We propose a novel technique for guidance of buoyancy-controlled vehicles in uncertain under-ice ocean flows. In-situ melt rate measurements collected at the grounding zone of Antarctic ice shelves, where the ice shelf meets the underlying bedrock, are essential to constrain models of future sea level rise. Buoyancy-controlled vehicles, which control their vertical position in the water column through internal actuation but have no means of horizontal propulsion, offer an affordable and reliable platform for such in-situ data collection. However, reaching the grounding zone requires vehicles to traverse tens of kilometers under the ice shelf, with approximate position knowledge and no means of communication, in highly variable and uncertain ocean currents. To address this challenge, we propose a partially observable MDP approach that exploits model-based knowledge of the under-ice currents and, critically, of their uncertainty, to synthesize effective guidance policies. The approach uses approximate dynamic programming to model uncertainty in the currents, and QMDP to address localization uncertainty. Numerical experiments show that the policy can deliver up to 88.8% of underwater vehicles to the grounding zone -- a 33% improvement compared to state-of-the-art guidance techniques, and a 262% improvement over uncontrolled drifters. Collectively, these results show that model-based under-ice guidance is a highly promising technique for exploration of under-ice cavities, and has the potential to enable cost-effective and scalable access to these challenging and rarely observed environments.

翻译：我们提出了一种新颖的技术，用于在不确定的冰下洋流中导引浮力控制航行器。在南极冰架接地带（即冰架与下伏基岩相接的区域）采集的原位融化速率测量数据，对于约束未来海平面上升模型至关重要。浮力控制航行器通过内部驱动控制其在水柱中的垂直位置，但缺乏水平推进手段，为此类原位数据采集提供了一种经济可靠的平台。然而，到达接地带需要航行器在冰架下穿越数十公里，其间仅有近似位置信息且无法通信，并面临高度多变和不确定的洋流。为应对这一挑战，我们提出了一种部分可观测马尔可夫决策过程方法，该方法利用基于模型的冰下洋流知识，特别是其不确定性知识，来合成有效的导引策略。该方法使用近似动态规划来建模洋流的不确定性，并使用QMDP来处理定位不确定性。数值实验表明，该策略可将高达88.8%的水下航行器送达接地带——相比最先进的导引技术提升了33%，相较于无控漂流器则提升了262%。总体而言，这些结果表明，基于模型的冰下导引是一种极具前景的冰下空腔探索技术，并有望实现对这些极具挑战性且罕有观测的环境进行经济高效且可扩展的探测。