Quick Facts
- Institution: National Institute of Geophysics and Volcanology (INGV)
- Industry: Environmental Monitoring / Hydrography / Geospatial Research
- Location: Lago di Conza (Lake Conza), Southern Italy
- Challenge: Bathymetric mapping in turbid, shallow, and debris-filled waters inaccessible to USVs
- Solution: DJI Matrice 600 Pro + Bathymetry Kit by SPH Engineering
- Key Result: LiDAR-validated drone bathymetry with reliable performance in depths below 4-5 m
Background: Institution & Survey Motivation
The National Institute of Geophysics and Volcanology (INGV) undertakes research across Italy’s diverse geophysical landscapes. Lago di Conza (Lake Conza) is an artificial reservoir whose water level changes seasonally, leaving certain areas submerged during wet periods and exposed during dry periods. This unique condition creates an opportunity to reconstruct terrain morphology in both phases.
Traditional bathymetric methods are ineffective and unsafe due to several factors:
- Satellite-derived bathymetry fails due to persistent turbidity.
- Boats/USVs struggle with submerged branches, rocks, and vegetation that restrict access.
- Manual surveys are limited by difficult terrain and safety concerns.
INGV required a method that would ensure safe access, precise georeferencing, and accurate depth-to-elevation conversion across both submerged and exposed states.
The Challenge: Turbidity, Obstacles, and Restricted Accessibility
The reservoir is characterized by very low water visibility, irregular terrain, and dense submerged vegetation. These conditions create hazardous navigation paths and prevent USVs from safely entering many areas.
Additionally, optical methods cannot penetrate the turbid water column, making depth estimation impossible using satellite or photogrammetric techniques.
The challenge was to develop a workflow capable of:
- Capturing accurate depth data in shallow, turbid, debris-rich water
- Maintaining consistent sensor geometry despite submerged obstacles
- Safely reaching narrow and obstructed channels
- Validating underwater measurements with an accurate above-water reference
Only a UAV-based approach could meet all these operational constraints for turbid inland water bathymetry.
The Solution: UAV-Based Echo Sounder Workflow for Inland Bathymetry
INGV deployed a DJI Matrice 600 Pro carrying SPH Engineering’s ECT D052S dual-frequency echo sounder (50 kHz and 200 kHz). Using UgCS Grasshopper mode, the UAV maintained precise altitude above the water surface, ensuring a stable measurement geometry even when flying over branches or debris near the surface.
The workflow included:
- Stable altitude ensured by onboard radar altimetry
- Accurate GNSS PPK corrections using RING network station AV04
- Depth-to-elevation conversion using known probe geometry (2 m cable)
- Dual-frequency data acquisition to compare stability vs detail
During a dry phase of the basin, the same area was surveyed with a UAV-based LiDAR system to create high-resolution DSM and DTM models. These were then directly compared with the underwater echo-sounder profiles collected at 30 checkpoints.
This combined workflow allowed the team to collect consistent underwater and dry-phase datasets, making it possible to directly compare echo sounder measurements with the LiDAR-derived elevation models.
Results: LiDAR-Validated Drone Bathymetry in Complex Inland Waters
LiDAR datasets with 0.1 m resolution served as the benchmark for evaluating underwater measurements. Echo sounder data collected at both 50 kHz and 200 kHz aligned closely with the LiDAR elevation trends across three transects:
- 200 kHz: high detail, more sensitive to vegetation and submerged obstructions
- 50 kHz: less detailed but more stable bottom detection in turbid, debris-filled zones
Both frequencies successfully reproduced the underlying morphology, including slopes, channel features, and terrain transitions. This confirmed that the UAV-based echo sounder solution can reliably map shallow inland water bodies. The UAV platform accessed narrow tributaries, obstructed channels, and debris-filled areas where USVs could not safely operate, demonstrating a critical operational advantage.
Conclusion
The bathymetric survey at Lago di Conza demonstrates that UAV-mounted dual-frequency sonar is a reliable and practical method for inland bathymetry in shallow, turbid, and obstructed inland waters. By validating sonar data directly against high-resolution LiDAR collected during a dry phase, the National Institute of Geophysics and Volcanology proved that UAV bathymetry can achieve dependable results where traditional approaches fail. This workflow offers a safe, flexible, and scientifically grounded solution for inland hydrographic surveys in challenging environments.
Read the full case study: Bathymetry Reconstruction Using a UAV-Mounted Echo Sounder at Lago di Conza
