, one can calculate an effective “sky temperature” and

an effective “ground temperature”.

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67.5

rPyrgeometeupper E

eTemperaturSky













⋅

−

(7-6)

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1067.













⋅

−

rPyrgeometelower E

eTemperatur Ground

(7-7)

As a rule of thumb, for ambient temperatures of about 20 degrees Celsius, one

can say that one degree of temperature difference between two objects results

in a 5 W/m

exchange of radiative energy (infinite objects):

1 degree of temperature difference = 5 W/m

(rule of thumb)

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