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| Titel |
Calibrated digital images of Campbell–Stokes recorder card archives for direct solar irradiance studies |
| VerfasserIn |
A. M. Horseman, T. Richardson, A. T. Boardman, W. Tych, R. Timmis, A. R. MacKenzie |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 6, no. 5 ; Nr. 6, no. 5 (2013-05-23), S.1371-1379 |
| Datensatznummer |
250017899
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| Publikation (Nr.) |
 copernicus.org/amt-6-1371-2013.pdf |
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| Zusammenfassung |
| A systematic, semi-automatic method for imaging the cards from the widely used Campbell–Stokes
sunshine recorder is described. We show how the application of inexpensive commercial equipment
and practices can simply and robustly build an archive of high-quality card images and manipulate
them into a form suitable for easy further analysis. Rectified and registered digital images are
produced, with the card's midday marker in the middle of the longest side, and with a temporal
scaling of 150 pixels per hour. The method improves on previous, mostly manual, analyses by
simplifying and automating steps into a process capable of handling thousands of cards in
a practical timescale. A prototype method of extraction of data from this archive is then tested
by comparison with records from a co-located pyrheliometer at a resolution of the order of
minutes. The comparison demonstrates that the Campbell–Stokes recorder archive contains a time
series of downwelling solar-irradiance-related data with similar characteristics to that of
benchmark pyrheliometer data from the Baseline Surface Radiation Network. A universal transfer
function for card burn to direct downwelling short-wave radiation is still some way off and is the
subject of ongoing research. Until such time as a universal transfer function is available,
specific functions for extracting data in particular circumstances offer a useful way forward.
The new image-capture method offers a practical way to exploit the worldwide sets of long-term
Campbell–Stokes recorder data to create a time series of solar irradiance and atmospheric aerosol
loading metrics reaching back over 100 yr from the present day. |
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