HYDRO 2016 Paper 7A4
Lutz Christiansen
Schleswig-Holstein, the most northern state of Germany, is placed between the Baltic Sea at the east side and the North Sea at the west side of the state. Due to the fact that the Schleswig-Holstein parts of these water bodies are mainly shallow water areas, the conditions for surveying the coastal areas from the coastal protection structures down to the seafloor are difficult on both seas.
Since 2014 the techniques of LiDAR bathymetry have been used for capturing morphological data. The green light of the bathymetric LiDAR is able to penetrate into the water. The reachable depths depend on the turbidity of the waterbody. Therefore, the power of the systems is described as a factor of Secchi-depths. The local turbidity value multiplied with this factor allows estimating the reachable depth. In Schleswig-Holstein round 2,000 km2 have already been surveyed with these techniques. Bathymetric LiDAR provides the results that are expected in depths as well as in accuracy.
Using these techniques data gaps only occur locally in tideways or low-lying areas, which are needed to be filled by hydrographic surveys. But compared with the bathymetric LiDAR, these surveys have a substantially lower density of points. Hence, it is difficult to merge these data to a morphological model. As a consequence it is necessary to densify the hydrographic data to create a homogeneous model. The mathematical method of Gordon-Coons-patches is suitable for this purpose. The gaps inside the area of hydrographic survey are filled with data points in desired density. The bathymetric information is then calculated using bilinear interpolation.
As result a data set which has a similar point density as the bathymetric LiDAR is created. After the preparation a homogeneous morphological model can be generated by triangulation, based on bathymetric LiDAR on the one hand and hydrographic surveys on the other hand.
|