Map-based Height Above Ground Estimation for Safe Operation Monitoring of Unmanned Aircraft in Very Low Level Airspaces

Abstract

According to current European regulations, most common drone operations are limited to a maximum altitude of 120m above ground. However, a direct measurement of the height above ground is usually not available for small drones. Consequently, ensuring compliance to height above ground constraints may prove to be difficult for many scenarios, especially when flying over complex terrain or beyond the visual line-of-sight of a remote pilot. In this work, we investigate the use of a satellite-based navigation and digital terrain maps to estimate the height above ground. We propose to integrate this estimation into a runtime assurance architecture with a safe operation monitor ensuring compliance to the maximum height above ground imposed by regulatory or operational constraints. We assess the feasibility and limitations of the approach, by analyzing sources of errors including navigation uncertainty and elevation data accuracy. We present the design and implementation details of a height above ground estimation and monitoring system and show results from flight tests with a multicopter drone. The presented results indicate the practicability and current limitations of a map-based height above ground estimation for drones operated in very low level airspaces.