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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 10, issue 3 | Copyright
Atmos. Meas. Tech., 10, 1181-1190, 2017
https://doi.org/10.5194/amt-10-1181-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 22 Mar 2017

Research article | 22 Mar 2017

An automated method for the evaluation of the pointing accuracy of Sun-tracking devices

Dietmar J. Baumgartner1, Werner Pötzi1, Heinrich Freislich1, Heinz Strutzmann1, Astrid M. Veronig1,2, and Harald E. Rieder3,2,4 Dietmar J. Baumgartner et al.
  • 1Kanzelhöhe Observatory for Solar and Environmental Research (KSO), University of Graz, Treffen, Austria
  • 2Institute for Geophysics, Astrophysics and Meteorology/Institute of Physics (IGAM/IP), University of Graz, Graz, Austria
  • 3Wegener Center for Climate and Global Change (WEGC), University of Graz, Graz, Austria
  • 4Austrian Polar Research Institute (APRI), Vienna, Austria

Abstract. The accuracy of solar radiation measurements, for direct (DIR) and diffuse (DIF) radiation, depends significantly on the precision of the operational Sun-tracking device. Thus, rigid targets for instrument performance and operation have been specified for international monitoring networks, e.g., the Baseline Surface Radiation Network (BSRN) operating under the auspices of the World Climate Research Program (WCRP). Sun-tracking devices that fulfill these accuracy requirements are available from various instrument manufacturers; however, none of the commercially available systems comprise an automatic accuracy control system allowing platform operators to independently validate the pointing accuracy of Sun-tracking sensors during operation. Here we present KSO-STREAMS (KSO-SunTRackEr Accuracy Monitoring System), a fully automated, system-independent, and cost-effective system for evaluating the pointing accuracy of Sun-tracking devices. We detail the monitoring system setup, its design and specifications, and the results from its application to the Sun-tracking system operated at the Kanzelhöhe Observatory (KSO) Austrian radiation monitoring network (ARAD) site. The results from an evaluation campaign from March to June 2015 show that the tracking accuracy of the device operated at KSO lies within BSRN specifications (i.e., 0.1° tracking accuracy) for the vast majority of observations (99.8%). The evaluation of manufacturer-specified active-tracking accuracies (0.02°), during periods with direct solar radiation exceeding 300Wm−2, shows that these are satisfied in 72.9% of observations. Tracking accuracies are highest during clear-sky conditions and on days where prevailing clear-sky conditions are interrupted by frontal movement; in these cases, we obtain the complete fulfillment of BSRN requirements and 76.4% of observations within manufacturer-specified active-tracking accuracies. Limitations to tracking surveillance arise during overcast conditions and periods of partial solar-limb coverage by clouds. On days with variable cloud cover, 78.1% (99.9%) of observations meet active-tracking (BSRN) accuracy requirements while for days with prevailing overcast conditions these numbers reduce to 64.3% (99.5%).

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In this work we present KSO-STREAMS (KSO-SunTRackEr Accuracy Monitoring System), a platform-independent, fully automated, and cost-effective system to evaluate the pointing accuracy of Sun-tracking devices as well as its application at the Kanzelhöhe Observatory (KSO) Austrian radiation monitoring network (ARAD) site and to the results from a 15-week evaluating period.
In this work we present KSO-STREAMS (KSO-SunTRackEr Accuracy Monitoring System), a...
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