Quality Assessment of GNSS Simulations for Flight Procedures based on Onboard Recorded Flight Data

Implementation of new satellite based flight procedures in Switzerland are always accompanied by simulations in order to assess the positioning solution performance and the resulting availability. This approach is even more important when procedures are designed in mountainous environment such as the Swiss Alps, where terrain masking of more than 20 degrees may be present. 30th International Technical Meeting of the Satellite Division of the Institute of Navigation (ION GNSS+ 2017), Portland, Oregon, September 25-29, 2017 1633 These simulations cover the desired flight path or relevant points in space where the most critical terrain masking is expected. An in-house software tool was developed to perform these studies. A Digital Elevation Model (DEM) and the designed flight path is loaded into the tool. In a first step, the horizon along the desired flight path is calculated. In cases, where the terrain elevation exceeds 10 degrees over a relevant azimuthal sector, a more in-depth assessment is required. In these cases, Global Positioning System (GPS) almanacs at different epochs are loaded and simulations covering a period of a sidereal day are carried out. Availability of satellite signals are finally derived from these calculations. In this study, data recorded onboard of helicopters is used to compare real performance with simulated ones. Different areas of influence are analyzed including the required DEM resolution and sampling rate, signal masking caused by the helicopter and flight attitude. The findings lead to a qualitative classification of the input parameters for the simulation tool. The classes describe the severity of the impact on the simulation results. This helps to optimally choose input parameters to achieve high quality simulation results.