3D model rocky slope with sub-centimetre precision

The slope, situated in the region of Albula, in the canton of Grisons, is 500m high and almost 900m long. It is unstable, with movements of approximately one to ten millimetres per day and constant rock falls. The village of Brienz is permanently threatened by the risk of landslides with potentially catastrophic consequences. Because of this, the slope is closely monitored by the Swiss authorities.

Swiss Federal Railways (CFF) does not have any infrastructure in direct proximity to the rocky slope at Brienz. However, since the rate of movement at the site is so exceptional, it provides an opportunity for the CFF to rapidly evaluate new technologies, which it can then use to monitor rocky slopes that represent a potential risk to their infrastructure. 

The assignment, carried out at the beginning of July in the framework of the ‘Natural Hazard’ use case of the In2Smart programme, was the first in a series consisting of capturing LiDAR 3D data to make a model of the slope, roughly every three months. The eventual goal is to make a diachronic analysis of the movements of the slope by comparing different time periods. 

Dr Nicolas Ackermann, Liaison Agent for CFF and Drone Development Engineer explained: "Brienz has all the characteristics of a complex mission, the rocky slope is at high altitude with aerological conditions which make data capture difficult. ALTAMETRIS, with its long experience of using the LIDAR 3D software seemed to me like a natural partner." 

ALTAMETRIS deployed a team composed of a senior drone pilot with 15 years of experience in the civil and military worlds, as well as a topographic geometrist specialised in 3D who was able to parametrise the LiDAR payload and then verify the quality of the acquired data in the field. They deployed the Riegl RICOPTER multi-rotor drone with a mass of 25kg and a span of two metres equipped with a VUX-1 UAV Class 1 type LiDAR. 

This technology allowed them to build a very high density 3D model of the slope with almost 1000 points per square metre in some places. The mission was accomplished in complete safety and without deploying heavy equipment on the ground or by heliporting. 

Olivier Néel, Manager of the Business Unit Inspection at ALTAMETRIS stated: "The RICOPTER is a drone with a robust and reliable aeronautic design, using it follows rigorous protocols and it has to be piloted by highly qualified personnel. The first sets of analysed data have a higher point density than that specified by the customer! This validated the service and we are ready to industrialise the service for other infrastructure operators or authorities with similar needs”. 

The 2D model of the slope has sub-centimetre precision. This allows the maintainer to analyse the slightest movement on the slope, over time, in order to plan specific corrective actions.