Radar Altimeter Characterization and Augmentation of Ground-Corrected Barometric Vertical Navigation of UAVs

Abstract

Urban air mobility (UAM) is a mobility and transportation concept that involves unmanned aerial vehicles (UAVs) flying at low altitudes in urban areas. In this context, knowing the precise altitude is crucial for flight safety. Vertical separations from other airspace participants, the ground, and other structures must always be ensured. Additionally, air taxis must be capable of performing safe and efficient vertical take-offs and landings (VTOLs) at designated vertiports in densely populated areas.

A key challenge for UAM is ensuring accurate, safe, and reliable navigation throughout all flight phases. This goal is typically achieved through global navigation satellite systems (GNSS). However, relying solely on GNSS presents several challenges regarding accuracy, availability, and security. The urban environment degrades the vertical accuracy and availability of GNSS-based solutions due to multipath effects, shadowing of satellite signals, and poor sky visibility. Moreover, there is a considerable security risk from signal interference due to jamming and spoofing, for which simple countermeasures do not exist.

In this thesis, a GNSS-independent sensor-fusion approach is developed and investigated in response to these issues. The proposed system provides accurate altitude information for altitude control during VTOL operations at vertiports. For this purpose, an airborne short-range radar altimeter and an airborne barometer are employed together with a vertiport ground station providing assistance. In assisting air vehicles around the vertiport, the ground station broadcasts the ground temperature and pressure measurements concurrently with the terrain altitude and position of the associated vertiport. As these data also need to be processed and fused, an outline for that is presented, and a Kalman-based extended filter is developed.

The filter is then tested using test flight data collected during the HorizonUAM project of the German Aerospace Center (DLR) and simulation data for the radar. The results are encouraging and promising concerning the accuracy and potential performance of the presented approach, but they also highlight the need for future work.