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| Titel |
Improvement to the PhytoDOAS method for identification of coccolithophores using hyper-spectral satellite data |
| VerfasserIn |
A. Sadeghi, T. Dinter, M. Vountas, B. B. Taylor, M. Altenburg-Soppa, I. Peeken, A. Bracher |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1812-0784
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| Digitales Dokument |
URL |
| Erschienen |
In: Ocean Science ; 8, no. 6 ; Nr. 8, no. 6 (2012-11-30), S.1055-1070 |
| Datensatznummer |
250006017
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| Publikation (Nr.) |
 copernicus.org/os-8-1055-2012.pdf |
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| Zusammenfassung |
| The goal of this study was to improve PhytoDOAS, which is a new retrieval
method for quantitative identification of major phytoplankton functional
types (PFTs) using hyper-spectral satellite data. PhytoDOAS is an extension
of the Differential Optical Absorption Spectroscopy (DOAS, a method for
detection of atmospheric trace gases), developed for remote identification of
oceanic phytoplankton groups. Thus far, PhytoDOAS has been successfully
exploited to identify cyanobacteria and diatoms over the global ocean from
SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric
CHartographY) hyper-spectral data. This study aimed to improve PhytoDOAS
for remote identification of coccolithophores, another functional group of
phytoplankton. The main challenge for retrieving more PFTs by PhytoDOAS is to
overcome the correlation effects between different PFT absorption spectra.
Different PFTs are composed of different types and amounts of pigments, but
also have pigments in common, e.g. chl a, causing correlation effects
in the usual performance of the PhytoDOAS retrieval. Two ideas have been
implemented to improve PhytoDOAS for the PFT retrieval of more phytoplankton
groups. Firstly, using the fourth-derivative spectroscopy, the peak positions
of the main pigment components in each absorption spectrum have been derived.
After comparing the corresponding results of major PFTs, the optimized
fit-window for the PhytoDOAS retrieval of each PFT was determined. Secondly,
based on the results from derivative spectroscopy, a simultaneous fit of
PhytoDOAS has been proposed and tested for a selected set of PFTs
(coccolithophores, diatoms and dinoflagellates) within an optimized
fit-window, proven by spectral orthogonality tests. The method was then
applied to the processing of SCIAMACHY data over the year 2005. Comparisons
of the PhytoDOAS coccolithophore retrievals in 2005 with other
coccolithophore-related data showed similar patterns in their seasonal
distributions, especially in the North Atlantic and the Arctic Sea. The
seasonal patterns of the PhytoDOAS coccolithophores indicated very good
agreement with the coccolithophore modeled data from the NASA Ocean
Biochemical Model (NOBM), as well as with the global distributions of
particulate inorganic carbon (PIC), provided by MODIS (MODerate resolution
Imaging Spectroradiometer)-Aqua level-3 products. Moreover, regarding the fact
that coccolithophores belong to the group of haptophytes, the PhytoDOAS
seasonal coccolithophores showed good agreement with the global distribution
of haptophytes, derived from synoptic pigment relationships applied to
SeaWiFS chl a. As a case study, the simultaneous mode of PhytoDOAS has been
applied to SCIAMACHY data for detecting a coccolithophore bloom which was
consistent with the MODIS RGB image and the MODIS PIC map of the bloom,
indicating the functionality of the method also in short-term retrievals. |
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