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TOWARDS REMOTE MAPPING
OF ESTUARINE SEDIMENT TYPES AND SALT MARSH VEGETATION
USING HIGH SPECTRAL RESOLUTION
J.M.M. KOKKE
Ministry of Transport, Public Works
and Water Management
Survey Department of Rijkswaterstaat
P.O. Box 5023
2600 GA Delft
The Netherlands
S. VAN ZANTEN
Free University.
Faculty of Biology,
Department of Ecology and Ecotoxocology
De Boelelaan 1087
1081 HV Amsterdam
The Netherlands
ABSTRACT:
Recently two studies were conducted in the estuary of the Westerscheldt to determine whether remotelysensed
remotelysensed spectral data in the optical window offer perspectives to monitor sediment and vegetation in this
highly dynamic area. For both studies use was made of ground truth data on one hand and data of a high
spectral resolution Field spectrometer PS II, the airborne imaging spectrometer casi and of Landsat-TM on the
other. With respect to sediment type mapping with optical remote sensing, analysis of the high spectral
resolution field spectrometer data from different sediment types and correlation with results of gniin size
analysis of corresponding sediment samples in the test site showed that some distinction between sediment
types can be made. Moisture content of the bottom material darkens the colour and is therefore a complica
ting factor. By taking the first order derivative spectra this effect is partly removed. Further evaluation of
some spectral features is planned.
Certain salt marsh vegetation types were spectrally separable but seasonal changes of reflectance were high.
A supervised classification of vegetation based on the TM-data of July gave good results for the largest part
of the area. May and October images were less suitable and did not add any extra information to the Julyclassification.
Julyclassification. Consequently the multi temporal classification gave worse results than the classification of
only the July image.
KEY WORDS: high spectral resolution, field spectrometry, airborne spectrometry, casi, Landsat TM,
sediment type mapping, mapping of salt marsh vegetation, seasonal variation. 1
1 - INTRODUCTION
To be able to make well balanced management decisions to maintain and control the unique tidal area of the
Scheldt in the south-westerly part of the Netherlands there is a need for regular information about a number
of aspects of the region. The estuary forms a natural transition from fresh water via brackish towards salt
water with in all zones vegetated salt marshes, muddy and sandy flats and shallow water, all of them areas
with great potentials for plants and animals. Accumulation and displacement of (fine) sediments are
influenced by a number of factors. Besides hydraulic forces (tides and waves) and the availability of
sediments, for instance salt marsh vegetation stimulates accumulation of fine sediments whereas diatoms
increase critical erosion and stimulate sedimentation of tidal flats. Human activities like dredging and
dumping are important factors too.
In the Westerscheldt there is no natural sand import or export since 1970. Nevertheless the basin hits
been widened by sand mining and dredging activities. Untill now constant dredging has been necessary to
maintain the economically important fairway to Antwerp, thereby disturbing the natural equilibrium.
On the other side the ecological values of the area have to be preserved. The salt marshes in the
brackish-water tidal area present unique ecological values. Dredging activities in the vicinity are a menace to
this vulnerable region. Research results indicate that largely the same measures have to be taken for both
achieving a decrease of dredging activities and for restoration of ecological values. By taking appropriate
dredging and dumping measures and by dereclamation a durable solution can be achieved.
