Buoys located by GNSS and electromagnetic signals enable divers to navigate underwater without harming animals. A head-up display in the mask shows the appropriate routes.

Up to now, underwater navigation for divers has been limited primarily to orientation at distinctive points or compass navigation. Although there are concepts that, similar to a sonar, are intended to enable position determination using acoustic signal sources, these require a high sound pressure level. This affects the ecosystem and causes stress for the local fauna. In the FFG project ScubaPOIs, a team led by Philipp Berglez from the Institute of Geodesy at Graz University of Technology (TU Graz) has now developed a system that uses GNSS-supported buoys that emit electromagnetic signals to enable precise positioning underwater without harming animals. Using a head-up display in their masks, divers can find their way to the desired destinations and back to the dive boat or around restricted areas. In addition, they can always be found in an emergency. In addition to TU Graz, pentamap GmbH, 1st-Relief GmbH, Oxygen Scientific GmbH, Disaster Competence Network Austria and the Austrian Centre for Research Diving were also involved in the project.

Wave propagation in water is biggest challenge

The operating principle of the navigation system combines the precision of satellite navigation with the transmission of electromagnetic signals under water. The buoys are placed in the deployment area and determine their position via GNSS – more precisely via the Galileo High Accuracy Service (HAS). A signal generator in the buoys sends electromagnetic signals to the divers, who carry a receiver the size of a packet of Mannerschnitten (a popular Austrian wafer confection). Since several buoys communicate simultaneously with the divers’ receivers, the position and depth can be determined using the various distance information via trilateration.

“The biggest challenge for us was calculating the propagation of the electromagnetic signals under water in order to obtain the appropriate distance values,” says Philipp Berglez. “The properties of the water, such as salinity, temperature, depth or conductivity, have a major influence here. Due to these diverse and variable influencing factors, modelling the propagation properties under water was particularly challenging.” The research team succeeded in transmitting signals horizontally over 150 metres, but the scientists still see a lot of potential for optimisation when it comes to penetrating greater depths of up to 100 metres.

Several areas of application

The underwater navigation system is useful for divers in a number of application areas. In the tourist sector, they can be used for sport and leisure diving, where diving spots equipped with position buoys would help visitors to find underwater sights. They can see the way there on the head-up display of their masks. As part of the project, the company Oxygen Scientific has already developed a head-up display that is mounted on the mask. The system is also useful in the fields of aquatic ecology, underwater archaeology and underwater waste documentation.

In addition to the development of the underwater navigation system, it was important to the project team that the system – unlike sonar – does not affect wildlife. Test measurements were carried out on golden rainbow trout, which normally react very sensitively to external influences. The fish did not show any abnormal behaviour during measurements with different transmission power and also behaved normally after the end of the measurements. The golden rainbow trout were also unaffected one week, one month and four months after the measurements, which means that delayed negative effects can also be ruled out with a very high degree of probability