Improved Sensing Strategies for Low Altitude Non Cooperative Sense and Avoid

Very low altitude non-cooperative sense and avoid is considered as an essential component of multi-layered mitigation strategies for collision hazard within the UTM/U-Space framework. However, it currently represents a challenging problem with open issues concerning performance trade-offs and technological options. In fact, low altitude operations emphasize sensing challenges such as ground clutter removal for radar, and below-the-horizon detection for optical sensors. These issues have a significant impact in scenarios involving small UAS, which may be characterized by low detectability though potentially generating relatively fast encounter geometries. As a contribution to this framework, this paper proposes some improved sensing strategies for these scenarios. The first idea is to optimize architectural and algorithmic trade-offs by accounting for the possible closure rates corresponding to near collision scenarios. This approach can be used to develop adaptive sensing strategies, as well as to select different sensors to cover different areas of the aircraft field of regard. The concept is demonstrated in numerical analyses focused on the computation of probability of missed and false conflict detection. Then, with regards to purely visual architectures, the possibility to extract and use shape-based ranging information to improve conflict detection performance is investigated through flight tests with small UAS. Finally, the paper describes first experimental activities conducted with a compact collision avoidance radar.