Many EPN stations provide GNSS data in real-time. Disseminating their streams via NTRIP became an EPN routine operation. The aim of this Special Project is the processing of these data to derive and disseminate new real-time GNSS products while gaining experience with the real-time analysis in general.
Objectives of the Special Project are:
- Processing and analysis of real-time GNSS data for:
- the extension or modification of existing EPN products
- the development of new EPN products in order to improve positioning in Europe (regional products)
- Stable dissemination of real-time GNSS data and products with an elaborated backup system
More details about the concept and goals can be found here.
Increasing the GNSS Stream Dissemination Capacity (concept; last updated: July 16, 2009).
Satellite Clock and Orbit Corrections
A minimum service for the real-time PPP support is provided via estimating real-time precise satellite clock and orbit corrections with respect to the navigation messages. As satellite clock and orbit determination needs access to global resources, this Special Project cooperates with and contributes to the Real-time IGS (RTIGS) Pilot Project which is dedicated to the same subject.
The first approach which consists in producing real-time clock and orbit correctors to Broadcast Ephemeris of GPS and GLONASS satellites is described in detail in the clocks and orbits computation section.
Precise Point Positioning
Within the Precise Point Positioning (PPP) approach only observations from a single rover receiver are used. Since error sources are not eliminated in the PPP, which is based on undifferenced observations, they must be properly modeled or corrected. The most important and at the same time minimum corrections are provided through real-time precise orbits and clocks using so-called "State Space Representation" (SSR) approach (Schmitz, 2012, Wübbena, 2012). Details of the potential of modern PPP algorithms can be found in, e.g., Wübbena et al., 2005 and Mervart et al., 2008.
The goal of this part of the work is to evaluate the PPP accuracy reachable in real-time: A sole EUREF and IGS based service shall allow real-time decimeter-level satellite positioning everywhere on the European continent when using a dual frequency GNSS receiver.
Incoming real-time GNSS observations from the EPN network as well as derived clocks and orbits are continuously monitored. Monitor results describing completeness and latency of observations are derived in the context of converting RTCM streams to 1sec/15min RINEX files.
Except for the scientific community, real-time GNSS products like satellite clocks and orbits remain of marginal value unless they come in a standardized format supported by receiver firmware. The Special Project therefore supports the standardization under development in the State Space Working Group of RTCM SC-104. The tools used so far for clock and orbit correction processing and dissemination (see here) follow RTCM Recommended Standards and proposals documented in RTCM working papers. Encoding/decoding routines used in this Special Project will be updated when new RTCM proposals become available.
Estimating satellite clocks and orbits from EUREF and IGS sources is understood as a first and minimum step in real-time GNSS support for user-end PPP applications. Deriving other real-time products mainly focused on ionosphere and troposphere products or hardware bias estimation in order to support PPP regional ambiguity resolution and finally aimed for regional augmentations with instantaneous ambiguity resolution on user-side (i.e., PPP-RTK providing an alternative to RTK) should be main objective for future developments within European real-time activities.
There is an increasing interest in real-time developments and applications making a static list of project members difficult. However, colleagues of various organizations are supporting this Special Project, namely Federal Agency for Cartography and Geodesy (BKG), Germany (W. Söhne (chair), A. Stürze, G. Weber), Royal Observatory (ROB) Belgium (C. Bruyninx), Czech Technical University Prague (CTU), Department of Geodesy (Z. Lukes, L. Mervart), Geodetic Observatory Pecny (GOP), Czech Republic (J. Dousa), German Aerospace Center (DLR), Germany (A. Hauschild, O. Montenbruck), Geo++ GmbH, Germany (M. Schmitz, G. Wübbena), Alberding GmbH, Germany (D. Stöcker), and others.
- Mervart L., Z. Lukes, C. Rocken, T. Iwabuchi, 2008, Precise Point Positioning With Ambiguity Resolution in Real-Time, ION GNSS 2008
- Weber G., L. Mervart, Z. Lukes, C. Rocken, J. Dousa, 2007, Real-time Clock and Orbit Corrections for Improved Point Positioning via NTRIP, ION GNSS 2007
- Wübbena G., M. Schmitz, A. Bagge, 2005, PPP-RTK: Precise Point Positioning Using State-Space Representation in RTK Networks, ION GNSS 2005
- Schmitz M., 2012, RTCM State Space Representation Messages, Status and Plans, PPP-RTK Symposium, Frankfurt am Main, 2012
- Söhne W., 2010, EPN Special Project "Real-time Analysis" - Status Report, EUREF Symposium, Gevle, 2010
- Wübbena G., 2012, RTCM State Space Representation (SSR), Overall Concept Towards PPP-RTK, PPP-RTK Symposium, Frankfurt am Main, 2012
[email protected] for questions related to product generation and dissemination,
[email protected] for questions related to GNSS data monitoring.