Apogee Instruments SP-230 Посібник користувача - Сторінка 11
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Multiply this calibration factor by the measured mV signal to convert sensor output to shortwave radiation
-2
in units of W m
:
Calibration Factor (5.0 W m
5.0
Spectral Errors for Measurements with Silicon-cell Pyranometers:
Apogee SP series pyranometers are calibrated under electric lamps in a calibration laboratory. The
calibration procedure simulates calibration under clear sky conditions at a solar zenith angle of
approximately 45°. However, due to the limited spectral sensitivity of silicon-cell pyranometers compared
to the solar radiation spectrum (see graph below), spectral errors occur when measurements are made in
conditions that differ from conditions the sensor was calibrated under (e.g., the solar spectrum differs in
clear sky and cloudy conditions, thus measurements in cloudy conditions result in spectral error because
sensors are calibrated in clear sky conditions).
-2
per mV) * Sensor Output Signal (mV) = Total Shortwave Radiation (W m
*
200
=
Example of total shortwave radiation
measurement with an Apogee SP-110
pyranometer. Full sunlight yields total
shortwave radiation on a horizontal plane at
the Earth's surface of approximately 1000 W
m
-2
. This yields an output signal of 200 mV.
The signal is converted to shortwave
radiation by multiplying by the calibration
factor of 5.0 W m
-2
per mV.
Spectral response of Apogee SP
series pyranometers compared to
solar radiation spectrum at Earth's
surface. Silicon-cell pyranometers,
such as Apogee SP series, are only
sensitive to the wavelength range
of approximately 350-1100 nm,
and are not equally sensitive to all
wavelengths within this range. As a
result, when the spectral content
of solar radiation is significantly
different than the spectrum that
silicon-cell pyranometers were
calibrated to, spectral errors result.
-2
1000
11
)