Multi-Modal Loop Closing in Unstructured Planetary Environments with Visually Enriched Submaps - Giubilato, Riccardo; Vayugundla, Mallikarjuna; Stürzl, Wolfgang; Schuster, Martin; Wedler, Armin; Triebel, Rudolph (2021 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2021)