A Boxfish ROV from Boxfish Robotics enabled New Zealand commercial diving company Deep Dive Division to inspect a 163-meter tunnel in conditions where conventional visual methods were ineffective.
By combining the ROV with imaging and pipe profiling sonar systems, the team was able to navigate the confined structure and collect inspection data despite near-zero visibility.
Commercial tunnel and pipeline inspections in highly turbid water remain challenging. Visibility is often close to zero, access is constrained, and diver entry may be unsafe or impossible.
Tunnel Inspection Challenge
Before the inspection, little was known about the tunnel’s internal condition, geometry, potential bends, obstructions, or sediment build-up. Water clarity was extremely poor, making camera-based inspection ineffective beyond the entrance area.
Due to the confined environment and unknown internal conditions, diver entry was considered unsuitable for the operation. The inspection therefore required a solution capable of navigating and collecting usable data in complete darkness and near-zero visibility.
Tunnel Inspection Method
The ROV was also equipped with pipe profiling sonar, which captured cross-sectional and spatial measurements of the tunnel interior. This provided data on tunnel geometry, internal alignment, sediment accumulation, and structural variations along the tunnel length.
The combination of imaging sonar for navigation and pipe profiling sonar for measurement enabled the ROV to progress through the tunnel while recording inspection data for post-mission review.
Tunnel Inspection Execution and Data Capture
Using sonar-based navigation, the Boxfish ROV travelled the full tunnel length. Throughout the inspection, sonar data provided situational awareness for controlled movement and vehicle stability within the confined environment.
As the ROV moved through the tunnel, the profiling sonar continuously captured acoustic cross-sections. The Boxfish ROV supports a distance measurement feed that can be used by profiling sonar software to generate a 3D representation of the pipe’s inner surface across the full 163-meter length. The ROV’s distance measurement feed can come from either a thrust-and-drag-based model or a Doppler Velocity Logger (DVL).
Post-Inspection Data Processing
After the inspection, recorded sonar data was processed into a three-dimensional representation of the tunnel interior by combining sonar data with distance measurements and data from the Boxfish ROV’s onboard sensors.
This converted individual sonar profiles, distance measurements, heading, and depth data into a continuous digital model reflecting the tunnel geometry and internal dimensions.
The model showed that one tunnel section had slumped and another section had partially filled with sediment.
3D view of the tunnel. Courtesy of Deep Dive Division.
Tunnel section filled with sediment. Courtesy of Deep Dive Division.
