Campbell CNR4, Instruction Manual, Page: 31 / 70

CNR4 Net Radiometer
21
solar elevation is lower than 10 degrees above the horizon. Errors in the
measurements at these elevations are likely and yield unreliable results. This is
due to deviations in the directional response of the pyranometers.
Albedo = (E lower Pyranometer) / (E upper Pyranometer) (8-3)
In Equation 8-3 , E is calculated according to the Equation 8-1 .
Albedo will always be smaller than 1. Checking this can be used as a tool for
quality assurance of your data. If you know the approximate albedo at your
site, the calculation of albedo can also serve as a tool for quality control of your
measured data at a specific site.
8.5 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)
(8-4)
In Equation 8-4 , E is calculated according to Equation 8-1 .
Net short-wave solar radiation will always be positive. This can be used as a
tool for quality assurance of your measured data.
8.6 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)
(8-5)
In Equation 8-5 , E is calculated according to Equation 8-2 . According to
Equation 8-5 , the terms that contain the sensor body temperature, T, cancel
each other. Therefore, if 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”.
4 / 1
8
10 67 . 5
r Pyrgeomete upper E
e Temperatur Sky






⋅
=
−
(8-6)