Apogee SP-214-SS 소유자 매뉴얼 - 페이지 13

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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).

Silicon-cell pyranometers can still be used to measure shortwave radiation in conditions other than clear sky or

from radiation sources other than incoming sunlight, but spectral errors occur when measuring radiation with

silicon-cell pyranometers in these conditions. The graphs below show spectral error estimates for Apogee silicon-

cell pyranometers at varying solar zenith angles and varying atmospheric air mass. The diffuser is optimized to

minimize directional errors, thus the cosine response graph in the Specifications section shows the actual

directional errors in practice (which includes contributions from the spectral shift that occurs as solar zenith angle

and atmospheric air mass change with time of day and time of year). The table below provides spectral error

estimates for shortwave radiation measurements from shortwave radiation sources other than clear sky solar

radiation.

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.