The measurement procedure

Alpine Airborne Hydromapping is an airborne, laser-based method that can be used to map the configuration of river courses and their floodplains over a wide area and with high spatial resolution. The system is based on a specially developed green laser which, unlike conventional lasers, penetrates water.

The ‘Airborne Hydromapping’ method was developed by the Hydraulic Engineering Unit at the University of Innsbruck in collaboration with the laser companyRIEGL Laser Measurement Systems Gesellschaft m.b.H.as part of a BRIDGE grant from the Austrian Research Promotion Agency (FFG). Based on this surveying method, the University of Innsbruck established a spin-off company of the same name, AHM (Airborne Hydromapping GmbH).

The green laser scanner VQ-820-G used in the measurement process, developed and manufactured by RIEGL, enables the underwater geometry of rivers, streams and lakes to be surveyed to a penetration depth of several metres, depending on the turbidity of the water. The laser point cloud is filtered to classify, amongst other things, the riverbed, vegetation, man-made structures and water levels. High-resolution digital terrain models are then calculated with an elevation accuracy of approximately 5 to 10 centimetres. Flying at an altitude of around 600 metres – which is safe even for the naked eye – a density of up to 40 points per square metre can be achieved with appropriate flight planning.

Schematic illustration of the measurement method. The green laser is partially reflected at the water’s surface, passes through the water column and is then reflected again at the riverbed. The water depth is calculated from the difference in transit time between the first pulse (water surface) and the second pulse (water bottom).

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                 Airborne Hydromapping GmbH        RIEGL Laser Measurement Systems GmbH