spectroradiometry is less well adapted. Due to their response
characteristics these “broad band” sensors do not measure uniformly
across each waveband, for this reason each sensor is supplied with its
own spectral response curve. This response, normally referred to as the
FWHM (full width at half maximum), should always be given when
presenting data. Data obtained from these sensors cannot be directly
converted to biological damage action spectra.
Measurements from different light sources
UV3p sensors are calibrated under xenon illumination against transfer
standards. These standards are themselves calibrated at
peak
wavelength
against the NPL standard. This in effect means the UV
sensors are calibrated at their peak wavelengths.
Consequently, the UV sensors only measure absolute W.m
-
² correctly if
the source being measured is monochromatic light at the peak
wavelength. This is a shortcoming of any broad band filtered sensor since
no filter will give an absolutely flat spectral response.
A spectroradiometer is the only instrument capable of measuring a
spectral region absolutely since it has a perfect flat spectral response.
To compare the UV sensors to the spectroradiometer, the source being
measured must first be scanned using the spectroradiometer to measure
the defined UV spectral region. The UV sensor is then used to measure
the same source at the same distance. The figure from the UV sensor can
then be corrected to match the figure from the spectroradiometer. Using
this same correction factor will allow any source with the same spectral
output to be measured accurately with the UV sensor.
This procedure must be repeated for sources of different spectral output.
To match the measurement from the spectroradiometer to the UV sensor,
the spectrum measured must be weighted with the response of the UV
sensor.
Glossary
Terms and Units
These terms apply to solar radiation measured with the Delta-T range of
energy sensors (types ES2, UV3p, GS1, GS2, TSL) and the PAR
Quantum Sensor type QS2.
Cosine Corrected
Refers to a sensor that is designed to have a cosine response.
UV3 User Manual 1.1
Appendices
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