Terrain Maps for Low Altitude Aviation from Commercial Satellite Photogrammetry

Safe low-altitude flight operations necessitate accurate terrain mapping capabilities to mitigate multiple operational hazards. This report evaluates an emerging mapping methodology, satellite image photogrammetric mapping, and its applicability to flight safety requirements. Aerial lidar surveys have historically represented the primary methodology for generating detailed three-dimensional terrain maps. These systems provide exceptional spatial resolution capabilities, typically achieving decimeter-level accuracy that exceeds the meter-level requirements necessary for spatial hazard identification. However, widespread adoption of mapping from aerial lidar surveys is limited by high acquisition costs and data volume management challenges. Recent developments in commercial satellite imaging have enabled alternative mapping approaches utilizing stereo matching and photogrammetric processing techniques. Compared to maps based on aerial lidar surveys, maps based satellite imagery are less expensive, faster to prepare, easier to distribute, and scalable to wider areas. This report asks two questions. First, do maps based on satellite imagery possess the spatial resolution and accuracy required for flight hazard reduction? Second, are maps based on satellite imagery consistent over time, i.e., do they correctly track changes as the landscape changes? This report, based on evaluation of a series of four satellite-based maps of a 100 km2 area acquired at six month intervals over 2 years, concludes that they do meet the required levels of resolution and accuracy needed to identify most, but not all, terrain hazards. For undetected terrain hazards (thin features such as power lines), one approach to supplementing satellite-based maps is described. Further, consistency checks over time found that the 3D features were stable in static regions of the landscape and were reliably updated in regions of the landscape that changed.