Toward the Ultimate RTK: The Last Challenges in Long-Range Real-Time Kinematic Applications

Don Kim, Richard B. Langley

Abstract:	Although significant improvements in handling the unmodelled atmospheric (i.e., ionospheric and tropospheric) delays for long-range RTK (real-time kinematic) applications have been made by many research groups over the world, it is often found that the residual tropospheric delay is still the most problematic error source for such applications. One of the most challenging issues with respect to the residual tropospheric delay is that the two coefficients associated with the tropospheric zenith delay and the up component of a positioning solution (i.e., the tropospheric mapping functions and the up components of the design matrix) are almost linearly correlated above a 20 degree elevation angle. In this case, variations in the tropospheric zenith delay are almost indistinguishable from those in the up component at high elevation angles. In the conventional approaches, satellites being observed at low elevation angles can help the least-squares estimator break up the correlation associated with two parameters. If no satellite is available at low elevation angles, an adaptive estimator of the tropospheric zenith delay can relieve the problem to some degree. In this paper, we propose a new approach to overcome the challenges associated with the residual tropospheric delay. The tropospheric zenith delay and the up component of a positioning solution combine into a single parameter to remove the ill-conditioned problem induced by the correlation of two parameters. This new parameterization coincides with a weighting process of the tropospheric mapping functions and the up components of the design matrix using a scale factor. The main features of the new approach are highlighted, including compatibility, controllability, singularity and redundancy.
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	385 - 396
Cite this article:	Kim, Don, Langley, Richard B., "Toward the Ultimate RTK: The Last Challenges in Long-Range Real-Time Kinematic Applications," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 385-396.
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