This case study is based on the scientific article Ruols et al. (2023), from the CRAG group of the University of Lausanne.
Background
The Otemma Glacier in the Swiss Alps is a temperate valley glacier approximately 7 kilometers long, with an average annual retreat of 32 meters observed between 1973 and 2010. Its ablation zone, located below the equilibrium line, is particularly vulnerable to increased air temperatures, which accelerate surface melt and affect ice structure. Prior GPR surveys in the region were conducted on foot and limited in scope due to dangerous surface conditions such as crevasses and unstable moraines. A 2017 ground-based GPR study near the glacier snout identified major subglacial channels, but its extent was constrained by safety concerns and low data acquisition speed. A large collapse in 2018 highlighted the urgency of understanding internal glacier conditions.
To increase spatial coverage while maintaining safety, researchers from the University of Lausanne’s CRAG group collaborated with Utsi Electronics Ltd. and SPH Engineering to develop a drone-based GPR system specifically adapted to alpine glacier environments.
Challenges
The survey of Otemma Glacier involved the following constraints:
Hazardous terrain. Steep moraines, hidden crevasses, and variable ice surfaces increased the risk of on-foot data collection.
Survey efficiency. Traditional methods allowed only limited ground coverage, failing to capture the full extent of subglacial features.
Environmental limitations. Rapid melting and surface instability restricted survey durations, complicating time-lapse (4D) monitoring efforts.
Cost and resolution trade-offs. Helicopter-based surveys covered more ground but lacked the granularity required to identify smaller subglacial channels and ice-bed interfaces.
Faced with these constraints, the research team turned to drone-based GPR to map the glacier's internal structure.
Solution
The drone-based GPR system was engineered to address these issues through system design and automated flight control:
- Compact and lightweight design. A 2.2 kg payload, compatible with the DJI M300 RTK drone, extended flight durations and minimized logistical constraints.
- Enhanced penetration capabilities. Equipped with a custom-made 80-MHz antenna, the system can penetrate glacier ice to depths exceeding 100 meters.
- High-density data acquisition. The system is capable of recording 14 traces per second with 24-bit resolution.
- True Terrain Following (TTF). Integrated with SPH Engineering's TTF system, the drone maintains a consistent altitude over variable glacier surfaces. This was critical in the Otemma survey, where uneven terrain could compromise data quality and drone stability.
- Precision GPS tracking. Differential GPS ensures sub-centimeter accuracy along survey lines.
Results
Using the drone-based GPR system, the team mapped 462 parallel profiles at 1-m spacing over a total of 112 line-km in just four days. A 3D data cube generated from this dataset visualized the internal glacier structure with clarity, highlighting key englacial and subglacial features. The resulting 3D data revealed subglacial channels, englacial features, and clearly defined bedrock interfaces.
The UAV platform eliminated the need for personnel on unstable glacier surfaces, reducing safety risks. The True Terrain Following (TTF) system allowed the drone to maintain a constant height even above crevasses and steep formations, preserving data consistency across the full extent of the survey grid. High spatial resolution and precise flight reproducibility enabled repeat surveys, supporting time-lapse (4D) analysis of glacier change.
Conclusion
The drone-based GPR system delivered high-resolution 3D and 4D datasets with minimal field time and no operator exposure at Otemma Glacier. Combining UAV mobility, deep-penetration radar, and True Terrain Following, the system provided a safer and more productive alternative to traditional glacier surveys. Future refinements will expand its role in glaciological monitoring.
Click here to learn more about Bastien Ruols’ work.
Reference: Ruols B, Baron L, Irving J. Development of a drone-based ground-penetrating radar system for efficient and safe 3D and 4D surveying of alpine glaciers. Journal of Glaciology. 2023;69(278):2087-2098. doi:10.1017/jog.2023.83. Read the full report.