Underwater navigation of an agile platform using a scanning sonar

Scanning sonars provide real-time imagery of the underwater environment similar to an optical video camera. Most importantly, they can achieve much longer operating ranges than optical systems which suffer from the low-visibility conditions that are common in most underwater environments. These sonars are becoming increasingly small and low-power and can now be deployed from small remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs), as well as being carried by human divers.

Divers, ROVs, and AUVs are very agile and are crucial for carrying out complex underwater tasks, such as inspecting underwater structures for damage and searching for objects. However, to carry out these tasks effectively, requires precise navigation information, e.g., to report the location of damage on a structure or the location of an object of interest. Unfortunately, the satellite navigation systems that we rely on heavily above water are ineffective underwater. Existing underwater solutions include acoustic positioning networks which are expensive, time-consuming to deploy, and have limited range; and / or inertial measurement units (comprised of 3-axis gyroscopes, accelerometers, and magnetic compasses), which suffer from errors that increase with time known as “navigation drift”.

UK SME Picotech Ltd. and Finnish company Alleco are working together to develop a low-cost ultra-portable scanning sonar for divers. This device permits them to “see” their environment in low-visibility conditions as well as extending their range of perception up to 100 m (compared to typical visibility of 0-10 m). Furthermore, it can be operated remotely or autonomously from small ROVs and AUVs.

Picotech are interested in exploring underwater navigation solutions that exploit the data collected by the sonar, effectively using the sonar as a navigation device. The motivation for this is two-fold: 1) to aid inertial sensors, thereby reducing the reliance on deployed acoustic positioning networks and lowering the cost of underwater operations; or 2) to compliment deployed positioning networks and provide enhanced navigation precision. This PhD project aims to achieve this goal by applying advanced signal processing techniques such as micro-navigation, simultaneous localisation and mapping, and data fusion.