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Optical Engineering

Fast measurements of solar spectral UV irradiance—first performance results of two novel spectroradiometers
Author(s): Uwe Feister; Anton K. Kaifel; Rolf-Dieter Grewe; Jasmine Kaptur; Oliver Reutter; Michael Wohlfart; Klaus Gericke
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Paper Abstract

Short spectral scan times of preferably less than 1 min in the UV region are an important prerequisite for modern spectroradiometers to reflect short-term solar irradiance radiation variations that can occur as a result of fast changes in cloud cover and/or cloud optical depth. Two different types of fast measuring spectroradiometers for solar UV irradiance are compared in a first field campaign: (1) the UV spectroradiometer on filter model basis (UV-SPRAFIMO) and (2) the modified version of the spectroradiometer SPECTRO 320D by Instrument Systems. The UV-SPRAFIMO instrument combines a filter radiometer with five narrowband (FWHM≈2.0 to 2.7 nm) filters centered at fixed wavelengths in the UV-B and UV-A regions with an advanced neural network-based model. Up to 5 measurements/s can be taken concurrently in the five wavelength channels. After averaging the measurements over preselectable time intervals, the measured irradiances are converted by the neural network model into a full spectrum from 280 to 450 nm at arbitrary wavelength steps (≥0.05 nm). The SPECTRO 320D spectroradiometer consists of a grating double monochromator with a cooled photomultiplier tube (PMT) receiver. The instrument version run by Deutscher Wetterdienst (DWD) is thermostatted and equipped with a Schreder type cosine diffuser as the entrance optics. A spectral scan from 290 to 450 nm with a selected 0.2-nm wavelength step takes less than 30 s. The two spectroradiometers are used in a field campaign at Izana (Tenerife Island) at a height of 2440 m above sea level (ASL) to compare measured spectral and integral values of solar irradiance. Results of that comparison and the instruments' characteristics are discussed. This first field comparison shows that due to the fast measurements regime, cloud effects on the measured spectra can be appreciably reduced. The campaign shows an acceptable agreement between the spectra measured by both instruments. It also reveals some issues for further improvements of the instrument design.

Paper Details

Date Published: 1 April 2005
PDF: 9 pages
Opt. Eng. 44(4) 041007 doi: 10.1117/1.1886816
Published in: Optical Engineering Volume 44, Issue 4
Show Author Affiliations
Uwe Feister, Deutscher Wetterdienst (Germany)
Anton K. Kaifel, Zentrum für Sonnenenergie- und Wasserstoff-Forschu (Germany)
Rolf-Dieter Grewe, Deutscher Wetterdienst (Germany)
Jasmine Kaptur, Zentrum für Sonnenenergie- und Wasserstoff-Forschu (Germany)
Oliver Reutter, Zentrum für Sonnenenergie- und Wasserstoff-Forschu (Germany)
Michael Wohlfart, Zentrum für Sonnenenergie- und Wasserstoff-Forschu (Germany)
Klaus Gericke, Deutscher Wetterdienst (Germany)


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