Siruis and Nimbus submersibles operated by University of Sydney Australian Centre for Field Robotics marine systems designed for undertaking high resolution benthic optical and acoustic imaging work. (Pics: UniSyd)
Scientists considering the variables in the hunt for the stricken submersible Titan and its five passengers near the wreck of the Titanic needed to think through diabolically complex problems.
The US Coast Guard says there is evdience of a debris field on the seabed seabed ‘consistent with the catastrophic loss of the pressure chamber’ and it’s believed all five people aboard are dead.
“Detecting and identifying submarines or submersibles is a challenging task,” says Kutluyil Dogancay, Professorial Lead of STEM at the University of South Australia.
For each possible method of detection, there’s a snag that might complicate its use.
Take one of the more promising methods of detection: sound and sonar.
Dogancay points out that while sound can travel through water well, determining its source is another matter, even if the vessel is being cooperative, and sending back regular ‘pings’.
“Sound pings transmitted by active sonar devices can travel a reasonably long distance underwater. However, when it comes to determining the location of an underwater object of interest from reflected pings, the current technology may fail to provide a good accuracy.”
Even then, acoustic signals suffer from ducting and bending due to the density and salinity of water. Even if the source of a sound beneath the waves was detected, searchers would need to compensate for these distortions.
Beyond the use of sonar, other detection candidates – like radar and GPS – are less useful. As there is no tether between the Titan and its support surface ship, the only way to communicate with or detect it from the surface is through the sea water.
“In the atmosphere, detection is performed by radar and communications are instantaneous thanks to electromagnetic waves [travelling] across long distances [several kilometres],” says Associate Professor Eric Fusil, Director of the Shipbuilding Hub at the University of Adelaide.
“Unfortunately, under the surface, the sea water is blocking propagation very quickly: no radar, no GPS, and spotlight or laser beams are absorbed within a few meters.”
Navigation control would have been difficult.
Professor Sam Drake, co-Director of the Centre for Defence Engineering Research and Training at Flinders University, says “GPS doesn’t work underwater, and even if it did it wouldn’t help.”
What about other methods of detection? Could searchers search for the submarine’s metal hull?
It is possible to detect metal objects using magnetic anomaly detection , according to Drake.
“But that’s usually for big submarines and vessels closer to the surface.”
“I think this boat has a lot of carbon fibre.”
Dogancay says using sonar to locate submersed objects up to three kilometres underwater can be challenging, considering the signal loss and complex environment.
“The best approach would be to employ a remotely controlled undersea unmanned vehicle with active sonar capability to detect reflections from potential objectives and to identify them,” Dogancay says.
“Sea surface scanning by airborne radar and the use of sea surface sonobuoys is definitely helpful.
“However, the coverage will be limited to objects near the sea surface. A search effort combining all of these systems would give the best outcome. Detecting submersed objects such as submarines from airborne platforms has been one of the major research challenges for defence.
“Current systems heavily rely on active and passive sonar, but magnetic anomaly detection [for magnetic objects] and LiDAR [light detection and ranging] will likely gain more prominence in the near future.”
Stefan Williams, is Professor of Marine Robotics at the University of Sydney’s Australian Centre for Field Robotics and leads the Marine Systems Australia’s Integrated Marine Observing System Autonomous Underwater Vehicle Facility.
He says his submersibles like Sirius and Nimbus (see video above) have transponders capable of sending small data packets to the surface but it won’t provide visual real time images.
“We focus on the use of Autonomous Underwater Vehicles,” Williams says.
“The main focus of our work is on coastal marine environments down to two or three hundred metres. We do have a vehicle capable of workingt at a thousand metres depth.”
Williams points out there is no light under water. “The light attenuates, bounces off the water and scatters out, and not a lot of optical energy gets down to what you are trying to look at so you cant see it.
When it comes to these challenges, Drake says: “We’re stuck…the physics doesn’t change.”