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The problem areas are the reflection characteristics of 
the surface of the sea, mainly topographic and morphological 
in nature. 
For that reason it is possible to make visible sand ripples 
or a rocky bottom. 
But it does not become possible to measure altimetry by stereo 
viewing, since there is too much directional dependence on the 
reflective proporties. 
Altimetry can however be attempted via interferometry construc- 
ting a sonar with 2 neighbouring sound sources and 1 receiver, or 1 
source and 2 neighbouring receivers acting as a coherent system. 
5. Summary 
1) In analyzing remote sensing application in coastal areas one finds, 
that at the first level very simple techniques will suffice; e.g. 
aerial photography taken at the right time. 
2) For some applications digital technology gives better 
results, particularly were quantitative measurement are required. 
This is particularly so in sediment studies and in thermography. 
3) The sonar system is the only one capable of remote sensing 
at depth. 
4) For all applications it is helpful if the image is rectified 
into map form. 
5) Unfortunately image processing by digital means is cumbersome 
and expensive. 
Succesful broad application of digital remote sensing will therefore 
have to go hand in hand with special digital processor hardware 
development, a problem common to all remote sensing applications.