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| Titel |
Satellite remote sensing of a low-salinity water plume in the East China Sea |
| VerfasserIn |
Y. H. Ahn, P. Shanmugam, J. E. Moon, J. H. Ryu |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 26, no. 7 ; Nr. 26, no. 7 (2008-07-28), S.2019-2035 |
| Datensatznummer |
250016165
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| Publikation (Nr.) |
 copernicus.org/angeo-26-2019-2008.pdf |
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| Zusammenfassung |
| With the aim to map and monitor a low-salinity water (LSW) plume in the East
China Sea (ECS), we developed more robust and proper regional algorithms
from large in-situ measurements of apparent and inherent optical properties
(i.e. remote sensing reflectance, Rrs, and absorption coefficient of
coloured dissolved organic matter, aCDOM) determined in ECS and
neighboring waters. Using the above data sets, we derived the following
relationships between visible Rrs and absorption by CDOM, i.e.
Rrs (412)/Rrs (555) vs. aCDOM (400) (m−1) and aCDOM
(412) (m−1) with a correlation coefficient R2 0.67 greater than
those noted for Rrs (443)/Rrs (555) and Rrs (490)/Rrs
(555) vs. aCDOM (400) (m−1) and aCDOM (412) (m−1).
Determination of aCDOM (m−1) at 400 nm and 412 nm is particularly
necessary to describe its absorption as a function of wavelength λ
using a single exponential model in which the spectral slope S as a proxy
for CDOM composition is estimated by the ratio of aCDOM at 412 nm and
400 nm and the reference is explained simply by aCDOM at 412 nm. In order
to derive salinity from the absorption coefficient of CDOM, in-situ
measurements of salinity made in a wide range of water types from dense
oceanic to light estuarine/coastal systems were used along with in-situ
measurements of aCDOM at 400 nm, 412 nm, 443 nm and 490 nm. The CDOM
absorption at 400 nm was better inversely correlated (R2=0.86) with
salinity than at 412 nm, 443 nm and 490 nm (R2=0.85–0.66), and this
correlation corresponded best with an exponential (R2=0.98) rather than
a linear function of salinity measured in a variety of water types from this
and other regions. Validation against a discrete in-situ data set showed that
empirical algorithms derived from the above relationships could be
successfully applied to satellite data over the range of water types for
which they have been developed. Thus, we applied these algorithms to a
series of SeaWiFS images for the derivation of CDOM and salinity in the
context of operational mapping and monitoring of the springtime evolution
of LSW plume in the ECS. The results were very encouraging and showed
interesting features in surface CDOM and salinity fields in the vicinity of
the Yangtze River estuary and its offshore domains, when a regional
atmospheric correction (SSMM) was employed instead of the standard (global)
SeaWiFS algorithm (SAC) which revealed large errors around the edges of
clouds/aerosols while masking out the nearshore areas. Nevertheless, there
was good consistency between these two atmospheric correction algorithms
over the relatively clear regions with a mean difference of 0.009 in
aCDOM (400) (m−1) and 0.096 in salinity (psu). This study suggests
the possible utilization of satellite remote sensing to assess CDOM and
salinity and thus provides great potential in advancing our knowledge of the
shelf-slope evolution and migration of the LSW plume properties in the ECS. |
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