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Active SLAM using 3D Submap Saliency for Underwater Volumetric Exploration

In this paper, we present an active SLAM framework for volumetric exploration of 3D underwater environments with multibeam sonar. Recent work in integrated SLAM and planning performs localization while maintaining volumetric free-space information. However, an absence of informative loop closures can lead to imperfect maps, and therefore unsafe behavior. To solve this, we propose a navigation policy that reduces vehicle pose uncertainty by balancing between volumetric exploration and revisitation. To identify locations to revisit, we build a 3D visual dictionary from real-world sonar data and compute a metric of submap saliency. Revisit actions are chosen based on propagated pose uncertainty and sensor information gain. Loop closures are integrated as constraints in our pose-graph SLAM formulation and these deform the global occupancy grid map. We evaluate our performance in simulation and real-world experiments, and highlight the advantages over an uncertainty-agnostic framework.