From Mark.Caissy at NRCan-RNCan.gc.ca Fri Apr 3 02:12:29 2009 From: Mark.Caissy at NRCan-RNCan.gc.ca (Caissy, Mark) Date: Fri, 3 Apr 2009 05:12:29 -0400 Subject: [IGSMAIL-5927]: Status of IGS Real Time Pilot Project Message-ID: <159FD28F03D76E468EE6650EB50072D008656600@S0-OTT-X2.nrn.nrcan.gc.ca> ****************************************************************************** IGS Electronic Mail 03 Apr 02:12:32 PDT 2009 Message Number 5927 ****************************************************************************** Author: Mark Caissy Status of IGS Real Time Pilot Project Dear IGS colleagues, We have compiled this message to update everyone on the activities that are taking place under the scope of the Real Time Pilot Project. We hope that this will encourage increased participation to the project as well as highlighting the good work that is taking place. Objectives ------------- The following outline the key objectives of the Pilot Project: 1. Manage and maintain a global IGS real-time GNSS tracking network. 2. Enhance and improve selected IGS products. 3. Generate real-time products. 4. Investigate standards and formats for real-time data collection, data dissemination and delivery of derived products. 5. Monitor the integrity of IGU predicted orbits and GNSS status. 6. Distribute real-time observations and derived products to real-time users. 7. Support Network DGPS/RTK 8. Encourage cooperation among real-time activities, particularly in IGS densification areas. Data Products ----------------- There are two systems in operation for delivery of Real Time data streams to RTPP contributors. UDPRelay is operated by NRCan and delivers data from approximately 50 stations to authorised users, using standardised data formats and the UDP protocol. An archiver application (RTIGSA) can decode the streams and create binary files that can be converted to RINEX using the TEQC application. An RT-IGS Multicast Receive Software (RTIGSMR) receives the RTIGS data stream and provides users with a framework to develop applications. Further information is available at http://www.rtigs.net/architecture.php. In the BKG NTRIP infrastructure, the data sources (receivers) transmit their data to the broadcast servers using the NtripServer application. A number of NtripCasters serve data to users in different communities using the HTTP protocol. The IGS Caster www.igs-ip.net serves as the RTIGS-NTRIP Interface for the IGS Pilot Project. It disseminates data for nearly 150 stations, mainly in RTCM3 and RTIGS formats. A small number of stations transmit in various flavours of RTCM2. Ntrip server and Ntrip client software for various operating systems is available under GPL. Further information can be found at http://igs.bkg.bund.de/index_ntrip.htm. Analysis Products ---------------------- A number of contributing Real Time Analysis Centres provide daily clock RINEX and SP3 product files to ESOC, which performs the AC coordination activities. The products are derived from the Real Time infrastructure of the individual Analysis Centres. ESOC then computes a combination clock product which is disseminated daily, along with a comparison summary report. The algorithms used for the combination are the same as will be used in the near future for providing a Real Time combination product stream. This will comprise the clock corrections for the GPS satellites and the IGU-predicted orbits. The daily combination clock RINEX files and comparison reports are now uploaded to the CDDIS data server and can be found under ftp://cddis.nasa.gov/gps/products/rtpp/. Target combination product performances are: Satellite Clock Accuracy: 0.3 ns Station Clock Accuracy: 0.3 ns Orbit Accuracy: At the level of the IGS Ultra predictions Latency (when available in RT): 10 s The clock accuracy is measured as the RMS difference between the IGS rapid or final clock solution and the combination solution, after removing a common offset per epoch. Analysis Centres -------------------- A brief description of the Analysis Centres that are currently contributing their solutions and their software infrastructure is given below: ESOC: The software system at ESOC is called RETINA (System for Real Time Navigation) and it integrates core infrastructure elements for RT processing (Job Scheduling and Monitoring, Graphics, History Files allowing for streaming and retrieving historical data seamlessly, network monitoring) with Real Time and Batch applications. Orbits are generated using similar processes to the ultra-rapids at configurable intervals (currently every 2 hours). A Real Time filter estimates spacecraft clocks, receiver clocks, tropospheric zenith delays and phase ambiguities. Automated comparisons are performed between batch and RT products and with IGS Finals. The ESOC solution stream currently uses data from the RTIGS server at NRCan. A second solution, ESOC2, is running in parallel, using data from the NTRIP casters and including measurements from approximately 40 stations. This makes use of the IGS Ultra-Rapids for orbit information. Processing frequency is variable and 1-second processing is possible but currently ESOC is using a 5-second frequency to maximise the online data span. Clock comparisons with IGS are at the 0.2-0.45 ns level RMS, depending on network availability. NRCan: A least-squares batch process computes orbits every hour for the IGS Ultra-Rapid product. The predicted portions of these orbits are held fixed in a real-time sequential least-squares filter to estimate the satellite clocks, receiver clocks, station tropospheric zenith delays and phase ambiguities every two seconds. Orbit and clock corrections referenced to the Broadcast ephemerides are disseminated in a modified-RTCA (MRTCA) format with 4mm precision. Computing infrastructure includes development, test and production servers. Correction validation is performed in real-time and hourly. Combined product accuracy (User Range Error, URE) is at the 10 - 15 cm level. A real-time ionospheric product is generated over a regional (North-American) coverage area and provided for single-frequency users. BKG with TU Prague: The RTNet package is used in the context of the Pilot Project to estimate clock biases, tropospheric zenith delays and phase ambiguities every second. It currently uses orbits from the IGS Ultra-Rapids. RTNet processing includes data from GPS and GLONASS. The clock corrections are designed to correct the double difference observable but absolute clock corrections will be provided in the future for comparison/combination purposes. The accuracy is sub-decimetre over Europe and is available within 5-7 minutes after filter initialisation. Two additional software applications have been developed for peripheral tasks: (i) BNC, a GPL tool for feeding real-time GNSS engines with streams coming in SOC, RTCMv2 or RTCMv3 format, converting streams to RINEXv2 or v3 observation and navigation files and monitoring real-time GNSS networks (ii) BNS, a tool for encoding clock and orbit corrections to RTCMv3 and streaming to Ntrip broadcasters. DLR: The RETICLE software estimates Real Time spacecraft clock biases and drifts, receiver clock biases, tropospheric zenith delays and phase ambiguities, using a Kalman filter. The software uses the IGS Ultras as a source of orbit information. GMV: The software is a GMV's own development, based on software developed for Galileo for orbit determination and time synchronisation. It has been tested with Near Real Time GPS and Giove data. It currently produces products every hour. The SW is under improvement to increase the frequency of outputs and to eventually include a Real Time data acquisition and processing capability. A number of additional centres are in the process of developing their systems and expect to be able to contribute their solutions in the near future. They include GFZ, Geo++, IGG, Chalmers, University of Newcastle, TU Catalonia and KASI. Formats and Protocols --------------------------- Formats including RTCM 3.0, BINEX and RTCA are being investigated as part of the PP activities. The objective is the development of an open standard that will meet the needs of a future IGS Real-time Service. This objective is being pursued during the pilot project through the work of the Real Time Working Group. In our efforts to develop standards and protocols for Real Time data and product dissemination, we have found synergies with the RTCM community (see www.rtcm.org). The IGS has applied for membership to the RTCM and is actively participating in SC104, the Special Committee dealing with Differential Global Navigation Satellite Systems (DGNSS). The advantage of working through the RTCM is that the resulting formats will be adopted by the receiver manufacturers, allowing seamless integration of data and products between tracking receivers, data and analysis centres and users in the field. Users ------- A number of proposals from users of the RTPP data and products have been received. Until the Real Time products become available, users whose objective is to evaluate the potential accuracies achievable are invited to start downloading and processing the combination product in the form of daily clock RINEX files from ftp://cddis.nasa.gov/gps/products/rtpp/. Loukis Agrotis (RT Analysis Centre Coordinator) Mark Caissy (RTWG Chair)