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Investigation of Using Sky Openness Ratio as Predictor for Navigation Performance in Urban-like Environment to
Chao Deng1, Chung-Hung John Wang1, Kin Huat Low2
1Air Traffic Management Research Institute, Nanyang Technological University, Singapore 637460, Singapore.
Sensors (Basel, Switzerland)
|February 15, 2022
Summary
Navigation errors in Unmanned Aircraft Systems (UAS) are worsened by urban environments. The study found GPS uncertainty estimates and sky openness do not reliably predict horizontal position errors during UAS flights near buildings.
Area of Science:
- Aerospace Engineering
- Robotics
- Geomatics Engineering
Background:
- Navigation accuracy is critical for Unmanned Aircraft Systems (UAS).
- Urban environments introduce significant challenges, particularly multipath interference, affecting UAS positioning.
- Understanding the impact of urban obstructions on UAS navigation is vital for safe operations.
Purpose of the Study:
- To investigate how different urban operational environments influence the lateral (horizontal) navigation performance of a self-built UAS.
- To analyze the relationship between Global Positioning System (GPS) reported uncertainty, satellite visibility, sky openness, and actual horizontal position error.
- To assess the suitability of current GPS metrics for monitoring UAS navigation performance in complex urban settings.
Main Methods:
- Conducted real flight tests with a self-built UAS in diverse urban environments (open areas, obstructed paths, building corners, reflective surfaces).
- Collected GPS position data and compared it against Real-Time Kinematics (RTK) derived ground truth to determine horizontal position error.
- Analyzed data considering GPS horizontal position uncertainty estimate (EPH), number of visible satellites, and sky openness ratio (SOR).
Main Results:
- No direct correlation was found between the GPS receiver's reported horizontal position uncertainty estimate (EPH) and the measured horizontal position error.
- The EPH is not a reliable indicator for monitoring UAS navigation performance in urban environments.
- A universal correlation between sky openness ratio (SOR) and horizontal position error was not observed, indicating environmental complexity.
Conclusions:
- Current GPS uncertainty estimates are insufficient for real-time navigation performance monitoring of UAS in urban areas.
- Predicting UAS horizontal navigation uncertainty requires more sophisticated models that account for complex 3D urban geometry and signal propagation.
- Further research is needed to develop robust methods for assessing and managing UAS navigation safety within the Urban Air Mobility (UAM) and UAS Traffic Management (UTM) frameworks.
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