Multi-Observable Processing Techniques for Precise Relative Positioning

M. Timo Allison

Abstract:	Relative positioning applications which exploit the accuracy of the GPS dual-frequency carrier phase observables continue to expand as new receiver technologies become available. Although techniques designed to utilize the maximum information content of the GPS signals have been discussed for many years, in practice their use has been limited. This has been primarily due to the unavailability of low cost receivers in the survey market which offer full GPS signal observability on the Ll and L2 frequencies. With the advent of new advanced receiver technologies, this situation is rapidly changing. Traditionally, high precision relative positioning and geodetic surveying utilized only Ll and L2 carrier phase measurements. These are inherently ambiguous, and classical techniques designed to resolve the integer lane ambiguities impose constraints on the relative motion of the receivers. Multi-observable processing, which utilizes pseudorange in addition to carrier phase, removes the necessity for receivers to remain relatively static at any time, and eliminates special initialization procedures. As a direct consequence, numerous kinematic applications become feasible. These include photogrammetry, hydrographic surveying, and real-time applications such as precision approach landing of aircraft. Static surveying is also enhanced by reducing the satellite observation time. Multi-observable processing options are compared in the light of current and emerging dual-frequency GPS receiver technology. Ironically, as P-code receivers finally become affordable to the survey community, there is an increasing fear that DoD policy will result in encryption of the P-code into the classified Y-code (Anti-Spoofing or AS) on all Block II satellites within the next couple of years. The impact on multi-observable processing is discussed. Static survey results are presented using 3-observable processing with observation times of 1 and 5 minutes.
Published in:	Proceedings of the 4th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1991) September 11 - 13, 1991 Albuquerque, NM
Pages:	715 - 726
Cite this article:	Allison, M. Timo, "Multi-Observable Processing Techniques for Precise Relative Positioning," Proceedings of the 4th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1991), Albuquerque, NM, September 1991, pp. 715-726.
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