Campbell NR-Lite, Инструкция по эксплуатации, Страница: 9 / 20

NR-LITE Net Radiometer
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FIGURE 3. Approximate Spectral Sensitivity and Solar/F.I.R. Radiation
The upwards facing sensor is calibrated for solar radiation wavelengths. The
following assumptions are made:
•
It is assumed that the downwards facing sensor has the same sensitivity.
However, since the two sensors may not be perfectly symmetrical, this
assumption may not always be true, but any differences are small.
•
It is also assumed that the NR-LITE’s sensitivity is the same for both solar
and infrared radiation.
1.3 Directional/Cosine Response
The measurement of the radiation falling on a surface (also known as
irradiance or radiative flux) is based on two assumptions:
1. The sensor surface is spectrally black - i.e. that it absorbs all radiation
from all wavelengths (see section above).
2. That it has a true field of view of 180°.
These two properties, taken together, with which the net radiometer needs to
comply, are generally known as the ‘cosine response’.
A perfect cosine response will show maximum sensitivity at an angle of
incidence of zero degrees (perpendicular to the sensor surface) and zero
sensitivity at an angle of incidence of 90 degrees (radiation passing over the
sensor surface). At any angle between 0 and 90 degrees the sensitivity should
be proportional to the cosine of the angle of incidence.
Figure 4 shows the behavior of a typical net radiometer. The vertical axis
shows the deviation from ideal behavior, expressed in percentage deviation
from the ideal value.