This job was carried out in June 2017 for Environment Canterbury with the scope being to survey a 4km length of river and to pick up both the above and below water river bed. The purpose of collecting this data is to assist with gravel change volume analysis.
The aerial survey was carried out using a DJI Phantom 3 UAV, and the depth calibration points were collected using traditional ground survey techniques using a Trimble GPS setup.
Ground control points were placed along both bank of the river in order to assist with georeferencing of the imagery and to allow a detailed terrain model to be built using the Structure From Motion techniques (advanced photogrammetry).
A 3D point cloud was generated and a ground terrain was generated. A comparison between the bed elevation in the point cloud were made with the surveyed bed levels and an adjustment was made in order to allow for the complex refraction processes. The adopted correlation gave an R2 goodness of fit of 0.94. Comparison between the surveyed bed level and the final DEM gave an excellent fit as shown below.
We would love to have more opportunities to explore and develop these techniques further. If you are interested in learning more about these techniques or trialing them at your site, please get in contact with Matthew Gardner.