Line-of-sight iceberg edge-following using an AUV equipped with multibeam sonar

Abstract

Obtaining 3D information about ice features, like icebergs, are of interest to researchers and offshore operators moving into the Arctic. Icebergs are affected by wind, and ocean currents, and can have unpredictable drift patterns, causing challenges when it comes to mapping objectives. Autonomous underwater vehicles (AUVs) equipped with multibeam echosounders are suitable for obtaining measurements of the underwater geometry of icebergs, but advances in autonomy are needed to map drifting icebergs reliably. This paper details a guidance algorithm for detecting and circumnavigating an iceberg -following the iceberg edge. The guidance scheme is implemented as a state machine, starting in an iceberg detection-mode.Once an iceberg is detected, the AUV will enter a mapping-mode. An edge detection algorithm will determine the position of the edge, and a line-of-sight approach will be used for edgefollowing. A six degree-of-freedom AUV simulator is used to perform a simulation study, to show how AUV dynamics affect the results. The simulation study presented shows the algorithm's effectiveness, both when the iceberg is assumed stationary, and when the iceberg is drifting and rotating with constant velocity.

Mapping the underside of an iceberg with a modified underwater glider

“…A sketch of tracking the desired track, , is shown in Figure where is the estimated iceberg profile, is the cross‐track error, is the trend of the desired track relative to the vehicle heading . We adopt proportional–integral–derivative line‐of‐sight guidance law (Norgren & Skjetne, ) to compute the desired heading, , for trajectory following, which is shown in Equation with , , and being the control gains for the cross‐track error . The current vehicle heading, , is added in Equation since the trend of the desired track is estimated relative to the vehicle from the VOM, but the heading controller in the glider is based on the north–east–down frame.…”

“…There are several advantages to using AUVs for iceberg mapping compared to the existing ship‐based approaches. First, harsh environments have less impact on AUV operations than on ship‐based operations (Norgren & Skjetne, ). Moreover, an AUV‐based iceberg survey has the potential of obtaining a higher coverage ratio (Zhou, Bachmayer, & deYoung, ) because sonar dropouts at increased sonar angles can be compensated by conducting multiple revolutions at progressive depths as illustrated in Figure .…”

“…After that, the iceberg surface point can be processed using the sonar ranges and the iceberg‐related vehicle position. An iceberg edge‐following algorithm based on line‐of‐sight guidance law was developed for an AUV (Norgren & Skjetne, ). A multibeam sonar is oriented horizontally to measure the iceberg profile along the survey path.…”

A Real-Time Reaction Obstacle Avoidance Algorithm for Autonomous Underwater Vehicles in Unknown Environments

“…Norgren presented the obstacle avoidance method called “iceberg Edge-Following” in [ 24 ], however, the wall form of obstacles in this paper is too simple, and this obstacle avoidance method doesn’t adapt to complex U-shape obstacles, or labyrinth obstacles. The next question is when is the optimal time for ending this manner and driving straight to the target for complex wall form obstacles, which hasn’t been proposed in the above paper.…”

A Predictive Guidance Obstacle Avoidance Algorithm for AUV in Unknown Environments

“…The Montegrey, Calif. AUV Research Naval Postgraduate Institute conducted an experimental study on underwater reactive obstacle avoidance (OA) for AUVs, by mainly focusing on using the ARIES AUV and Blueview Blazed Array FLS for obstacle detection and avoidance [26]. In References [27,28], an improved line-of-sight (LOS) guidance algorithm is used for obstacle avoidance. At the same time, in the process of underwater obstacle avoidance, to achieve the optimal path obstacle avoidance [29,30], the path planning method was used.…”