Array spectroradiometers are attractive alternatives to scanning spectroradiometers in solar ultraviolet measurements. However, the measurement of solar spectral irradiance imposes stringent requirements for the linearity of the instruments. In this article, two array spectroradiometers were characterized for nonlinearity. Significant nonlinearities, in excess of 10%, as a function of analog-to-digital converter counts were discovered. Additional nonlinearities as a function of integration time were observed at very long integration times. No clear residual nonlinearity as a function of spectral irradiance was witnessed despite the characterization spanning four orders of magnitude of spectral irradiance. The characterizations were carried out with three measurement setups that are briefly compared.
We have developed an SI-traceable narrow-band tunable radiance source
based on an optical parametric oscillator (OPO) and an integrating
sphere for the calibration of spectroradiometers. The source is
calibrated with a reference detector over the ultraviolet/visible
spectral range with an uncertainty of
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