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Sunil Bisnath and David Dodd Hydrographic Science Research Center,

INITIAL RESULTS FROM AN ANALYSIS OF TROPOSPHERIC CORRECTIONS ON NDGPS. Sunil Bisnath and David Dodd Hydrographic Science Research Center, Department of Marine Science, University of Southern Mississippi USCG C2CEN Meeting 15-17 June, Portsmouth, Virginia. OVERVIEW OF PRESENTATION.

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Sunil Bisnath and David Dodd Hydrographic Science Research Center,

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  1. INITIAL RESULTS FROM AN ANALYSIS OF TROPOSPHERIC CORRECTIONS ON NDGPS Sunil Bisnath and David Dodd Hydrographic Science Research Center, Department of Marine Science, University of Southern Mississippi USCG C2CEN Meeting 15-17 June, Portsmouth, Virginia

  2. OVERVIEW OF PRESENTATION • Project introduction • Evaluation methodology • Initial results • Conclusions and future work

  3. INTRODUCTION

  4. PROJECT INTRODUCTION • Background: • For NDGPS to meet higher accuracy demands, tropospheric delay modeling (along with other error handling) must be significantly improved • NOAA has developed a conventional / GPS tropospheric model • Objectives: • An independent, extensive analysis of NOAA model • Analysis of improvement in GPS data processing results • Analysis of how data can be delivered and applied

  5. hydrostatic or “dry” delay wet delay ~ 90% of total delay / e.g., 180 cm / mostly predictable ~ 10% of total delay / e.g., 20 cm / very irregular TROPOSPHERIC REFRACTION IN GPS tropo delay =  (atmospheric pressure, temperature) +  (water vapor pressure, temperature)

  6. k k mf1k*zpd1k j j mf1k*zpd1k mf2k*zpd2k mf2k*zpd2k mf1j*zpd1j mf1j*zpd1j mf2j*zpd2j mf2j*zpd2j 1 2 1 2 “short” baseline “long” baseline Double-difference slant delay = (mf1j * zpd1j - mf1k * zpd1k) - (mf2j * zpd2j - mf2k * zpd2k) zpd1j ~ zpd2j ; zpd1k ~ zpd2k mf1j ~ mf2j ; mf1k ~ mf2k  slant delay ~ 0 SPATIOTEMPORAL DECORRELATION troposphere

  7. EVALUATION METHODOLOGY

  8. METHODOLOGY • First phase of analysis: range domain evaluations • Compare NOAA tropo. corrections against other predictors in space and time

  9. MODELS / ESTIMATES:IGS SINEX PRODUCT • GPS-only estimate of ZPD at fixed sites • Blended solution from number of int’l organizations • Estimated precision: < 1 cm reference solution

  10. MODELS / ESTIMATES:NOAA TROPOSPHERIC PRODUCT • Developed by Forecast Systems Lab, NOAA • http://www.gpsmet.noaa.gov • Numerical weather prediction model output using GPS data assimilated from CONUS • Input: lat., long., ell. hgt., time • Output: zenith hydrostatic delay and zenith wet delay • Time interval: 1 hr; Grid: ~20 km; up to 2 hr prediction • Realized in suite of C, FORTRAN, and Perl programs accessing NOAA tropo. grids via FTP

  11. MODELS / ESTIMATES:CLOSED FORM PREDICTION MODELS • Hopfield: •  (temp., press., wvp.) • Neill m.f. • Saastamoinen: •  (temp., press., wvp., lat., hgt.) • Neill m.f. • WAAS: •  (lat., hgt., doy, U.S. Standard Atmospheres LUT) • Black and Eisner m.f.

  12. INITIAL RESULTS

  13. NOAA ZWD:CONUS

  14. REGIONAL NOAA ZWD:USNO NOAA ZWD - USNO - 25-31 May

  15. REGIONAL NOAA DIFFERENTIAL ZWD:USNO NOAA diff. ZWD - USNO - 25-31 May

  16. REGIONAL NOAA ZWD:NEW ORLEANS

  17. REGIONAL NOAA DIFFERENTIAL ZWD:NEW ORLEANS NOAA diff. ZWD - New Orleans - 25-31 May

  18. MODEL REFERENCE:IGS SINEX – DWH1, WA

  19. MODEL OUTPUTS:USNO, DC

  20. MODEL COMPARISONS: USNO, DC

  21. SINEX-NOAA MODEL COMPARISON: USNO, DC Day of year

  22. SINEX-WAAS MODEL COMPARISON: USNO, DC Day of year

  23. SINEX-SAASTAMOINEN MODEL COMPARISON: USNO, DC Day of year

  24. 14 mm 54 mm 72 mm MODEL COMPARISONS SUMMARY: USNO, DC (38N, 77W, 50m) SINEX - NOAA SINEX - WAAS SINEX - Saas.

  25. 13 mm 80 mm 19 mm MODEL COMPARISONS SUMMARY: GOLD, CA (35N, 117W, 1000m) SINEX - NOAA SINEX - WAAS SINEX - Saas.

  26. 10 mm 28 mm 23 mm MODEL COMPARISONS SUMMARY: PIE1, NM (34N, 108W, 2300m) SINEX - NOAA SINEX - WAAS SINEX - Saas.

  27. 11 mm 20 mm 33 mm MODEL COMPARISONS SUMMARY: AMC2, CO (39N, 105W, 1900m) SINEX - NOAA SINEX - WAAS SINEX - Saas.

  28. 40 mm 39 mm 22 mm MODEL COMPARISONS SUMMARY: DWH1, WA (45N, 122W, 100m) SINEX - NOAA SINEX - WAAS SINEX - Saas.

  29. CONCLUSIONS AND FUTURE WORK

  30. CONCLUSIONS • Taken “first look” at NOAA ZWD decorrelation in space and time • Initial evaluation indicates NOAA ZPD rms of ~1cm, as compared to IGS SINEX tropo. • NOAA ZPD as good or better (few cm) than closed form prediction models, as compared to IGS SINEX tropo.

  31. FUTURE WORK • Range domain analysis: Expand analysis to include more stations and more months of data • Position domain analysis: Apply tropospheric models in undifferenced processing and double-differenced, float processing • Correction output and usage: Devise methods and budgets (precision and data volumes) to supply and use corrections

  32. SUGGESTIONS? • What do you want to see more of? • What’s missing? • …?

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