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G. Mandlburger:
"Airborne Laser Scanning as geometric basis for Hydraulic Models";
Poster: Egu 2008, Vienna; 2008-04-13 - 2008-04-18; in: "Geophysical Research Abstracts", 10 (2008), ISSN: 1607-7962; Paper ID A-06577, 2 pages.

Due to recent flood events, the definition of endangered or vulnerable areas based on
numerical models of the water flow, has become a topic of highest public interest. The
most influential input for such models is the topography provided as a Digital Terrain
Model of the Watercourse (DTM-W).
In the last years Airborne Laser Scanning (ALS) has become a prime data source for
capturing terrain data of inundation areas. It combines cost efficiency, high degree
of automation, high point densities and good height accuracy. In addition, the laser
signal is able to penetrate the vegetation through small openings. Therefore, ALS is
particularly suitable for deriving precise Digital Terrain Models as geometric basis for
Computational Fluid Dynamic (CFD) models.
To exploit the full information provided by ALS a complete processing chain from the
raw ALS point cloud, via a precise DTM to the well-conditioned hydraulic grid has to
be established. This requires thorough orientation of ALS-strip data, proper filtering
of off-terrain points, correct fusion of ALS and additional river bed data and, finally,
DTM interpolation including filtering of random measurement errors. An advanced
approach for filtering ALS point clouds based on robust interpolation combining geometric
criteria and additional echo attributes derived from full waveform data analysis
is presented, improving the reliability of the classification and the quality of the DTM
especially in low vegetation areas.
The higher point density provided by modern sensors leads to an increased amount of
DTM data. Thus, a direct use of the DTM-W as the geometric basis for CFD models
is impossible. Currently available mesh generators for CFD models basically focus
on physical parameters of the calculation grid like angle criterion, aspects ratio and
expansion ratio. The detailed shape of the terrain as provided by modern ALS data
is often neglected. A data reduction approach based on an adaptive TIN-refinement
is presented, which considers both the physical aspects mentioned above as well as
the preservation of relevant terrain details. The basic idea is to provide a spatially
adaptive data distribution, where the terrain parts being important for the CFD model
are mapped with more details than parts of minor importance.
Finally, practical results of CFD models based on different geometry variants are presented
and discussed. It will be shown that a detailed description of the topography can
be established in CDF models very well, resulting in more realistic flow simulations
and more precise boundaries of potential flooding areas.

http://publik.tuwien.ac.at/files/PubDat_166057.pdf