hydro8 Precise Point Positioning, the new DGPS: The C-Nav Experience Edwin Danson FRICS FInstCES FRAS Business strategy consultant

Transcription

1 hydro8 Precise Point Positioning, the new DGPS: The C-Nav Experience Edwin Danson FRICS FInstCES FRAS Business strategy consultant

2 C-Nav Worldwide Precise Point Positioning with In-built Autonomy for Assurance of Quality, Accuracy, Integrity and Real-time Monitoring OBJECTIVES Consider the drivers for commercial GNSS augmentation vendors Familiarisation with C-Nav as a PPP solution Consider the reliability and redundancy issues Accuracy and precision The commercial products and support services Look at some of the applications for PPP accuracy

3 Commercial drivers The commercial marine market dependent on accurate position: Surveying Vessel and platform positioning Position-dependent marine activities ca. 2,4Bn DP Construction control and management Scientific instrumentation platforms Pipe and cable lays and recovery Mining and mineral extractors Environmental studies Conservancy and port works Coastal zone management etc

4 Commercial drivers Managing the positioning risks: An accurate and reliable position is critical for all offshore activities... There are no compromises as far as positioning is concerned someone has to be accountable Networks Robust communications with redundancy Overdetermined solutions (redundancy in tracking stations) Multiple LES uplinks with redundant solutions Redundancy in processing centres Quality control Dual systems On-line QC F-test, w-test, MDE, etc

5 Commercial drivers Managing the positioning risks: An accurate and reliable position is critical for all offshore activities... There are no compromises as far as positioning is concerned someone has to be accountable Security Dual systems, dual delivery Independent systems Accountability Contractual terms Company audits Fiscal control Management and project control Legal recourse

6 C-Nav GcGNSS The C-Nav global GcGNSS network delivers a dynamic position anywhere in the world with accuracy typically <10cm. Uses a Globally Corrected (GcGNSS) state-space solution (Precise Point Positioning) No dependence on local reference stations or post-processing Precise Point Positioning derived in proprietary version of JPL s Real-time GIPSY solution Broadcasts satellite orbit and clock corrections for all GNSS satellites simultaneously Same accuracy virtually anywhere on the Earth s surface from 72ºN to 72º S latitude Simple and easy to install hardware

7 C-Nav Overview Global GNSS Tracking Network Six Uplinks Six highpower Inmarsat SVs VSAT Internet ISDN Links Global corrections broadcast to user community Raw L1/L2 data and observables Two Hot Hubs Illinois, USA California, USA JPL (Back Up) 40,000 + users Worldwide

8 Network Tracking Stations Global network of 70+ C-Nav tracking stations C-Nav tracking stations are equipped with duplicate: Geodetic quality, dual-frequency GPS receivers (A & B receivers) Processors Communication interfaces Multiple communications links Reference receivers decode GNSS signals, and send precise high-quality dual-frequency observables and carrier phase measurements to the processing centers Data links use the Internet as the primary data link, backed up by dedicated communication lines Network is sufficiently dense that the tracking stations effectively act as backups to each other

9 Processing Centres All raw data sent to two Processing Centers Located geographically distant from each other and running continuously o Torrance, Western USA o Moline, Central USA Computes PPP corrections for each satellite in the constellation using proprietary RTG software Each Processing Center computes: Real Time Orbit Corrections every Minute Resolution <1cm Real Time Clock Corrections every few Seconds Resolution <1cm US Naval Observatory used as Master Clock with (five alternate atomic standards as backup)

10 C-Nav Modeled Errors Geopotential Solid tide (dynamic) Solid tide (kinematic) Pole tide Ocean tide Ocean loading Atmospheric loading Point mass attraction for the planets and Sun Phase windup Satellite yaw Earth albedo and IR Solar pressure Relativity (kinematic) Relativity (dynamic) Troposphere Empirical parameters to model residual acceleration effects

11 Uplinks From the two Processing Centers, the four sets of corrections are sent to six Land Earth Stations (LES) for uplink to six L-band communications satellites. Redundant communication links to the LESs (frame relay, ISDN, Internet) Redundant live equipment at each LES Each L-Band satellite covers more than a third of the Earth, providing global coverage between 72º North to 72 South Net-1 LES sites Perth, Australia Laurentides, Canada Burum, Netherlands Satellites 98W (Americas) 25E (Europe) 109E (Asia/Pacific) Net-2 LES sites Auckland, New Zealand Santa Paula, California Southbury, Connecticut Satellites 142W (Americas / Pacific) 15.5W (Americas / Europe) 143.5E (Asia /Pacific)

12 Redundancy The C-Nav Network utilizes two different geographically separated processing centers to compute corrections for Net-1 and Net-2 Each processing center has totally redundant hardware, data links, and runs independent software The Net-1 and Net-2 signals are broadcast by different satellites each uploaded from different Land Earth Stations (LES) Each region of the world is covered by two independent satellites Each uplink site has redundant Internet connections

13 Redundancy (Net-1 & Net-2)

14 Redundancy Shipboard equipment: GNSS receivers can be licensed to operate using either Net-1, Net-2 correction signals or use both Networks for maximum reliability. Vessels can be equipped with two separate position systems that both provide the global accuracy C-Nav users have come to expect. There is no change in positional accuracy when switching between C-Nav Net-1 and Net-2 decimeter services.

15 Performance -C-Nav PPP

16 Cold-start - De Beers Marine Performance -C-Nav PPP

17 C-Nav QC 1994, UKOOA - Use of DGPS in Offshore Positioning - The document remains a standard familiar to all who work offshore C-Nav QC - proprietary Receiver Autonomous Integrity Monitoring (RAIM) algorithm to detect, identify and eliminate outliers, and report the rejection process via NMEA messages The RAIM algorithm differs from that of the UKOOA guide being more sensitive, using techniques not available in 1994 After eliminating outliers, C-Nav QC performs statistical analysis on remaining observations, reporting these per the IMO/NMEA and UKOOA guidelines

18 C-Nav QC Outlier detection and elimination based on a w-statistic for each observation using a proprietary technique more sensitive at detecting outliers than the former sequential w-test. Type II errors are detected and reported per IMO requirements for RAIM and correlate with the UKOOA statistic Marginally Detectable Error (MDE) directly equivalent to the UKOOA method Unit variance, F-test of unit variance, and horizontal error ellipse (95%) are calculated per the UKOOA guidelines

19 Water level measurements C-Nav demonstrated as a vertical reference system for tide measurement in 2003 by the University of Southern Mississippi in 2004 the University of New Brunswick 4.3cm SD vertical component detected the tides to a level commensurate with IHO Special Order surveys In 2004 NAVOCEANO can no longer rely on the traditional methods for conducting hydrographic surveys... uses C-Nav RTG technology and GPS buoys (to) provide a capability to obtain hydrographic information anywhere outside territorial waters... Correction for tide only has meaning where the tidal variation exceeds IHO boundary limits, i.e. <500 metres

20 Water level measurements Any system that measures water level variations is, by definition, a tide gauge All that is needed is knowledge of the correlation between the instantaneous vertical at the place of observation and the vertical at one or more tide gauges. A number of countries are already advanced in determining these offsets: US, majority of primary gauges are in ITRF framework UK, Vertical Offshore Reference Frame (VORF) Modelling through EGM96 / MSL does not meet directly IHO standards

21 Improving the error budget Precision and accuracy at the decimetre level allows removal of much of the noise in the classic error budget. Swath bathymetry Horizontal accuracy leads to better resolution of seabed features Vertical accuracy improves the spatial resolution of soundings I.e. the primary error sources are reduced to those of acoustic transmissions and inherent instrumental precision

22 Passing on the benefits High order real-time surface positioning leads to an improvement in subsea positions reliant on a surfacebased datum e.g. for ROVs, UUV and AUVs. For Dynamic Positioning systems, high accuracy avoids the problems of stability Better position management = reduced fuel consumption. For example, a DP construction vessel equipped with dynamic PPP can save 400 litres of fuel per day

23 Passing on the benefits Seismic acquisition The ability to integrate a complex acquisition matrix in a highly constrained network has advantages for reducing surface and semi-surface position uncertainties and improving 3/4D seismic imagery. Seismic companies have focused on this for the last 15 years In 1992, WGS SARGAS / Wimpol ORION LRRTK was achieving dynamic ~25cm at 1,200km Today s dynamic PPP solutions deliver ~10cm across the globe... and for considerably less cost

24 RTK augmentation RTK Extend Overcomes the problem of RTK failure when comms with the base station are lost RTK Extend provides centimetre accuracy for up to 15 minutes during communication loss allows users to work without interruptions seamlessly switching between the modes Firmware option for all C-Nav dual frequency receivers RTK correctors

25 RTK augmentation RTK ULTRA Overcomes the problem of RTK decorrelating range limitations RTK ULTRA RTK precision has been demonstrated beyond 70 kilometres from base station allows users to work over areas 400% greater than is possible with conventional RTK RTK ULTRA is available with all C-Nav dual frequency receivers

26 Conclusions C-Nav is an example of industry working with academia to embrace the next generation of precision GNSS augmentation ~10 cm dynamic horizontal accuracy is now the norm, not the exception ~15 cm vertical accuracy opens the way for real-time IHO standard water level correctors PPP stability and precision effectively removes position error from the Error Budget Integrating RTK with PPP augmentation delivers very high accuracy over large areas and reduces lost time through comms outages

27 Thank you C-Nav Division C&C Technologies, Inc 730 East Kaliste Saloom Road Lafayette, Louisiana, USA