In trying to explain the presence of the errors encountered, several 
error sources could be traced, part of which were of such nature 
that allowed corrections to be made by reprocessing the raw laser 
data. This was true for errors related to the registrations by the 
inertial navigation system (INS) and interaction between laser 
beam and glass plate. Another systematic error source concerned 
the transformation between the WGS'84 co-ordinate system and 
the Netherlands National Reference System, a transformation that 
was not defined with sufficient accuracy. 
The terrain type and dense vegetation cover in some areas caused 
the largest devaluation of accuracy and point density. In these 
areas the laser was simply unable to hit the ground. As a 
consequence, systematic offsets of several tens of centimetres 
were found to be present between laser data and control points. 
As these offsets varied for different control areas, even in the case 
that areas had the same type of vegetation cover, no means were 
at hand to apply a valid correction for them. The terrain relief 
influences the degree in which the laser data can describe the 
terrain surface. With a point density of 1 per 16 m”, small scale 
variations may be missed. Furthermore, sudden changes in the 
terrain surface, like steep dike slopes, were partly filtered out, as 
the filtering program assumed these to be a terrain surface 
anomalies. So here the filtering had been too severe, which once 
again shows that no standard filtering algorithm can be used for 
all parts and that additional terrain information must be added. 
Based on the experienced gained during the 1995 test flights it 
was still concluded that laser scanning is a powerful cost-effective 
technique and that highly accurate data can be generated. 
Therefore, in 1996 new test flights will be performed for the total 
Dutch coast. The results will be compared with the traditionally 
derived photogrammetric coastal profiles. If the accuracy and 
reliability of the laser derived beach profiles are comparable with 
the traditional measurements, laser scanning will be implemented 
from 1997 onwards as an operational procedure to replace the 
photogrammetric production process. This will lead to a cost 
reduction of 1.2 million guilders a year. 
Recently, other attemps at producing DEMs for coastal areas 
using SAR data have been undertaken. Davenport reported, at one 
of the recent EARSeL meetings, his work using multitemporal 
data and tide-heigh data to plot contours in the intertidel region. 
This method actually exploits the non-synchronicity of ERS 
overflights with the tidal cycle. Work is also going on in Dundee 
to examine the use of interferometric SAR (INSAR) to study 
morphological changes in the castal regions and to map changes 
to estuarine sandbanks and saltflats from processed SAR data. 
4. ECOLOGY AND VEGETATION 
4.1 Management problems 
Vegetation information is used by policy makers and managers of 
nature areas as an indicator of the ecological condition of the 
terrain. The species composition and the vegetation structure are 
determined by the site conditions. These conditions are the result 
of action and interaction of all biotic and abiotic factors (viz. 
climatic, geological, geomorphological, hydrological and soil 
conditions and the effect of fauna and human influence) active at 
a particular site. This is called the system (or holistic) approach to 
vegetation. In time this relational complex may change due to 
natural or human induced processes and the vegetation reacts 
accordingly. Hence the role of vegetation maps in monitoring 
programmes is to reveal which processes are active where and, in 
the case of sequential mapping, what is the progression speed of 
these processes. By evaluating the observed changes a manager 
can decide whether it concerns a desirable or undesirable develop- 
ment in relation to the management aims of an area and 
management practices may be adapted accordingly. Remote 
sensing (including aerial photographs) has since long proven to be 
  
  
VEGETATION MAPPING 
VEGETATION CLASSIFICATION 
  
CLASSIFICATION SPATIAL PATTERNS 
  
Ls HIGHER ORDER 
H | VEGETATION TYPE 
  
  
  
NATURE: | suB E 
TARGET TYPE | <—| TARGET TYPE | = 
  
    
  
  
NATURE MANAGEMENT UNITS 
  
  
  
  
[ 
U y 
VEGETATION 
DEVELOPMENT SERIES 
2 
ECOLOGICAL 
INTERPRETATION 
  
  
  
Figure 4: The main components in mapping and monitoring of coastal ecosystems 
16 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B6. Vienna 1996 
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