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|
Time-dependent changes in the optical properties of
sediments detected with remote sensing (TideSed)
(Geographic) study area : “Molenplaat” and “Plaat van Valkenisse”,
intertidal mudflats in the Westerschelde estuary
| Plaat van |
NW |
|
NE |
|
| Valkenisse |
Lat |
long |
Lat |
long |
|
|
51.421 |
4.045 |
51.421 |
4.077 |
|
|
SW |
|
SE |
|
|
|
Lat |
long |
Lat |
long |
|
|
51.350 |
4.045 |
51.350 |
4.077 |
| Molenplaat |
NW |
|
NE |
|
| |
Lat |
long |
Lat |
long |
| |
51.469 |
3.947 |
51.463 |
3.972 |
| |
SW |
|
SE |
|
| |
Lat |
long |
Lat |
long |
| |
51.390 |
3.915 |
51.383 |
3.945 |
Science policy testsite (if applicable) :
Satellite imagery used (type and co-ordinates of images
purchased by Science Policy) : airborne hyperspectral images HyMAP
sensor.
Other data :
25 sites were samples with nine spectral measurements and three
sediment samples at each site. The sediment was analysed for grain
size distribution, moisture content, pigments, organic matter
content. The coordinates of each site were measured with a Global
Positioning System (GPS).
Two erosion experiments with the In-Situ-Erosion-Flume were carried
out.
Ten sediment samples were analysed for macrofauna
Digital Elevation Model of the site was available.
Website (with project results): http://www.kuleuven.be/hydr/remote.htm
Pictures illustrating the project: |
Context and objectives (max 14 lines)
| With one of the largest wading bird populations in western Europe,
and several rare habitat types such as freshwater tidal marshes,
the Schelde estuary is a site of international recognition and importance
for nature. The estuary is also a site of heavy industry, and is
an important commercial shipping route. Many of the most important
biogeochemical processes occur on the large areas of soft sediments
which are exposed at low tide. Examples of those processes are the
binding of heavy metals, photosynthesis by microphytobenthos, which
is the primary food source for higher animals, and erosion and deposition
of sediment influenced by biological and physical factors of the
sediments. Hyperspectral VIS, NIR and SWIR reflectances generated
by HyMAP are used to characterize the main intertidal sediment habitat
types. The main objective of this project is to produce synoptic
maps of the materials of interest (MOIs), namely grain size, moisture
content, organic matter content, chlorophyll a, using advanced image
analysis techniques and an extensive field data set. The generation
of value-added products like maps of ecotopes, primary production
and erodibility for the end-users is an additional objective. Originally,
the detection of time-dependent changes of the sediments was also
envisaged, since many parameters change during a tidal cycle. Exceptional
circumstances prohibited to do the planned second, third and fourth
overpass for data acquisition during the tidal cycle. |
Methodology(max 11 lines)
A consortium consisting of five partners with complementary
skills in remote sensing and coastal zone ecology and physics
was established: Laboratory for hydraulics, KULeuven; Laboratory
for Protistology and Aquatic Ecology, UGent; Marine Biology Section,
UGent; VITO; NIOO-CEME (Nl).
Extensive field work was performed on the day of overflight:
sediment samples, reflectance measurements, and GPS locations.
A database in access was established and the data distributed
via a secured ftp site.
The gathered field data, reflectance measurements and elevation
data were statistically analysed to find correlations between all
the parameters and to improve the performance of vegetation indices
(VI’s). VI’s were tested for their applicability for chlorophyll
a prediction (PAE, NIOO).Supervised and unsupervised classification
procedures were performed by VITO and KUL to obtain maps of the
MOIs. The methodologies and results were compared.
The classification results were combined with elevation data
and models to obtain value-added products. |
Results (max 16 lines)
| Statistical analyse indicated high correlations between grain
size and chlorophyll a, moisture content and chl a, and organic
matter and chl a. High correlations between elevation and these
parameters were also noted.
The best predicting vegetation indices for chl a were the SAVI-index
and the ratio of the reflectances in 665nm and 647nm. Chlorophyll
a and primary productivity maps were established using these indices.
High primary productivity is observed in areas with high chl a
content and higher elevation (higher light availability).
Maps of chl a, grain size, organic matter and moisture content
were produced using supervised classification with accuracies
of 80%, 86%, 87% and 81% respectively. The unsupervised classification
method based on principal component analysis (PCA) could distinguish
classes better than the ISODATA method due to the distinction
of absorption features. Furthermore the PCA method is superior
to the combination of spectral angle mapper with unsupervised
selection of endmembers because of its repeatability, user-friendliness
and robustness. Identical classes were detected in supervised
and unsupervised classification methods, but labelling the classes
was difficult due to limited field information.
An ecotope map was produced based on grain size (potential for
macrofaunal colonisation), chl a (food source), and moisture content
(indication of emersion time). A qualitative erosion resistance
map of the mudflat was produced combining the supervised classification
results and empirical models. The erosion experiments that could
be carried out were not sufficient to obtain a quantitative erosion
resistance map. |
Products and services (if applicable)
Execution
Period: June 2004 – September 2005
Laboratory: Laboratory for Hydraulics, Department of Civil Engineering,
Katholieke Universiteit Leuven |
Discipline (select one or more appropriate disciplines)
Oceans & coasts
Geology & soil |
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