Predicting and correcting scale induced biases resulting from the application of regional orbit and clock corrections

© Springer International Publishing Switzerland 2015. Real-time orbit and clock corrections to GPS broadcast ephemeris, in short broadcast corrections (BCs), have become available as International GNSS Service (IGS) products through the IGS Real-time Service (RTS) in 2013. The BCs are distributed via the Network Transport of RTCMby Internet Protocol (NTRIP) according to RTCMState Space Representation standards. When applying the BCs in real-time Precise Point Positioning (PPP), user positions with sub-decimetre precision after convergence can be obtained. The IGS BCs refer to the International Terrestrial Reference Frame 2008 (ITRF2008). BCs in regional reference frames (RBCs) are available through regional NTRIP broadcasters in Europe, North-America, South-America and Australia. The IGS RTS website states that: Applying orbit and clock corrections from regional product streams in a real-time PPP solution automatically leads to regional coordinates. The PPP client would not need to transform coordinates because that is already done on the server side. However, in contrast to the PPP-approach that uses BCs in ITRF2008 followed by a transformation to the local datum, the approach based on RBCs causes a bias in the PPP solution due to the scale factor between regional and global reference frames. This scale induced bias is satellite geometry dependent when the conventional 14-parameter transformation from the global to the regional reference frame is applied to the satellite position vectors in ITRF2008, to derive the RBCs from the IGS BCs. The size of the scale induced bias is significant. The bias is up to 8 cm for the Australian GDA94 and up to 0.5 cm for the North American NAD83. Currently an additional satellite position dependent value is added to the satellite clock correction to deal with the scale induced biases of three RBCs, resulting in a transformed clock correction (Weber, BKG Ntrip Client (BNC) Version 2.9 – Manual, 2013). Applying these transformed clocks results in a remaining scale induced bias of less then 10mm for each RBC of ETRF2000, NAD83 and SIRGAS2000. For GDA94 the remaining scale induced bias is maximum 30 mm, this is caused by the large scale factor of GDA94 compared to other regional reference frames. This contribution will show that the remaining bias in the PPP solution is practically independent from satellite geometry and depends mainly on the user position; hence the remaining bias can be predicted and corrected for at any location

Assessment of rst Real-Time IGS global VTEC maps

The assessment of the first Real-Time (RT) IGS global VTEC maps computed by DLR and UPC, against JASON-1 (during 2011) and JASON-2 altimeter VTEC measurements (2012), is presented in this work. Indeed, within the International GNSS Service (IGS), Associate Analysis Centres (ACC) produce specialized or derived products. Two examples of Real-time ACCs are the Universitat Politecnica de Catalunya (UPC) and the German Aerospace Center (DLR). They have participated in the IGS Real Time Pilot Project (RTPP) and continue to collaborate on the development of a combined global IGS RT-VTEC product. This collaboration is occurring under the umbrella of the IGS Ionosphere Working group (IGS Iono-WG) currently lead by the University of Warmia and Mazury in Olsztyn, Poland. RT-VTEC information is used to support earth observation missions and space weather monitoring and forecast. RT-VTEC information can improve single-frequency positioning on a global scale and in smaller regions where the ionosphere may be well sounded. RT-VTEC information is known to improve RTPPP accuracy results for single-frequency users. Through the use of iono-geodetic techniques, phase quality dual-frequency RTPPP results are being improved by reducing the convergence time for phase ambiguity fixing. The JASON comparisons are considered pessimistic for the overall global VTEC product accuracy because the land-based tracking stations are generally located quite far from the location of the JASON measurements. The importance of a reliable globally distributed and su�ciently dense real-time GNSS tracking network will be shown. Moreover the RT-VTEC results are quite compatible with the rapid and final IGS VTEC maps for a significant fraction of time. These results suggest that it may be feasible to combine real-time VTEC products from several centres into a robust IGS real- time IONO product. Additional work to compare both solutions is underway with the goal of �nding optimal ways to assess and combine these products into an IGS RT- VTEC product. Future efforts will include working with RTCM to ensure that the IGS RT-VTEC product is compatible with ionosphere correction information proposed for the RTCM-SSR standar

Simulation case study of deformations and landslides using real-time GNSS precise point positioning technique

[EN] The precise point positioning (PPP) is a Global Navigation Satellite System (GNSS) computation technique that performs precise positioning using a single receiver. This is the main advantage over the traditional differential positioning for geodesy and geomatics which requires, at least, two receivers to get a precise position or a single receiver connected to a network of reference stations. The main goal of this work was to study the real-time PPP technique for deformation and landslides monitoring. A custom designed device was used for the simulation of landslides, and several test campaigns were performed at field. A control unit was designed based on open-source software and Python libraries implemented in this research. The conclusion of the study shows that realtime PPP allows solutions for deformation monitoring with mean offsets of 2 cm in north, east and up components, and standard deviations of 2 cm. It demonstrates the reliability of real-time PPP monitoring systems to detect deformations up to 5 cm of magnitude when the double constellation (GPSCGLONASS) was used. Finally, an improvement in the results with the recovery of fixed ambiguities in the PPP algorithms is outlined.Capilla Roma, R.; Berné Valero, JL.; Martín Furones, ÁE.; Rodrigo Alemany, R. (2016). Simulation case study of deformations and landslides using real-time GNSS precise point positioning technique. Geomatics, Natural Hazards and Risk. 7(6):1856-1873. doi:10.1080/19475705.2015.1137243S185618737