Flight-Test Evaluation of Kinematic Precise Point Positioning of Small UAVs

Abstract

An experimental analysis of Global Positioning System (GPS) flight data collected onboard a Small Unmanned Aerial Vehicle (SUAV) is conducted in order to demonstrate that postprocessed kinematic Precise Point Positioning (PPP) solutions with precisions approximately 6 cm 3D Residual Sum of Squares (RSOS) can be obtained on SUAVs that have short duration flights with limited observational periods (i.e., only ~≤5 minutes of data). This is a significant result for the UAV flight testing community because an important and relevant benefit of the PPP technique over traditional Differential GPS (DGPS) techniques, such as Real-Time Kinematic (RTK), is that there is no requirement for maintaining a short baseline separation to a differential GNSS reference station. Because SUAVs are an attractive platform for applications such as aerial surveying, precision agriculture, and remote sensing, this paper offers an experimental evaluation of kinematic PPP estimation strategies using SUAV platform data. In particular, an analysis is presented in which the position solutions that are obtained from postprocessing recorded UAV flight data with various PPP software and strategies are compared to solutions that were obtained using traditional double-differenced ambiguity fixed carrier-phase Differential GPS (CP-DGPS). This offers valuable insight to assist designers of SUAV navigation systems whose applications require precise positioning.

GPS precise point positioning for UAV photogrammetry

“…The centimetre‐level precision of the agreement between GPS PPP and PPK trajectories in all coordinates, as presented in Table , is commensurate with the results of Gross et al. (). The mean differences are about 1 to 3 cm in plan and about 10 cm in height, which are substantial improvements over the Gross et al.…”

“…This indicates the sensitivity of GPS PPP solutions to instantaneous satellite geometry distributions, suggesting that low satellite elevation cut-off angles should be used during PPP processing when possible. The centimetrelevel precision of the agreement between GPS PPP and PPK trajectories in all coordinates, as presented in Table III, is commensurate with the results of Gross et al (2016). The mean differences are about 1 to 3 cm in plan and about 10 cm in height, which are substantial improvements over the Gross et al (2016) mean error differences of 60 to 80 cm, which is attributed to the longer flight durations of 25 to 29 minutes used here, enabling the ambiguities to be estimated more accurately, rather than in their 3-to 5-minute flight durations.…”

“…This substantially improves on the metre‐level accuracies previously reported by Gross et al. (), which is attributed to arise from the longer data spans from the longer flight durations, enabling the more accurate estimation of the GPS ambiguity parameters. It is also shown that solutions are sensitive to the satellite elevation cut‐off angle, whilst it is expected that height errors are also introduced by antenna phase centre variations that could not be modelled (although these also applied to the relative PPK solutions), as well as residual tropospheric delay effects.…”

“…While the GPS PPP errors are substantially smaller than those found from the UAV experiments of Gross et al. (), further work is needed to reduce the outstanding bias of about 10 cm in height if GCPs are to be completely eliminated. Apart from having a sufficiently long flight duration to accurately estimate the ambiguity parameters, other factors affecting the height component, in particular, include antenna phase centre variation modelling, the optimum mitigation of the tropospheric delay, time‐of‐day geometry effects (plus the impact of observations from other GNSS constellations such as GLONASS) and resolving the ambiguities to integers.…”

“…The increased UAV platform dynamics over land-based vehicles also makes accurate GPS positioning more challenging. Gross et al (2016) undertook kinematic PPP on three UAV missions, but with flight durations in the range of 2Á6 to 5Á7 minutes. These resulted in reported UAV positioning accuracies in the range of 0Á61 to 1Á39 m, albeit with centimetre-level precision.…”