Reliability Analysis of a Quasi-Instantaneous Ambiguity Fixing Method

Telmo Cunha, Phillip Tome, Sergio Cunha and Luisa Bastos

Abstract:	This paper describes a method for L1 ambiguity determination that requires only a few seconds of data (typically 3 to 10), for DGPS kinematic applications. This methodology is based on dual frequency data and is suitable for situations where the data rate is relatively high (1 Hz or higher), which is typical for most kinematic surveys. The proposed methodology takes into consideration the fact that some parameters are better estimated at a higher sampling frequency. Based on this and a few other strategies described in this paper, a reduced ambiguity search space is generated. The selection of the best candidate takes into account, among other factors, the residuals of both L1 and L2 carrier phase measurements, making use of the correlation that exists between them regarding the unique antenna position, and the wide-lane ambiguity. This set of algorithms was implemented as a user-friendly computer application, which is able to process data both in real-time and post-processing mode. This paper demonstrates the reliability of this method by presenting results obtained from several tests, under different conditions, and with sufficient trials to withdraw statistical conclusions about its performance. The ionospheric influence is also analyzed together with the behavior of the method with increasing baseline length. The issue of employing multiple reference stations is also addressed, with test data analysis indicating a performance improvement of the method over larger areas. Almost instantaneous high-precision positioning can benefit many surveying applications. Achieving a subdecimeter precision with only a few seconds of observation improves the productivity of any land survey, like, for example, photogrametric point surveying or kinematic surveys where the obstruction of satellite signals can occur quite frequently. When operating in real-time, the developed software allows the user to view graphically the quality of the estimated position on-line. For short-static applications, this feature enables the user to survey a point only during the strictly necessary time and not for a predefined, and usually over-determined, interval.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	1540 - 1549
Cite this article:	Cunha, Telmo, Tome, Phillip, Cunha, Sergio, Bastos, Luisa, "Reliability Analysis of a Quasi-Instantaneous Ambiguity Fixing Method," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 1540-1549.
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