IMAGE SEQUENCE MATCHING FOR THE DETERMINATION OF
THREE-DIMENSIONAL WAVE SURFACES
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
ASTRACT:
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.
1. INTRODUCTION
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.
2. WAVESCAN
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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