C-Nav GPS System & the Seamless Vertical Datum

1. C-Nav GPS System & the Seamless Vertical Datum GPS Services Group C&C Technologies, Inc., (Lafayette, La) www.cctechnol.com

2. Real Time Gipsy (RTG) • Current release provides sub-meter level horizontal accuracies. • Version 12.2 (beta) test indicates decimeter level horizontal accuracy. • We will be discussing Version 12.2

3. The C-Nav RTG Methodology • Does not use the ‘traditional’ (RTCM) measurement domain or position domain correction methods, nor is it RTK. • Corrects each source of error. • Broadcasts correctors for orbits and satellite clocks. • Dual-frequency code and carrier phase measurement are used to form pseudoranges free from ionospheric delays.

4. Real Time Gipsy (RTG) • ‘Worldwide’ Global GPS Network (GGN) reference stations transmit all of their RAW GPS dual frequency observations to three Network Processing Hub locations (SF & JPL) via TCP/IP and the ‘Internet’. • The NPH’s performs the task of breaking down the GPS range error sources into their component, User Independent, parts in real-time. • Independent Refraction Corrected Orbit and Atomic Clock Offset corrections (to the broadcast ephemeris) for all GPS satellites are computed (by the NPH), and transmitted via Land Earth Stations for uplink over StarFire L-Band communication satellites. • The user requires a Dual-Frequency GPS receiver to be used at their remote location so that computation of the ‘local’Refraction Corrected pseudorange observations can be obtained. • The GPS receiver applies the received RTG Orbit and Clock corrections along with the internally computed, Refraction Corrected, GPS Satellite pseudorange observations to compute a 3D surface position.

5. StarFire Global Network

6. Brewster, USA Cordoba, Argentina Christiansted,Virgin Islands Fairbanks, USA Galapagos Island, Ecuador Greenbelt, USA Goldstone, USA Dededo, Guam Krugersdorp, South Africa Bangalore, India JPL Pasadena, USA Kokee Park, USA Robledo, Spain Ross Island, Antarctica Mauna Kea, USA Moscow, Russia Franceville, Gabon Norilsk, Russia Lamont, USA Quezon City, Phillipines Bishkek, Kryghystan Santiago, Chile Tidbinbilla, Australia USNO, USA Usuda, Japan Yakutsk, Russia RTG Reference Sites Global Network (26+)

7. C-Nav GPS User System Basic System Hardware ‘Bundle’: • 1 x C-Nav GPS Receiver • 1 x C-Nav Control Display Unit (CnC D.U.) • 1 x C-Nav GPS Receiver Data and Power Y-Cable • 1 x DC Power Cable • 1 x Power Supply • 1 x C-Nav Operations Manual • 1 x Software Utilities

8. C-Nav GPS Receiver Design • Multi-function L-Band antenna • 12 channel dual-frequency, geodetic grade GPS engine • L-Band communications receiver and embedded microprocessor • Patented multi-path reduction signal processing capability and P code recovery algorithm • Dual-frequency code and carrier phase measurement are used to form smooth refraction corrected code pseudoranges • Compact size and integrated package design

9. C-Nav Features • ‘Global corrected’ GPS Positioning ( RTG, WCT & WAAS ) • 1Hz NMEA Msgs ( GGA, GLL, GSA, GST, RMC, VTG, ZDA ) • Proprietary NMEA Data Msgs ( SATS, NAVQ, RXQ, NETQ ) • RTCM Output ( Standard RTCM Type 1 PRC – every 5 seconds ) • Dual Frequency, Geodetic GPS Engine to resolve local Ionospheric delay observation errors • Multipath Mitigation Algorithm • Rugged and waterproof Single Integrated Package • Low Power Consumption ( < 10 Watts – 9v to 40v d.c.) • 5Hz positioning and data output ( w/o CnC Display Unit ) • Automatic Restart based on last operating configuration

10. C&C (C-Nav) Locations

11. Vertical Accuracy • IHO SP 57, 1987 • 0.3 meters at 90% confidence • Assuming Gaussian: • 0.36 meters at 95% confidence

12. Vertical Accuracy • IHO S 57, 1998, category 1: • Depth error of 0.5 m at 95% confidence. • Assume sounding error of 0.36 meters at 95%: • Allowable “Tide” 0.35 meters at 95% confidence.

13. Vertical Accuracy • IHO S 57, 1998, category “special”: • Depth error of 0.25 m at 95% confidence. • Assume sounding error of 0.15 meters at 95%: • Allowable “Tide” 0.20 meters at 95% confidence.

14. Vertical Accuracy • NOS Specifications and Deliverables • January 2002: • Tidal errors range from 0.2 m to 0.45 m • at 95% confidence.

15. Vertical Accuracy • A vertical accuracy of 0.35 meters at 95% confidence is sufficient for all IHO categories except “special” and is about as accurate as a tide-based datum. • A vertical accuracy of 0.2 meters at 95% confidence is sufficient for IHO “Special” surveys and is about as good as the best tide based datum.

16.   Figure 1: SD = 0.386 m Figure 2: SD 0.277 Figure 3: SD = 0.197 m

17. High Multipath

19. Good Data 95% of data is within 0.41 meters of the mean. Max HDOP = 3, max speed = 6 m/s; Discard stand alone GPS.

20. Good Data

21. How Good? • Vertical accuracy of about 0.41 meters at 95%. • About the same as NOS zoned tides in the most difficult areas. • Can be used for IHO Category 1, but sounding errors must be limited to 0.3 meter at 95%. • Further testing needed to confirm accuracy and understand restrictions.

22. Conclusions • Vertical accuracy of about 0.41 meters • Multipath needs to be controlled. • About ten minutes to sub-meter data. • About 2 hours to decimeter data.