Measuring river level, depth and flow from the air

The challenge

River monitoring usually relies on fixed ground stations or manual sampling. These give point readings, which leave gaps when flow changes quickly, and they are hard to deploy in vegetated or flood-prone areas. On the Rönne Å, dense vegetation, steep banks and unstable ground made many stretches hard to reach.

The drone approach had its own technical hurdles:

• a sonar hanging from a drone tilts with the current and the drone's motion, which upsets depth readings;
• water-penetrating radar picks up early interference from vegetation and surface clutter, so bed reflections are hard to isolate;
• airborne Doppler radar had few precedents in hydrometry and needs stable flight, precise angles and a suitable water surface.

The solution

DJI Matrice 300 RTK drones flew low, automated missions using SPH Engineering's SkyHub and True Terrain Following. They carried:

• Geolux LX-80 radar altimeters for water surface elevation;
• an ECT400S echo sounder for depth;
• a Zond Aero LF ground penetrating radar, used as water-penetrating radar (WPR) to measure depth through vegetation;
• a Geolux RSS-2-300W Doppler radar and a GoPro Hero 8 Black for video-based particle image velocimetry (PIV);
• a DJI Zenmuse L1 for LiDAR terrain models.

Each data stream was logged, georeferenced and synchronised, then projected onto the river cross-sections. Ground instruments were run alongside for point-by-point comparison. Rain on 31 August created flood-like conditions, so the system was also tested under hydrological stress.

The results

• Water level: the radar altimeters measured water surface elevation with under 3 cm vertical precision, in line with GNSS benchmarks.
• Depth: the ECT400S gave stable profiles within 10 cm. The Zond Aero LF saw through vegetation and found bed contours the echo sounders missed. WPR depths were within ±8 cm of ADCP readings.
• Flow: the Doppler radar had a resolution of 7.3 mm/s and stayed within 10 cm/s of OTT MFPro readings. PIV results varied in the vegetated cross-section but agreed well elsewhere.

The dataset has been shared publicly for further research.

Where this applies in India

Contactless, multi-sensor river surveys suit places where ground access is slow or unsafe:

• river gauging and discharge studies on rivers and canals;
• flood monitoring where banks are steep or unstable;
• irrigation canals and channels with heavy weed growth;
• hydrology research at universities and research institutes.

SPH Engineering's bathymetry training is also available through HobiTech.

The equipment, available from HobiTech

Water level	Geolux LX-80 was used. We sell the Geolux LX-80-AB water level measurement kit.
Surface velocity	Geolux RSS-2-300W was used. We sell the Geolux RSS-2-AB water surface velocity measurement kit.
Echo sounder	EchoLogger ECT 400S
Water-penetrating radar	Radar Systems Zond Aero LF
Onboard computer	SkyHub by SPH Engineering with True Terrain Following
Drone and other sensors	DJI Matrice 300 RTK, DJI Zenmuse L1 and GoPro Hero 8 Black were used in this project. Ask us for current compatible drones.

Case study by SPH Engineering, published June 2025, citing Zhou et al. (2025), UAS Hydrometry: Contactless River Water Level, Bathymetry, and Flow Velocity – The Rönne River Dataset, Scientific Data 12, 294. This page summarises it in our own words; the research was carried out by the UAWOS project consortium led by the Technical University of Denmark, not by HobiTech. Read the original case study on SPH Engineering ↗