Nonlinearity characterization of array spectroradiometers for the solar UV measurements

Applied Optics, 56, pp. 3077-3086, (2017) 
Tomi Pulli, Saulius Nevas, Omar El Gawhary, Steven van den Berg, Janne Askola, Petri Kärhä, 
Farshid Manoocheri, and Erkki Ikonen.

Abstract
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.

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