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By Sunil Bisnath and Dave Wells RTK Workshop 26-28 August 2002 Stennis Space Center

GPS Activities at the Hydrographic Science Research Center, Department of Marine Science, The University of Southern Mississippi. By Sunil Bisnath and Dave Wells RTK Workshop 26-28 August 2002 Stennis Space Center. OUTLINE. Formation of the GPS research thrust GPS research activities

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By Sunil Bisnath and Dave Wells RTK Workshop 26-28 August 2002 Stennis Space Center

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  1. GPS Activities at theHydrographic Science Research Center,Department of Marine Science,The University of Southern Mississippi By Sunil Bisnath and Dave Wells RTK Workshop 26-28 August 2002 Stennis Space Center

  2. OUTLINE • Formation of the GPS research thrust • GPS research activities • Current projects • 2001 NGLI buoy analysis • C-NAV receiver solution analysis • Future plans • Near-term support for NAVOCEANO • Long-term proposed projects

  3. FORMATION OF THE GPS RESEARCH THRUST • Rationale: • Positioning and navigation, principally by GPS, a cornerstone of hydrographic activities • Purpose: • Designed to support positioning and navigation needs of NAVOCEANO • Personnel: • David Wells • Sunil Bisnath • Dave Dodd • Erik Quiroz

  4. GPS RESEARCH ACTIVITIES • Testing and evaluation: • GPS receiver hardware and software • GPS processing software • Operational procedures and training: • Development of these items • Practical knowledge transfer • Forward-looking: • Technological developments • Technology-driven changes to procedures

  5. 2001 NGLI BUOY ANALYSIS • Experiment description: • Buoy equipped with an RTK GPS receiver and other sensors placed off the coast of Mississippi in summer of 2001 • Purpose: • Observe effectiveness of determining water levels from GPS on such a platform • Equipment and methodology: • ~ 10 km baseline • NovAtel OEM4 receivers • Other sensors used, including three accelerometers • NovAtel RTK solution recorded at buoy receiver • Analysis: • HSRC tasked with analysis of RTK solutions

  6. RTK SOLUTION AVAILABILITY: 7 SEPT. 2001 Float Fixed

  7. RTK SOLUTION AVAILABILITY: 8 SEPT. 2001

  8. RTK SOLUTION AVAILABILITY: 9 SEPT. 2001

  9. RTK SOLUTION AVAILABILITY: SEPT. 2001 Mean

  10. DISCUSSION: DATA AND SOLUTION GAPS • Solution availability statistics: • Mean = 81% • Std. dev. = 18 % • ~ 50 % of days have < 90 % availability • Probably causes: • Daily recording gaps due to CPU housekeeping • Buoy-related restrictions (e.g., power, GPS receiver, etc.) • Communications link-related restrictions • Available data: • Good satellite coverage and available RTK solutions for periods with GPS solutions

  11. RTK SOLUTION RESULTS: 22 SEPT. 2001

  12. RTK SOLUTION RESULTS: 23 SEPT. 2001

  13. RTK HEIGHT SOLUTION RESULTS: 23 SEPT. 2001 Incorrect ambiguity Filter artifacts

  14. RTK HEIGHT SOLUTION RESULTS: 23 SEPT. 2001 Incorrect ambiguity Filter artifacts

  15. DISCUSSION: HEIGHT SOLUTION ARTIFACTSAND POSSIBLE CAUSES • Very short re-initialization period after data gaps • Appears to be a processing filter-based error being introduced in solution • Incorrectly determined ambiguities are apparent in solution (infrequent, but may last several tens of minutes)

  16. RTK HEIGHT VERSUS ACCELEROMETER:15 SEPT. 2001 GPS Accel.

  17. RTK HEIGHT SOLUTION PRECISION: 23 SEPT. 2001

  18. ACCURACY ASSESSMENT OF MARINE (KINEMATIC) GPS DATA • Solution precision estimates from receiver are mostly likely internal precision values based on mathematical and stochastic models used • Precision estimates do not always represent the quality of the solution • Observed artifacts such as filtering effects and mis-identified ambiguities are not represented in precision estimates • How to determine the accuracy of marine (kinematic) GPS solutions in practice?

  19. IMPROVEMENTS FOR 2002 EXPERIMENT • Increase solution availability rates by correcting for buoy system restrictions • Remove filter-based artifacts by altering processing inputs • Collocate buoy with tide gauges to allow for accuracy assessment of GPS-determined heights • Save all raw data for varied post-processing runs • Study alternative methods of providing precision estimates for RTK solutions

  20. C-NAV SOLUTION ANALYSIS • C-NAV system: • Developed by C&C Technologies, Inc., based on C&C and NavCom hardware and NavCom and JPL software • Not a baseline-dependent RTK solution, but rather point position solution utilizing precise satellite ephemerides and clock offsets provided by real-time satellite link • Receiver algorithms still in the development stage • Analysis: • HSRC tasked with evaluating performance present generation of system

  21. C-NAV RTG SOLUTION AVAILABILITY: 20 AUG. 2002

  22. C-NAV RTG SOLUTION AVAILABILITY: 21 AUG. 2002

  23. C-NAV RTG SOLUTION AVAILABILITY: 22 AUG. 2002

  24. C-NAV RTG HEIGHT SOLUTION RESULTS:20-22 AUG. 2002

  25. C-NAV RTG HEIGHT SOLUTION RESULTS:20-22 AUG. 2002

  26. C-NAV RTG HEIGHT SOLUTION RESULTS:20-22 AUG. 2002 (All values in centimeters)

  27. COLD-START C-NAV HEIGHT SOLUTION CONVERGENCE: 19,22,23 AUG. 2002 ~ solution convergence

  28. POTENTIAL OF C-NAV USAGE • Great potential of system: • No baseline restrictions • No base station infrastructure requirements • Uniform global coverage • Desirable improvements: • Accuracy • Repeatability • Quantified system integrity • Shorten solution convergence period for practical use in situations where signal block is an issue

  29. HSRC NEAR-TERM SUPPORT FOR NAVOCEANO • Continued NovAtel (RTK) evaluation • Continued C-NAV (precise point positioning) evaluation • 2002 buoy RTK solution evaluation and raw GPS data processing

  30. HSRC LONG-TERM PROPOSED RESEARCH • Establishment of high-precision, kinematic GPS test facility at Stennis • Study extension of RTK baselines, specifically effect of differential troposphere • Study alternative methods of providing precision estimates for RTK solutions • Investigate effects of GPS modernization and Galileo on hydrographic surveying results and therefore procedures • Investigate augmentation of GNSS technology with other sensors • Develop GPS training materials

  31. ACKNOWLEDGEMENTS • NAVOCEANO for providing data, processing, and feedback on our analysis • PSI for providing technical information for the buoy data processing • C&C Technologies, Inc. for providing a C-NAV receiver and technical support • Department of Marine Science personnel for providing feedback on our analysis

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