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.
Highlights
The Precise Point Positioning (PPP) technique was introduced in the late nineties [1, 2] and uses state-space GNSS satellite orbit and clock bias solutions with significantly greater accuracy than their broadcast ephemeris counterparts in order to enable the user-segment to obtain accurate positioning with undifferenced data
Because some Small Unmanned Aerial Vehicle (SUAV) have very limited flight durations, which are on the order of fifteen minutes, or often less, some uncertainty remains as to whether PPP’s slow solution convergence will impact the accuracy of the postprocessed short duration SUAV solutions. To fill this knowledge gap, the contribution of this paper is to offer an experimental analysis of PPP techniques when compared to CP-Differential GPS (DGPS) with data collected onboard SUAV that has very short duration flights
Difference between Real-Time Kinematic (RTK) Global Positioning System (GPS) solutions Measured with a tape measure Mean RTK difference Figure 6: Phastball Zero SUAV GNSS antenna baseline separation as estimated by differencing the two RTK GPS solutions that are being used as reference solutions for PPP comparisons and by measuring with a tape measure
Summary
The Precise Point Positioning (PPP) technique was introduced in the late nineties [1, 2] and uses state-space GNSS satellite orbit and clock bias solutions with significantly greater accuracy than their broadcast ephemeris counterparts in order to enable the user-segment to obtain accurate positioning with undifferenced data. Zhang and Forsberg consider the use of PPP to support missions that require accuracy over very long-ranges (i.e., on the order of many hundreds of kilometers), thereby making doubledifferences to an individual reference station impractical [9]. In their assessment, Zhang and Forsberg use comparisons of airborne laser altimetry and satellite altimetry products to assess height solution accuracy from PPP and conclude that PPP can produce accuracy at the decimeter-level.
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