Researchers at the CSIR have developed the world's first low element-count three-dimensional (3D) underwater imaging system. The researchers have also built a technology demonstrator that was successfully tested at the underwater test facility of the Institute for Maritime Technology.
The underwater 3D sonar array mechanism is being submerged into the testing facility's pool
The system has been shown to produce world-first images showing detailed feature information, at a level not previously achieved with so few sensor elements. The outputs have attracted the attention of several players, both locally and internationally, in the field of underwater security systems.
The CSIR's Kiri Nicolaides explains how it works: "Conventional imaging systems make use of a two-dimensional planar array of sensors to produce an image of a scene. In the underwater domain the discrete nature of these sensors leads to an extremely high level of complexity and cost. This is because a sensor consisting of, for example, 64 pixels by 64 pixels, would require 4 096 separate sets of receive electronics."
He continues: "In a novel approach for the underwater field, our team developed a range of technology building blocks over a period of three years which can achieve the same image using only 96 sensors. This should make the system much cheaper than 3D underwater imaging systems currently available and, due to its acoustic properties, of a much higher resolution."
The team worked with Professor Andrew Wilkinson of the University of Cape Town's Electrical and Electronic Engineering Department to develop the concept for a 3D imaging sonar that could be realised with a low sensor element count. A large range of technical problems required solving and many technology blocks were integrated together to achieve this unique system.
According to Nicolaides, the development of the system comes from building on the CSIR's experience gained over several years in the field of composite sensor materials. "The team moved up the system hierarchy levels to develop a set of transducer arrays that exhibit high levels of acoustic performance," he says.
Most notable of these is the achievement of very broad frequency bandwidth transmission levels and this aspect alone opened the door for the concept to be developed to its current state of technology readiness. Whereas conventional acoustic transducers have bandwidths close to 20-30 kHz, the team succeeded in realising a ten-fold improvement in bandwidth, producing transmitting transducers with 200 kHz bandwidths.
These broad band transducers were not just made as single element devices but also as multi-element arrays, making use of the composite sensor material properties to be able to pattern electrodes directly to a monolithic structure. This achieves a reduction in device assembly complexity and greatly improves reliability.
The system has been successfully tested in the South African Navy's facilities in Simons Town under the watchful eye of Armscor and Naval personnel. The achievement of images showing object feature details and the resolving of objects placed close together far exceed any system currently available internationally and represent an achievement of significant value to the Navy and other entities concerned with viewing the underwater world around an important facility.