How we are creating near real-time “eyes and ears” from ocean depths
CSIR researchers say underwater drones will soon be able to broadcast high-resolution sonar images of ocean pipelines, hidden underwater mines, subsea cables and even mineral prospects to the surface faster than ever before. They are fine-tuning two critical technologies that make this possible at the CSIR’s underwater testing facility in Pretoria, following a recent sea trial in Simon’s Town.
“One technology is called synthetic aperture sonar (SAS) and the other is, in simple terms, underwater Wi-Fi using sound waves," says Kiri Nicolaides, a lead researcher in sensor systems at the CSIR.
Mounted together on an unmanned underwater vehicle, the two complementary systems will solve a double problem that has limited underwater exploration thus far: poor-quality sonar images of ocean and dam floors taken at a distance and the need to wait for the vehicle to surface to retrieve and process image data into useful maps and high-quality visuals.
The CSIR team is solving the first problem around imaging with specialised signal and image processing algorithms, as well as novel transducers (an electrical component that acts as an underwater antenna to transmit and receive sound waves).
Compared to traditional transducers, these locally developed, wide-bandwidth components give the CSIR’s SAS systems four times more bandwidth to send and receive underwater acoustic waves. More bandwidth means higher data rates with fewer errors, which translates into higher-resolution images.
By arranging a large set of these tiny transducers in an array and using the movement of an underwater vehicle, researchers can synthetically create a much larger “virtual” aperture for sonar imaging. This increases the resolution of images, regardless of whether the target is nearby or far away.
“SAS is like the high definition television version of sonar,” says Josiah Jideani, a senior engineer in the CSIR’s ultrasonics research group. “SAS shines when you’re looking for very small targets or objects that conventional types of sonar won’t be able to detect.”
In the oil and gas industry, for example, SAS can be used for underwater pipeline inspections to check for small leaks or damage. It can also be used for mineral prospecting, geological surveys, marine archaeology, buried underwater mine detection and undersea internet cable monitoring.
The sonar system can be mounted on Autonomous Underwater Vehicles (AUVs) or on a towed underwater platform (a towfish, pulled behind a small boat). The challenge, however, is maintaining a stable speed and straight trajectory, both of which are essential for synthetic aperture processing. Light boats and surface waves introduce motion that must be corrected algorithmically - this is what Jideani’s team is currently working on, in addition to imaging and autofocusing algorithms.
At the CSIR underwater testing facility, the sonar team calibrate the underwater transducers and electronics, fine‑tunes signal processing algorithms and evaluates performance under controlled conditions.
“We take the sensors and load them into the tank,” says Jideani. “There, we’ve got a mechanised gantry that we can control electrically to move along a straight line. As the gantry moves, the sonar pings and receives echoes and we then process that file to generate an image of whatever is on the floor of the tank.”
At the CSIR underwater testing facility, a mechanised gantry (1) moves a submerged synthetic aperture sonar system along a straight line through the water to image a metal board on the floor of the tank (2). The word “CSIR” is spelled out on the board using glass marbles, which serve as small topographical protrusions (3) to be imaged. As the gantry moves, the sonar pings and receives echoes through the water and researchers then process the data to generate an image of the board’s features (4). In the real world, synthetic aperture sonar can be used for underwater pipeline inspections, mineral prospecting, geological surveys, marine archaeology, buried mine detection and undersea internet cable monitoring.
The team also performs ocean and dam tests that introduce uncontrollable variables such as waves, currents, speed changes and platform instability. Data collected during field tests are brought back to the facility, where the team adjusts the algorithms to compensate for real‑world conditions. This iterative cycle between controlled testing and field deployment is central to the technology development process.
In parallel, researchers are tackling the second problem: how to get information back to the surface while a system is still submerged.
“Currently, operators have to wait for an underwater drone (AUVs) to complete its mission and surface again to download the data,” says CSIR senior engineer Elna Niemann. “Seeing snapshots during the mission would provide a lot of savings in terms of time, resources and money.”
She explains that radio waves used for high-speed communication above water typically don’t travel well underwater. “You can’t just submerge a wireless modem underwater and get the same kind of performance you would on land.”
However, she says, sound waves travel very well underwater.
Her team is developing an underwater wireless acoustic communication system or Broadband Underwater Data Communication. This is, in essence, underwater Wi-Fi using sound.
Again, the novelty lies in a specialised ultra-wide bandwidth transducer that provides up to five times more bandwidth for sending sound wave data than commercial acoustic modems.
“We can offer internet-like speeds compared to the commercial offering, which is more in line with telegraph speeds,” she says.
Niemann says the team first tested the algorithms and physics behind the system at the indoor facility at the CSIR in Pretoria. “The underwater testing facility is where it all begins; if it’s not working here, it won’t work anywhere else.”
“Our underwater facility was established over 40 years ago,” says Nicolaides. “It has played a big role in the development of underwater sonar technology at the CSIR and in the broader sonar technology ecosystem in the country.”
He adds that the facility allows researchers to validate technologies to international standards.
Nicolaides, Jideani, Niemann and the rest of the sensors research team headed to Simon’s Town early in 2026 for a sea trial of the SAS and the underwater Wi-Fi prototype.
“While we tested the synthetic aperture sonar at sea, we were also able to test the broadband underwater data communication project in the harbour,” Niemann says. “We were able to achieve very high data throughput, with very good results.”
She says the team will be integrating the two systems, to bring real-time communication and high-resolution imaging together in a single offering for underwater drones.
“Our goal is to provide both the eyes and ears of what the drone is doing underwater,” says Niemann.
The CSIR extends its gratitude for ongoing support for this research to Armscor, the South African Navy and the Department of Defence, especially the Defence Materiel Division and the Directorate Technology Development.
More information about our research, facilities and services: https://www.csir.co.za/what-we-do/manufacturing/sensor-systems
Published 23 March 2026