Optical aircraft navigation with multi-sensor SLAM and infinite depth features

In the context of optical-aided navigation and visual Simultaneous Localization And Mapping (SLAM) for satellite-denied aircraft navigation, this paper extends the monocular SLAM approach by the use of multiple sensors with different viewing directions. Downward optical sensors see other movements than forward-looking cameras, hence it is straightforward to combine the benefits of both. This combination helps to estimate all the six motion components with increased robustness, yielding a more stable and accurate state estimation for optical-aided navigation solutions. The method is evaluated with aerial data from manned and unmanned flights. In the data analysis, a satellite navigation dropout is simulated, and the flight trajectory is then reconstructed just by the optical data. The method is tested in small-scale scenarios as well as in longer flights with several kilometers of flight range. The results show some increased performance of an additional forward camera in comparison to a setup with only downward sensors. It is proposed to use such multi-sensor configurations wherever motion estimation ambiguities with a single camera are probable, especially when larger distances have to be flown with optical navigation.