Full text: Close-range imaging, long-range vision

F. Santel, C. Heipke, S. Kónnecke, H. Wegmann 
Institute for Photogrammetry and GeoInformation, University of Hannover, 
Nienburger Str. 1, 30167 Hannover, Germany 
(santel, wegmann, heipke)@ipi.uni-hannover.de 
Inter-Commission (IC), Working Group V/III 
KEY WORDS: Matching, Sea Surface Reconstruction, Video 
Surf zone processes are in the focus of wave research with key words like wave breaking, wave runup and wave overtopping. For 
coastal management tasks numerical models of the sea surface are required. To serve this purpose the sea surface must be determined 
in three dimensions. This paper deals with an automatic method for generating such surfaces based on image matching. For data 
acquisition four synchronised digital video cameras were used. The camera constellation and the expected accuracy are described. 
The determination of the wave surface results from a least squares matching in combination with a region growing algorithm. 
Processing principles for image sequence analysis with and without consideration of the surface movement are shown. The research 
area is a groyne field on a North Sea island in Germany. Due to the progress of the project only first results are presented. 
The protection of the shore and its population from the mighty 
impact of floods and huge waves is one of the most important 
tasks in coastal management. Therefore, the optimisation of 
constructions like dykes or groynes is of high interest in 
research and practice. But the design of their shape and surface 
properties requires detailed information about the waves 
attacking them. In this context the monitoring and prediction of 
the sea state in the surf zone is very important. 
For almost 100 years photogrammetry has been used for the 
recording of sea surfaces (Kohlschütter, 1906). However, wave 
analysis particularly from image sequences using manual 
measurements is very complex and time-consuming. Present 
research and developments with regard to automated matching 
procedures and interpretation of digital images can overcome 
these limitations. This is important for wave analysis, 
considering the fact that photogrammetry is the only highly 
accurate method with a continuous spatial and temporal data 
acquisition. Also, it has to be pointed out that the 
photogrammetric results can be applied for the control and 
verification of numerical models in wave analysis (Strybny et 
al., 2001). 
A number of such numerical wave models to provide time 
dependent wave information already exists. For the control and 
validation of these models spatial and time dependent data are 
needed. Quasi continuous measurement techniques using high 
resolution digital video cameras are applicable for this purpose. 
WAVESCAN is an interdisciplinary project carried out by the 
Institute of Fluid Mechanics (ISEB) and the Institute of 
Photogrammetry and Geolnformation (IPI) of the University of 
Hannover. The intention of this project is the photogrammetric 
acquisition and phase-resolving modelling of surf zones on the 
basis of digital image sequences as well as the combination of 
the measuring and modelling procedures. 
Sites to be studied correspond to typical near shore situations, 
e.g. a groyne field, the near field of a jetty or breakwater. The 
selected test area is a groyne field seawards Norderney Island in 
the coastal waters of the German North Sea. The size is 
approximately 200 by 200 m?. The situation is shown in Figure 
I. The chosen groyne field is a research groyne field of the 
Coastal Research Station, equipped with a number of 
conventional instruments, such as current meters, gauges and 
wave rider buoys. 
Figure 1. Groyne field at Norderney Island 
In order to be useful for other sites as well, the photogrammetric 
data acquisition system must be transferable to different 
conditions. To record areas of arbitrary size for example, the 
system prototype of four cameras (see chapter 3) can be 
extended by adding additional cameras. Also, in terms of 
accuracy different requirements can be fulfilled. 
The requirements on the duration and resolution in time of the 
project vary, depending on the investigated problem. The 

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