Hydrographic surveying of small Alpine rivers
Heine, Erwin and Peter Mayr
The implementation of the EU Water Framework Directive as well as flood protection initiatives require to monitor alluvial plains and the riverbeds morphology not only for large rivers but also for tributaries. In the case of the riverbed monitoring of small rivers, state of the art hydrographic surveying systems, which are used for bathymetry in bays or large rivers, cannot be applied due to the specific topography of small rivers. Narrow stream courses and steep embankments on the one hand and river banks abundantly covered with vegetation on the other hand impedes the use of heavy survey vessels. For instance, accurate real time kinematic (RTK)-GPS positioning is often not guaranteed due to signal disturbance caused by heavy tree canopy or even obstruction of the signal because of the surrounding topography. In this paper a modular hydrographic surveying system for tributary rivers is presented. It is a modular system, which can be easily mounted on almost any boat. The central components of this system are a hybrid positioning unit, a single-beam echo-sounder and a rugged mobile computer. The high accuracy hybrid positioning unit consists of a RTKGPS system and a motorized total station with automatic target recognition (TPS). The primary data source for positioning purposes is the RTKGPS solution (centimeter accuracy). In the case of GPS signal loss the TPS system is set up at the river bench and takes over the positioning of the measuring platform by tracking the 3600 circular prism mounted on the boat automatically. The resulting position is transmitted to the main computer on the boat via radio link every 0.2s. All sensors of this hydrographical surveying system are synchronized by GPS PPS timestamps and the measurements are stored in a central hydrographical data base. Positions as well as depths are visualized on chart plotters onboard the boat in real time. Thus missing data or measurements of bad quality can be detected immediately, which avoids costly error handling and reduces the post-processing needs.
Event: XXIII International FIG Congress : Shaping the change
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