A team of researchers has developed a prototype lidar system that utilizes quantum detection technology to obtain 3D images while submerged underwater, marking the first-ever demonstration of such technology. This system’s high sensitivity enables it to capture intricate details even in the extremely low-light conditions typically found underwater.
According to Aurora Maccarone, a Royal Academy of Engineering research fellow from Heriot-Watt University in the United Kingdom and a member of the research team, “This technology could be useful for a wide range of applications. For example, it could be used to inspect underwater installations such as underwater wind farm cables and the submerged structure of turbines. Underwater lidar can also be used for monitoring or surveying submerged archaeological sites and for security and defense applications.”
Capturing 3D images through ocean water can be quite challenging due to the light limitations and the scattering effect of any particles in the water, which can distort the image. However, single-photon detection, a quantum-based technique, allows for high penetration and works even in low-light conditions.
In the journal Optics Express, researchers from Heriot-Watt University and the University of Edinburgh detail their experiments in which they submerged an entire single-photon lidar system in a large water tank. This new demonstration brings the technology closer to practical applications compared to the team’s earlier experiments with underwater single-photon detection, which were conducted under carefully controlled laboratory conditions with the optical setup located outside the water tank, and data analysis was performed offline.
Furthermore, the team implemented new hardware and software advancements that enable the 3D images acquired by the system to be reconstructed in real-time.
According to Aurora Maccarone, a member of the research team and a Royal Academy of Engineering research fellow from Heriot-Watt University in the UK, “Our work endeavors to bring quantum detection technologies to underwater applications, enabling us to capture images of the area of interest in extremely low-light conditions. This will have a significant impact on the use of offshore energy and cable installations, which are utilized by many. Additionally, this technology can enable monitoring without human presence, leading to reduced pollution and a less disruptive presence in the marine environment.”
Faster low-light detection
To create 3D images of obscured objects in highly turbid waters, researchers have developed a lidar system that utilizes quantum detection technology. Conventional lidar systems rely on laser light reflecting off objects and traveling back to the system’s receiver to create images. However, this new approach uses a green pulsed laser source and an array of single-photon detectors to detect ultrafast low light reflections, greatly reducing measurement time in low-light, highly attenuating water.
The approach allows for time-of-flight measurements with picosecond timing resolution, making it possible to resolve millimeter details of targets in the scene. The technology can distinguish photons reflected by the target from those reflected by particles in the water, enabling 3D imaging in highly turbid waters where optical scattering would otherwise ruin image contrast and resolution.
This method requires thousands of single-photon detectors and can produce many hundreds of events per second, making data retrieval and processing for real-time applications challenging. However, researchers have developed algorithms specifically for imaging in highly scattering conditions and used graphics processing unit (GPU) hardware to reconstruct 3D images quickly.
The technique builds on advancements in single-photon detection and image processing from Heriot-Watt University, and the design and fabrication of single-photon avalanche diode detector arrays from the University of Edinburgh. According to Maccarone, this technology will be useful in various applications, including inspecting underwater installations, surveying submerged archaeology sites, and security and defense applications.
