A preliminary study on UAS vertical NSE analysis in urban-like environments

Abstract

UAS navigational error is one of the concerns leading to non-conformance of assigned flight volume. This is especially noticeable in urban environment where global navigation satellite system (GNSS) positioning capability are affected by influencing factors such as signal blockage and multipath errors caused by surrounding objects like buildings, trees, and other obstructions [1]. This paper presents a study on how the vertical navigation performance is affected by the cause of change in the sky openness ratio (i.e., GNSS signal blockage) above the drone when a self-built UAS is operating near several types of urban obstructions in flight tests. Test sites are carefully selected to ensure they are representative to urban environments, which includes 1) open space carpark with a few short trees, 2) running parallel to row of buildings, 3) surrounded by buildings (narrow urban canyon), and 4) constraint area with a building and some tall trees. The data will be analysed to obtain the vertical position error with considerations for (i) Number of visible satellites versus flight altitude, (ii) Sensor-reported vertical co-variance (EPV), (iii) Vertical position errors at various locations by comparing the reported position (GNSS) to a reference value, and (iv) Factors contributing to vertical positional errors at various locations, (v) The influence of sky openness to the vertical position error. The measurement of sky-openness ratio is to determine whether 3D city model of the flight area is sufficient to predict the vertical navigation performance that could be expected.