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

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

3. INTRODUCTION

4. PROJECT INTRODUCTION Background: 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: 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. TROPOSPHERIC REFRACTION IN GPS tropo delay =  (atmospheric pressure, temperature) +  (water vapor pressure, temperature) 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

6. SPATIOTEMPORAL DECORRELATION “long” baseline 1 k j 2 mf 1 j *zpd 1 j mf 1 k *zpd 1 k mf 2 j *zpd 2 j mf 2 k *zpd 2 k Double-difference slant delay = (mf 1 j * zpd 1 j - mf 1 k * zpd 1 k ) - (mf 2 j * zpd 2 j - mf 2 k * zpd 2 k ) (mf 1 j * zpd 1 j - mf 1 k * zpd 1 k ) - (mf 2 j * zpd 2 j - mf 2 k * zpd 2 k ) “short” baseline 1 k j 2 mf 1 j *zpd 1 j mf 1 k *zpd 1 k mf 2 j *zpd 2 j mf 2 k *zpd 2 k zpd 1 j ~ zpd 2 j ; zpd 1 k ~ zpd 2 k mf 1 j ~ mf 2 j ; mf 1 k ~ mf 2 k mf 1 j ~ mf 2 j ; mf 1 k ~ mf 2 k  slant delay ~ 0  slant delay ~ 0 troposphere

7. EVALUATION METHODOLOGY

8. METHODOLOGY First phase of analysis: range domain evaluations First phase of analysis: range domain evaluations Compare NOAA tropo. corrections against other predictors in space and time 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 GPS-only estimate of ZPD at fixed sites Blended solution from number of int’l organizations Blended solution from number of int’l organizations Estimated precision: < 1 cm  reference solution Estimated precision: < 1 cm  reference solution

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

11. MODELS / ESTIMATES: CLOSED FORM PREDICTION MODELS Hopfield: Hopfield: –  (temp., press., wvp.) –Neill m.f. Saastamoinen: Saastamoinen: –  (temp., press., wvp., lat., hgt.) –Neill m.f. WAAS: 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. MODEL COMPARISONS SUMMARY: USNO, DC (38N, 77W, 50m) SINEX - NOAA SINEX - WAAS SINEX - Saas. 14 mm 54 mm 72 mm

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

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

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

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

29. CONCLUSIONS AND FUTURE WORK

30. CONCLUSIONS Taken “first look” at NOAA ZWD decorrelation in space and time 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. 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. 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 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 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 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 do you want to see more of? What’s missing? What’s missing? …? …?