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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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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 • Project introduction • Evaluation methodology • Initial results • Conclusions and future work
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
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)
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
METHODOLOGY • First phase of analysis: range domain evaluations • Compare NOAA tropo. corrections against other predictors in space and time
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
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
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.
REGIONAL NOAA ZWD:USNO NOAA ZWD - USNO - 25-31 May
REGIONAL NOAA DIFFERENTIAL ZWD:USNO NOAA diff. ZWD - USNO - 25-31 May
REGIONAL NOAA DIFFERENTIAL ZWD:NEW ORLEANS NOAA diff. ZWD - New Orleans - 25-31 May
SINEX-NOAA MODEL COMPARISON: USNO, DC Day of year
SINEX-WAAS MODEL COMPARISON: USNO, DC Day of year
SINEX-SAASTAMOINEN MODEL COMPARISON: USNO, DC Day of year
14 mm 54 mm 72 mm MODEL COMPARISONS SUMMARY: USNO, DC (38N, 77W, 50m) SINEX - NOAA SINEX - WAAS SINEX - Saas.
13 mm 80 mm 19 mm MODEL COMPARISONS SUMMARY: GOLD, CA (35N, 117W, 1000m) SINEX - NOAA SINEX - WAAS SINEX - Saas.
10 mm 28 mm 23 mm MODEL COMPARISONS SUMMARY: PIE1, NM (34N, 108W, 2300m) SINEX - NOAA SINEX - WAAS SINEX - Saas.
11 mm 20 mm 33 mm MODEL COMPARISONS SUMMARY: AMC2, CO (39N, 105W, 1900m) SINEX - NOAA SINEX - WAAS SINEX - Saas.
40 mm 39 mm 22 mm MODEL COMPARISONS SUMMARY: DWH1, WA (45N, 122W, 100m) SINEX - NOAA SINEX - WAAS SINEX - Saas.
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.
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
SUGGESTIONS? • What do you want to see more of? • What’s missing? • …?