Mobile laser scanning in fluvial geomorphology: mapping and change detection of point bars

Different survey and modeling approaches have been used in fluvial geomorphology. Field measurements for the acquisition of digital terrain models (DTM's) based on traditional approaches are limited in riverine environment because steep river banks, curved point bars and dense vegetation create occluded areas on the sight of survey. In the 1990's, a growing number of studies utilized airborne laser scanning (ALS) for depicting DTM's. More recently, ALS has been applied for more detailed modeling of the environment, such as topographical mapping of forestry/vegetation and infrastructure. It has also been employed in change detection assays, including riverine environments. Most recently, terrestrial laser scanning (TLS) is a more accurate approach for gathering topographical data, e.g. TLS-based DTM's have been employed in measuring landslide bodies, defining the influences of earthquakes, as well as in riverine change detection. Although TLS allows the collection of data at a higher resolution and accuracy than ALS at a lower cost, its areal coverage is considerably more restricted. This limitation can be improved using laser scanning from a mobile platform (mobile mapping system, MMS). In this paper, we demonstrate multi-temporal static TLS and mobile laser scanning (MLS) approaches with BoMMS (boat based mobile mapping system) and CartMMS (cart based mobile mapping system). These survey methods allow us to carry out 3-D mapping of fluvial landforms on a centimeter scale. Multi-temporal data enables accurate change detection and volume calculations of the riverine environment. The accuracy of the BoMMS/CartMMS laser scanning is remarkably better thin ALS, mainly due to the closer scanning distance, higher angular resolution and higher ranging accuracy. The positioning accuracy of the GPS-IMU (Inertial Measurement Unit) system is the most critical part in the error budget. Furthermore, modern digital panoramic imaging technology enables the integrated use of laser scanning data and panoramic images, which further increases the information content of 3-D models in a riverine environment.