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| Titel |
Measurements on pointing error and field of view of Cimel-318 Sun photometers in the scope of AERONET |
| VerfasserIn |
B. Torres, C. Toledano, A. Berjón, D. Fuertes, V. Molina, R. Gonzalez, M. Canini, V. E. Cachorro, P. Goloub, T. Podvin, L. Blarel, O. Dubovik, Y. Bennouna, A. M. Frutos |
| 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. 8 ; Nr. 6, no. 8 (2013-08-30), S.2207-2220 |
| Datensatznummer |
250085050
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| Publikation (Nr.) |
 copernicus.org/amt-6-2207-2013.pdf |
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| Zusammenfassung |
| Sensitivity studies indicate that among the diverse error sources of
ground-based sky radiometer observations, the pointing error plays an
important role in the correct retrieval of aerosol properties. The accurate
pointing is specially critical for the characterization of desert dust
aerosol. The present work relies on the analysis of two new measurement
procedures (cross and matrix) specifically designed for the evaluation of the
pointing error in the standard instrument of the Aerosol Robotic Network (AERONET), the
Cimel CE-318 Sun photometer. The first part of the analysis contains a
preliminary study whose results conclude on the need of a Sun movement
correction for an accurate evaluation of the pointing error from both new
measurements. Once this correction is applied, both measurements show
equivalent results with differences under 0.01° in the pointing error
estimations. The second part of the analysis includes the incorporation of
the cross procedure in the AERONET routine measurement protocol in order to
monitor the pointing error in field instruments. The pointing error was
evaluated using the data collected for more than a year, in 7 Sun photometers
belonging to AERONET sites. The registered pointing error values were
generally smaller than 0.1°, though in some instruments values up to
0.3° have been observed. Moreover, the pointing error analysis shows
that this measurement can be useful to detect mechanical problems in the
robots or dirtiness in the 4-quadrant detector used to track the Sun.
Specifically, these mechanical faults can be detected due to the stable
behavior of the values over time and vs. the solar zenith angle. Finally, the
matrix procedure can be used to derive the value of the solid view angle of
the instruments. The methodology has been implemented and applied for the
characterization of 5 Sun photometers. To validate the method, a comparison
with solid angles obtained from the vicarious calibration method was
developed. The differences between both techniques are below 3%. |
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