Aspects of Lidar Processing in Coastal Areas

The coastline of the North Sea is characterized by a large number of different morphological structures like dikes, dunes, and tidal creeks. Due to the tidal effects and other natural forces like wind the shape, size and position of such objects may change rapidly over time. In order to securely protect shorelines and coastal areas, a permanent monitoring has to be performed. In the past, mainly terrestrial surveys and photogrammetry have been used to obtain information about changes in time. In general these surveys included morphological features like form- and breaklines. Important changes of the monitored objects can be detected by comparing identical morphological features of different time epochs. Unfortunately the terrestrial surveys include a lot of disadvantages like high costs, sometimes very difficult or even impossible to perform and very time consuming. Concerning the aspects of the frequency of surveys and the accessibility to tidal areas Airborne Laserscanning (Lidar) is perhaps more adopted to map changes of morphological objects. However the use of Lidar data gives some new problems, three of them will be shown here together with attempts for their resolving. In many cases especially in flat tidal lands water does not vanish totally during low tide, but areas of water coverage remain and the boundary of tidal land to water can not be extracted accurately from the height data of the Lidar systems. This is especially important, because the Lidar data will be intersected with regular echo sounder data to yield a 3D topography of the coastal area of the German Bight. An approach on how to tackle this problem is shown in this paper. Especially on the islands, but also on the coast side the accuracy of the laser heights sometimes is not very high, because vegetate