307 
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 remotely- 
sensed 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 July- 
classification. 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.