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| Titel |
Towards a merged satellite and in situ fluorescence ocean chlorophyll product |
| VerfasserIn |
H. Lavigne, F. D'Ortenzio, H. Claustre, A. Poteau |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 9, no. 6 ; Nr. 9, no. 6 (2012-06-12), S.2111-2125 |
| Datensatznummer |
250007121
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| Publikation (Nr.) |
 copernicus.org/bg-9-2111-2012.pdf |
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| Zusammenfassung |
Understanding the ocean carbon cycle requires a precise assessment of
phytoplankton biomass in the oceans. In terms of numbers of observations,
satellite data represent the largest available data set. However, as they
are limited to surface waters, they have to be merged with in situ
observations. Amongst the in situ data, fluorescence profiles constitute the
greatest data set available, because fluorometers have operated routinely on
oceanographic cruises since the 1970s. Nevertheless, fluorescence is only
a proxy of the total chlorophyll a concentration and a data calibration is
required. Calibration issues are, however, sources of uncertainty, and they
have prevented a systematic and wide range exploitation of the fluorescence
data set. In particular, very few attempts to standardize the fluorescence
databases have been made. Consequently, merged estimations with other data sources
(e.g. satellite) are lacking.
We propose a merging method to fill this gap. It consists firstly in
adjusting the fluorescence profile to impose a zero chlorophyll a
concentration at depth. Secondly, each point of the fluorescence profile is
then multiplied by a correction coefficient, which forces the chlorophyll a
integrated content measured on the fluorescence profile to be consistent
with the concomitant ocean colour observation. The method is close to the
approach proposed by Boss et al. (2008) to correct fluorescence data of a
profiling float, although important differences do exist. To develop and
test our approach, in situ data from three open ocean stations (BATS, HOT
and DYFAMED) were used. Comparison of the so-called "satellite-corrected"
fluorescence profiles with concomitant bottle-derived estimations of
chlorophyll a concentration was performed to evaluate the final error
(estimated at 31%). Comparison with the Boss et al. (2008) method, using
a subset of the DYFAMED data set, demonstrated that the methods have similar
accuracy. The method was applied to two different data sets to demonstrate
its utility. Using fluorescence profiles at BATS, we show that the
integration of "satellite-corrected" fluorescence profiles in
chlorophyll a climatologies could improve both the statistical relevance of
chlorophyll a averages and the vertical structure of the chlorophyll a
field. We also show that our method could be efficiently used to process,
within near-real time, profiles obtained by a fluorometer deployed on
autonomous platforms, in our case a bio-optical profiling float. The
application of the proposed method should provide a first step towards the
generation of a merged satellite/fluorescence chlorophyll a product, as the
"satellite-corrected" profiles should then be consistent with satellite
observations. Improved climatologies with more consistent satellite and in
situ data are likely to enhance the performance of present biogeochemical
models. |
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