INITIAL RESULTS FROM AN ANALYSIS OF TROPOSPHERIC CORRECTIONS ON NDGPS
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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


INTRODUCTION


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


EVALUATION METHODOLOGY


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.


INITIAL RESULTS


NOAA ZWD:CONUS


REGIONAL NOAA ZWD:USNO

NOAA ZWD - USNO - 25-31 May


REGIONAL NOAA DIFFERENTIAL ZWD:USNO

NOAA diff. ZWD - USNO - 25-31 May


REGIONAL NOAA ZWD:NEW ORLEANS


REGIONAL NOAA DIFFERENTIAL ZWD:NEW ORLEANS

NOAA diff. ZWD - New Orleans - 25-31 May


MODEL REFERENCE:IGS SINEX – DWH1, WA


MODEL OUTPUTS:USNO, DC


MODEL COMPARISONS: USNO, DC


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 AND FUTURE WORK


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


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