Bathymetry of the river La Lesse in the Grotte de Han

A small portable sonar boat was deployed in the Salle des Armes, where the underground river La Lesse resurfaces in the tourist area of the Grotte de Han. In a cave, there is no GPS reception, so the boat is equipped with an ultra-wideband localisation system (UWB).

 Here you see the boat and on the left and right wall two of the six fixed UWB anchors.

Top view of the Salle des Armes. The river emerges from a siphon located at the bottom of the picture, crosses the chamber and disappears again in another siphon at the top of the picture. There is a tributary flowing to the left.

The resulting bathymetric map of the river. Each dot indicates a depth value.  The deepest points are blue (6.3m).

The 3D model of the river bed based on the lidar (white) and sonar (green) data. The black part at the bottom of the vertical wall is the siphon.

Overlay of the sonar data with a real picture.