Undifferenced Ionosphere and Troposphere Estimation for Network Kinematic GPS

P.M. Grgich

Abstract:	Network Kinematic GPS enables almost instantaneous positioning at centimetre level accuracy. However, the use of Network Kinematic GPS techniques is currently limited to a range of some tens of kilometres from the Continuously Operating Reference Stations (CORS). This limited range is caused by the difficulty in estimating the ionospheric and tropospheric biases at the rover position that is in turn largely caused by the difficulty in estimating the atmospheric delays at the CORS sites. This research develops algorithms that enable the estimation of ionospheric and tropospheric delays using undifferenced code and carrier phase observations while ensuring rigorous ambiguity estimation. The undifferenced methodology is proposed as it is more rigorous than double differencing and makes optimal use of all information contained in the measurements. The method of estimating the atmospheric delays presented here consists of four steps: floating point ambiguity estimation, ambiguity fixing, satellite clock error estimation and the final pass that generates the atmospheric delays. The algorithms described in this paper utilise segmented least squares adjustments to estimate the floating point undifferenced phase ambiguities in a feasible timeframe, while still using all observations. Once these floating point ambiguities have been estimated, the ambiguity fixing is undertaken. Further segmentation of the solution is then conducted to solve for residual satellite clock errors. Finally, once these errors are solved for and removed, the ionospheric and tropospheric delays are estimated on an epoch by epoch and station by station basis. Based on the results presented here, this estimation process is capable of yielding delays that are accurate to the millimetre level. This in turn will enable more accurate interpolation of ionospheric and tropospheric delays at the rover position for use in Network Kinematic GPS. The outcomes of the improved ability to estimate atmospheric delays will be that the distance from the CORS sites that Network Kinematic GPS can be performed will be greater, the accuracy and reliability of Network Kinematic GPS positions will improve and that rover end ambiguity resolution will be quicker and more reliable.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	651 - 660
Cite this article:	Grgich, P.M., "Undifferenced Ionosphere and Troposphere Estimation for Network Kinematic GPS," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 651-660.
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