Retrieval of aerosol optical depth in the visible range with a Brewer spectrophotometer in Athens
A MkIV Brewer spectrophotometer has been operating in Athens since 2004. Direct-sun measurements originally scheduled for nitrogen dioxide retrievals were reprocessed to provide aerosol optical depths (AODs) at a wavelength of about 440 nm. A novel retrieval algorithm was specifically developed and...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2016-04-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | http://www.atmos-meas-tech.net/9/1871/2016/amt-9-1871-2016.pdf |
| _version_ | 1818547958867558400 |
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| author | H. Diémoz K. Eleftheratos S. Kazadzis V. Amiridis C. S. Zerefos |
| author_facet | H. Diémoz K. Eleftheratos S. Kazadzis V. Amiridis C. S. Zerefos |
| author_sort | H. Diémoz |
| collection | DOAJ |
| description | A MkIV Brewer spectrophotometer has been operating in Athens since 2004.
Direct-sun measurements originally scheduled for nitrogen dioxide retrievals
were reprocessed to provide aerosol optical depths (AODs) at a wavelength of
about 440 nm. A novel retrieval algorithm was specifically developed and the
resulting AODs were compared to those obtained from a collocated Cimel filter
radiometer belonging to the Aerosol Robotic Network (AERONET). The series are
perfectly correlated, with Pearson's correlation coefficients being as large
as 0.996 and with 90 % of AOD deviations between the two instruments being
within the World Meteorological Organisation (WMO) traceability limits. In
order to reach such a high agreement, several instrumental factors impacting
the quality of the Brewer retrievals must be taken into account, including
sensitivity to the internal temperature, and the state of the external optics
and pointing accuracy must be carefully checked. Furthermore, the long-term
radiometric stability of the Brewer was investigated and the performances of
in situ Langley extrapolations as a way to track the absolute calibration of
the Brewer were assessed. Other sources of error, such as slight shifts of
the wavelength scale, are discussed and some recommendations to Brewer
operators are drawn. Although MkIV Brewers are rarely employed to retrieve
AODs in the visible range, they represent a key source of information about
aerosol changes in the past three decades and a potential worldwide network
for present and future coordinated AOD measurements. Moreover, a better
understanding of the AOD retrieval at visible wavelengths will also
contribute in improving similar techniques in the more challenging UV range. |
| first_indexed | 2024-12-12T08:13:36Z |
| format | Article |
| id | doaj.art-7330d239d49c4cb9b82495fc4ae4036c |
| institution | Directory Open Access Journal |
| issn | 1867-1381 1867-8548 |
| language | English |
| last_indexed | 2024-12-12T08:13:36Z |
| publishDate | 2016-04-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Measurement Techniques |
| spelling | doaj.art-7330d239d49c4cb9b82495fc4ae4036c2022-12-22T00:31:41ZengCopernicus PublicationsAtmospheric Measurement Techniques1867-13811867-85482016-04-01941871188810.5194/amt-9-1871-2016Retrieval of aerosol optical depth in the visible range with a Brewer spectrophotometer in AthensH. Diémoz0K. Eleftheratos1S. Kazadzis2V. Amiridis3C. S. Zerefos4ARPA Valle d'Aosta, Saint-Christophe, ItalyFaculty of Geology and Geoenvironment, University of Athens, Athens, GreecePMOD/WRC, Davos Dorf, SwitzerlandNational Observatory of Athens, Athens, GreeceBiomedical Research Foundation, Academy of Athens, Athens, GreeceA MkIV Brewer spectrophotometer has been operating in Athens since 2004. Direct-sun measurements originally scheduled for nitrogen dioxide retrievals were reprocessed to provide aerosol optical depths (AODs) at a wavelength of about 440 nm. A novel retrieval algorithm was specifically developed and the resulting AODs were compared to those obtained from a collocated Cimel filter radiometer belonging to the Aerosol Robotic Network (AERONET). The series are perfectly correlated, with Pearson's correlation coefficients being as large as 0.996 and with 90 % of AOD deviations between the two instruments being within the World Meteorological Organisation (WMO) traceability limits. In order to reach such a high agreement, several instrumental factors impacting the quality of the Brewer retrievals must be taken into account, including sensitivity to the internal temperature, and the state of the external optics and pointing accuracy must be carefully checked. Furthermore, the long-term radiometric stability of the Brewer was investigated and the performances of in situ Langley extrapolations as a way to track the absolute calibration of the Brewer were assessed. Other sources of error, such as slight shifts of the wavelength scale, are discussed and some recommendations to Brewer operators are drawn. Although MkIV Brewers are rarely employed to retrieve AODs in the visible range, they represent a key source of information about aerosol changes in the past three decades and a potential worldwide network for present and future coordinated AOD measurements. Moreover, a better understanding of the AOD retrieval at visible wavelengths will also contribute in improving similar techniques in the more challenging UV range.http://www.atmos-meas-tech.net/9/1871/2016/amt-9-1871-2016.pdf |
| spellingShingle | H. Diémoz K. Eleftheratos S. Kazadzis V. Amiridis C. S. Zerefos Retrieval of aerosol optical depth in the visible range with a Brewer spectrophotometer in Athens Atmospheric Measurement Techniques |
| title | Retrieval of aerosol optical depth in the visible range with a Brewer spectrophotometer in Athens |
| title_full | Retrieval of aerosol optical depth in the visible range with a Brewer spectrophotometer in Athens |
| title_fullStr | Retrieval of aerosol optical depth in the visible range with a Brewer spectrophotometer in Athens |
| title_full_unstemmed | Retrieval of aerosol optical depth in the visible range with a Brewer spectrophotometer in Athens |
| title_short | Retrieval of aerosol optical depth in the visible range with a Brewer spectrophotometer in Athens |
| title_sort | retrieval of aerosol optical depth in the visible range with a brewer spectrophotometer in athens |
| url | http://www.atmos-meas-tech.net/9/1871/2016/amt-9-1871-2016.pdf |
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