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Application of the undifferenced GNSS precise positioning in determining coordinates in national reference frames

Krzan Grzegorz, Stępniak Katarzyna

Artificial Satellites : Journal of Planetary Geodesy

2017

Vol. 52, No. 3

49--69

In high-accuracy positioning using GNSS, the most common solution is still relative positioning using double-difference observations of dual-frequency measurements. An increasingly popular alternative to relative positioning are undifferenced approaches, which are designed to make full use of modern satellite systems and signals. Positions referenced to global International Terrestrial Reference Frame (ITRF2008) obtained from Precise Point Positioning (PPP) or Undifferenced (UD) network solutions have to be transformed to national (regional) reference frame, which introduces additional bases related to the transformation process. In this paper, satellite observations from two test networks using different observation time series were processed. The first test concerns the positioning accuracy from processing one year of dual-frequency GPS observations from 14 EUREF Permanent Network (EPN) stations using NAPEOS 3.3.1 software. The results were transformed into a national reference frame (PL-ETRF2000) and compared to positions from an EPN cumulative solution, which was adopted as the true coordinates. Daily observations were processed using PPP and UD multi-station solutions to determine the final accuracy resulting from satellite positioning, the transformation to national coordinate systems and Eurasian intraplate plate velocities. The second numerical test involved similar processing strategies of post-processing carried out using different observation time series (30 min., 1 hour, 2 hours, daily) and different classes of GNSS receivers. The centimeter accuracy of results presented in the national coordinate system satisfies the requirements of many surveying and engineering applications.

The problem of temporal validity of reference coordinates in the context of reliability of the ETRS89 system realization in Poland

Szafranek K.

Artificial Satellites : Journal of Planetary Geodesy

2012

Vol. 47, No. 4

177--188

The IAG (International Association of Geodesy) Sub-Commission for the European reference frame (EUREF) passed a resolution recommending application of the ETRF2000 frame as national realizations of the ETRS89 reference system during the XXth EUREF Symposium in Gävle (Sweden) in 2010. The PL-ETRF2000 system is comprised of EPN (EUREF Permanent Network) sites. Their coordinates and their temporal changes (velocities) were accurately determined on the basis of long-term GNSS observations. The transfer of the PLETRF2000 system onto the territory of Poland is realized by the ASG-EUPOS (Active Geodetic Network – European Position Determination System) permanent sites network. The ASG-EUPOS tasks include also system maintenance by continuous or periodical control of the coordinates and velocities constancy. According to the current Regulation of the Ministry of Administration and Digitization concerning geodesic, gravimetric and magnetic warps, the accuracy of sites of the fundamental warp (EPN sites belonging to ASG-EUPOS) may not be worse than 0.01 m for horizontal position and 0.02 m for geodesic height. It results in the necessity to monitor the performance of the reference sites for proper maintenance of the reference system. A new team for modeling deformations in Europe was established within the EUREF Working Group (The EUREF Working Group on Deformation Models) during the EUREF 2012 Symposium in Paris. One of its tasks is taking geo-kinematic models into consideration for national realizations of the ETRS89 and maximum usage of knowledge concerning the velocity field. The paper deals with the problem of temporal validity of the catalogue coordinates and the necessity of periodical updating them on the basis of velocities derived from long-term observations. Although Poland is located in a tectonically calm area and the intraplate velocities are small, some of the EPN and ASG-EUPOS sites have significant velocities and are subject to vertical movements. Lack of periodical updating of the coordinates realizing the reference system will cause lack of fulfillment of the assumed accuracy criterion. Analysis of horizontal and vertical velocities of sites belonging to the fundamental warp lead to assumption that two sites will exceed horizontal criterion in a period of time shorter than 10 years counting from the reference epoch (i.e. from 2011.0): KATO horizontal coordinates should be updated in 2014 and GWWL in 2021. Mores sites will exceed vertical criterion: BOGI (2021), GWWL (2015), KATO (2019), SWKI (2019) and ZYWI (2021). The vertical component updating will require of course changes of the horizontal component (coordinates are determined in the Cartesian orthogonal XYZ coordinate system and then recalculated for the ellipsoidal coordinates). Besides periodical coordinates updating it is recommended to conduct repeated processing for the entire network according to the EUREF standards for taking the current GNSS observations into consideration.