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  • Writer's pictureNora Wippermann

UAV flight for the Waterways and Shipping Office West German Canals

The Schwieringhauser Bridge over the Dortmund-Ems Canal has been closed to motorized traffic since September 2020. The bridge is still open to pedestrians and cyclists. The bridge is owned and maintained by the Federal Waterways and Shipping Administration (WSV). The investigations and static calculations to assess the residual stability of the bridge's abutments have shown that the bridge's foundations can no longer bear the traffic loads from vehicle traffic.

Schwieringhauser Bridge

The task

To plan a new bridgehead including a new access via a ramp, the customer needs a digital terrain model (DTM) as well as orthophotos to visualize the existing topography and tree populations.

A total of three areas (Dortmund and Dorsten) with an area that varied between approximately 3,000 and 300,000 square meters were to be recorded. The desired recording method was to fly over the area using a drone with a lidar sensor. The advantage of this measuring technology is that the laser beam can measure both treetops and down to the ground through leaves in dense vegetation. In contrast, a photo drone only provides a view of the nearest object between the drone and the earth's surface.

The challenge

Despite the advantages of the measurement technology, only a small amount of the measurement signal reaches the ground, especially when flying in summer or late summer when the vegetation is dense (leaf cover). As a result, we found gaps in the data material during the evaluation. However, due to the tight time frame, a flight in winter was not possible and the client therefore accepted these losses.

Processing in the office

  • Calculation of a point cloud from drone flight

  • Cleaning up the point cloud so that only ground points are retained (elimination of vehicles, vegetation, existing buildings)

  • Creation / calculation of the digital terrain model (DTM)

  • Smoothing and cleaning the DGM

  • Georeferencing of the data in an official coordinate system and deposit of cadastral data (proof of ownership)

  • Overlay DGM with orthophoto with the advantage of combining photorealistic images in 2D with 3D elevation profiles

Flight data using the example of the Schwieringhauser Bridge

  • approx. 300,000 square meters

  • Flight altitude 70 meters

  • Flight time approx. 45 minutes

  • 710 individual photos for an orthophoto


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