Low-Altitude and High-Speed Terrain Tracking Method for Lightweight AUVs

Abstract

This paper proposes a new method for cruising-type autonomous underwater vehicles (AUVs) to track rough seafloors at low altitudes while also maintaining a high surge velocity. Low altitudes are required for visual observation of the seafloor. The operation of AUVs at low altitudes and high surge velocities permits rapid seafloor imaging over a wide area. This method works without high-grade sensors, such as inertial navigation systems (INS), Doppler velocity logs (DVL), or multi-beam sonars, and it can be implemented in lightweight AUVs. The seafloor position is estimated based on a reflection intensity map defined on a vertical plane, using measurements from scanning sonar and basic sensors of depth, attitude, and surge velocity. Then, based on the potential method, a reference pitch angle is generated that allows the AUV to follow the seafloor at a constant altitude. This method was implemented in the AUV HATTORI, and a series of sea experiments were carried out to evaluate its performance. HATTORI (Highly Agile Terrain Tracker for Ocean Research and Investigation) is a lightweight and low-cost testbed designed for rapid and efficient imaging of rugged seafloors, such as those containing coral reefs. The vehicle succeeded in following a rocky terrain at an altitude of approximately 2 m with a surge velocity of approximately 0.8 m/s. This paper also presents the results of sea trials conducted at Ishigaki Island in 2017, where the vehicle succeeded in surveying the irregular, coral-covered seafloor.

Guidance method of underwater vehicle for rugged seafloor observation in close proximity

“…This method has been implemented in AUV HATTORI (Maki, Noguchi, et al, 2018). Figure 5 and Table 1 show the vehicle's appearance and specification table, respectively.…”

“…Previously, a method was developed that allows an AUV equipped with an MSIS and capable of maintaining an arbitrary attitude to track omnidirectional surfaces (Noguchi & Maki, 2021). This method is an extension of an artificial potential field (APF) algorithm, which calculates the attitude and surge speed references by introducing an APF around obstacles (Maki, Noguchi, et al, 2018; Warren, 1990). The APF, expressed as the sum of the attractive and repulsive potentials calculated based on a forward occupancy grid map (Thrun, 2002), guides the AUV towards the seafloor (attractive potential) and away from obstacles (repulsive potential).…”

Survey of Terrain-Aided Navigation Methods for Underwater Vehicles

“…Terrain-assisted navigation systems have been developed and studied by researchers in many countries as an applied VOLUME 11, 2023 technology in engineering. In 2016, the Institute of Industrial Science of the University of Tokyo built an AUV called the Highly Agile Terrain Tracker for Ocean Research and Investigation (HATTORI) [28], equipped with a scanning sonar for seafloor exploration with a beam frequency of 675 kHz, a maximum range of 100 m, and a beam width of 3 × 30 • . Maki et al [28] successfully tracked 90m of rocky terrain in 130 seconds during the 2016 experiment and 40m of coral reef terrain in 85 seconds during the 2017 experiment in two at-sea trials using this AUV.…”

A Comprehensive Review of Path Planning Algorithms for Autonomous Underwater Vehicles

“…A potential field algorithm along with other algorithms applied to AUV path planning is also discussed in [43]. APF methods are implemented to the obstacles and target points [44] and the resultant field determines the route of an AUV. A cost function has been introduced to evaluate a path and to optimize the path parameters for a minimum value.…”

“…•Generates energy cost optimized obstacle free path •Robust to local minima •Computation complexity is high and difficult to use in high-dimensional problem Predictable APF [42][43][44][45] Time optimal Achieved Low…”