Apogee SP-214 Manual del usuario - Página 14

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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.

Spectral error for Apogee SP series

pyranometers as a function of solar zenith

angle, assuming calibration at a zenith

angle of 45°.