GNSS Geodetic Reference Frames: Consistency, Stability and the Related Transformation Parameters

Mojtaba Bahrami and Marek Ziebart

Abstract:	In this paper, relationships between GNSS terrestrial reference frames are investigated and the related frame transformation parameters are given. These transformation estimates enable multi-GNSS users to obtain positioning solutions within a particular reference frame of choice and correct any reference frame discrepancies. For high-accuracy multi-constellation GNSS positioning and navigation these transformations should be taken into account otherwise the gains from multi-constellation solutions could be impaired. This also helps separate reference frame effects from other sources of error. The relationship between reference frames and their stability/instability and consistency is assessed by estimating the similarity (Helmert) transformation parameters (origin, scale and orientation) of one frame with respect to an external secular stable reference frame and the frame parameters time-evolutions are studied in this paper. Moreover, the Root Mean Square (RMS) is used as a statistical estimator to qualify the repeatability or precision of the time-series of the Helmert parameters of the corresponding frames. The study focuses on the current GNSS systems, the GPS and the GLONASS system. GPS WGS-84 and GLONASS PZ-90.02 reference frames are assessed with respect to the International GNSS Service (IGS) IGS05 reference frame and the related frame transformation parameters are determined at the orbital altitude using long-term time-series of satellite positions (i.e. broadcast/- precise ephemerides) in respective frames. Our analyses show that the GPS WGS-84 reference frame has maintained consistency with the IGS05 which is completely equivalent to the International Terrestrial Reference Frame (ITRF) in orientation, translation and scale. The magnitudes of the estimated frame transformation parameters indicate that these two reference frames are essentially identical with differences being statistically insignificant for most applications. Comparisons between the National Geospatial-Intelligence Agency (NGA) GPS precise ephemerides, referenced to WGS-84, and IGS GPS precise final ephemerides, referenced to IGS05, after the adjustment of a best fitting Helmert transformation show a RMS difference of few centimeters per component of the satellite positions (with total magnitude RMS error of <= 20 cm). The difference is most likely due to different orbit determination/prediction models used by the NGA and the IGS analysis centers. The long-term time series of the transformation parameters between the GLONASS PZ-90.02 and IGS05 reference frames indicated that (since September 2007) the PZ-90.02 and IGS05 which conforms to the ITRF reference frames are in agreement on the order of a few decimeter. Comparisons between the broadcast GLONASS PZ-90.02 and precise IGS05 reference frames, after the adjustment of a best fitting Helmert transformation, show their agreement on the order of < 4 m with accuracies limited by the quality of the broadcast PZ-90.02 ephemerides.
Published in:	Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011) September 20 - 23, 2011 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	2318 - 2331
Cite this article:	Bahrami, Mojtaba, Ziebart, Marek, "GNSS Geodetic Reference Frames: Consistency, Stability and the Related Transformation Parameters," Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011), Portland, OR, September 2011, pp. 2318-2331.
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