Using the virtual reference stations (VRS) concept for long-range airborne GPS kinematic positioning

In this paper, the potential of long-range kinematic GPS positioning with a multiple reference station (MRS) network for airborne applications is discussed. A novel method of creating Virtual Reference Stations (VRS) is proposed for post-processed airborne GPS kinematic applications, which is called the modified semi-kinematic VRS method (MS-VRS). The purpose of the VRS is to generate data from real GPS observations made by the MRS network, resembling that of a non-existing (virtual) reference station situated close to the project area, so that the commonly used methods for short-range kinematic GPS data processing can be used to determine the position of the aircraft. During the initial phase, the VRS of the MS-VRS method refers to a fixed position according to the aircraft's initial approximate position, and the corrections are applied according to the aircraft's trajectory. The MS-VRS method differs from the conventional VRS method and semi-kinematic VRS method (S-VRS) in that when the aircraft's current approximate position is more than 10 km from the initial VRS position, a new VRS is created. The MS-VRS data can be generated in RINEX format, so that it can be processed using any kinematic GPS post-processing software. Using a simulated kinematic test with static data, the MS-VRS method showed a 12.1 to 47.6 percent improvement in the three coordinate components with respect to the conventional single reference station (SRS) approach. Tests and analysis with real airborne GPS data are presented in some detail using a MRS network and flight test data in Norway. The results indicate that centimetre-level accuracy can be achieved based on the proposed MS-VRS method, which is superior to the S-VRS method, with improvements of 11.4 to 47.4 percent in terms of standard deviations of the coordinate domain

First Results from Virtual Reference Station (VRS) and Precise Point Positioning (PPP) GPS Research at the Western Australian Centre for Geodesy

Over the past 18 months, a team in the Western Australian Centre for Geodesy at Curtin University of Technology, Perth, has been researching the optimum configurations to achieve long-range and precise GPS-based aircraft positioning for subsequent airborne mapping projects. Three parallel strategies have been adopted to solve this problem: virtual reference stations (VRS), precise point positioning (PPP), and multiple reference stations (MRS). This paper briefly summarises the concepts behind the PPP and VRS techniques, describes the development and testing of in-house software, and presents the latest experimental results of our research. Current comparisons of the PPP and VRS techniques with an independently well-controlled aircraft trajectory and ground-based stations in Norway show that each deliver precisions of around 3 cm. However, the implementation of more sophisticated error modelling strategies in the MRS approach is expected to better deliver our project’s objectives

An Approach for Instantaneous Ambiguity Resolution for Medium- to Long-range Multiple Reference Station Networks

Integer ambiguity resolution (AR) is a prerequisite for all high-precision (centimetre level) GPS applications that utilise multiple reference station (MRS) networks. However, due to the presence of distance-dependent GPS errors, notably atmospheric refraction, AR across the network is difficult on an epoch-by-epoch basis, especially for medium- to long-range (typically 30?130 km as used here) MRS networks. This paper presents an approach for medium- to long-range instantaneous AR for MRS networks, based on an ionosphere-weighted observation model and network geometry constraints, along with a multiple ambiguity validation test procedure. The performance of the proposed method was demonstrated through two case-study examples from Australia and Norway. Our test results show that the instantaneous AR success rate varied from 93% (131 km baseline) to 98% (35 km baseline).It is also shown that the adopted high-precision prediction models for the double-difference (DD) ionospheric delay and residual tropospheric zenith delay (RTZD) are of benefit to the high success rate of the network AR. Due to its epoch-by-epoch nature, the proposed approach is insensitive to cycle-slips, rising or setting satellites, or loss-of-lock