A compact underwater robot providing a safer alternative for underwater inspection, search and maintenance

25.10.2023

Divers can face difficult and dangerous conditions when performing essential underwater inspection, search and maintenance. Now a new Remotely Operated Vehicle (ROV) from Switzerland’s Tethys Robotics is providing a much safer alternative.

Find out how a Nortek DVL is being used to complete the navigation solution for this compact robot, while maintaining navigational accuracy in the most challenging underwater conditions.

There are several technical challenges to operating an underwater robot in a lake or river, or offshore in areas of strong tides: the water is often cloudy or murky, making visibility poor, often with leaves and other objects floating or in suspension. The water can be fast flowing, and the bottom can be moving, with sediment, or small stones dragged along by the current.

High-accuracy positioning and inspection in near-zero visibility

Jonas Wüst, now CEO at Tethys Robotics, set out to meet these challenges following a student research project at Eidgenössische Technische Hochschule Zürich (ETH Zurich), a public university in Switzerland.

Jonas Wüst, now CEO at Tethys Robotics, set out to build an autonomous underwater drone following a student research project at Eidgenössische Technische Hochschule Zürich (ETH Zurich), a public university in Switzerland.

Tethys Robotics’ goal was to build an autonomous underwater robot capable of being deployed in rough water with currents of up to 2 m/s. It would need to be capable of high-accuracy positioning and inspection of its immediate environment in near-zero visibility. This required a very accurate underwater navigation solution.

Controlling an underwater robot in swirling currents

If this can be achieved it provides immense advantages to operators, as they can focus on controlling the robot relative to the stationary physical surroundings, without having to worry about trying to control it against swirling currents.

To meet these positioning and navigation needs for their ROV, Wüst and his team equipped their small ROV with a Nortek DVL that meets their specific requirements for achieving bottom tracking and current measurements in the most difficult conditions, securing navigational accuracy.

The DVL, or Doppler Velocity Log, is an acoustic sensor that estimates velocity in water relative to the bottom, using a long pulse along a minimum of three acoustic beams, each pointing in a different direction. 

Achieving bottom tracking for ROVs near a moving riverbed or sea floor

During Tethys Robotics’ first discussions with Nortek, the DVL500 Compact had just been released. This is a 500 kHz DVL in a small form factor – a good match for the requirements of the small ROV the team at Tethys Robotics was working on.

Underwater drone from Tethys Robotics with the DVL500 Compact from Nortek, which facilitates inspection work thanks to reliable positioning.

The DVL500 Compact represents the latest generation in survey-grade DVL technology. By combining the convenient size of the higher-frequency DVL1000 with the superior bottom-tracking range of traditionally larger 500 kHz systems, the DVL500 Compact provides developers of small robotic systems with a reliable, high-performance solution for aiding underwater navigation and control.

“The benefit of the DVL500 Compact for Tethys Robotics was the good penetration of the DVL’s signals through the bottom, river or lakebed,” explains Nortek’s Cristobal Molina, the Senior Sales Engineer working on the project.

Autonomous mapping of submerged infrastructure in strong currents and poor visibility

Their work with the underwater robot has attracted a lot of attention.

“Tethys Robotics is an invaluable partner for developing underwater robots with unique capabilities, such as for autonomous mapping of submerged infrastructures in strong currents and poor visibility,” says Kai Holtmann, Deputy Head of the Swiss Drone and Robotics Centre.

“Their innovative approach allows inspection and exploration works to be carried out at lower cost and, most importantly, without putting divers at risk.”

Tethys Robotics’ underwater drone in Lake Zurich during a harbor inspection.

Good localization and mapping simplify underwater ROV inspections

The success of the unit has opened up a whole new world of applications.

“We are now aiming for applications where we can replace divers, especially in dangerous situations. We recently had our first test with a hydroelectric plant, where the underwater robot had to hold its position relative to the ground in a river flowing at up to 1.2 m/s. It was quite a milestone to see it used in this application, and how easy it is to do inspections if you have good localization and mapping,” Wüst says.

The Tethys ROV can be used from land or from boats without any further deployment equipment.

The technology promises significant benefits for the reliability and safety of important infrastructure.

Professional divers and the Tethys ROV after an underwater inspection operation.

“Wherever you have submerged infrastructure, good reliable inspection is key.”

There are also promising applications for research on submerged structures.

“We’re in talks with archeological teams here in Switzerland,” Wüst adds. 

For more infomation about Nortek, please visit: www.nortekgroup.com