Sunil Bisnath and David Dodd Sunil Bisnath and David Dodd

Hydrographic Science Research Center,Hydrographic Science Research Center,

Department of Marine Science, University of Southern MississippiDepartment of Marine Science, University of Southern Mississippi

USCG C2CEN MeetingUSCG C2CEN Meeting

15-17 June, Portsmouth, Virginia15-17 June, Portsmouth, Virginia

INITIAL RESULTS FROM AN ANALYSIS OF INITIAL RESULTS FROM AN ANALYSIS OF TROPOSPHERIC CORRECTIONS ON NDGPSTROPOSPHERIC CORRECTIONS ON NDGPS

OVERVIEW OF PRESENTATIONOVERVIEW OF PRESENTATION

• Project introductionProject introduction

• Evaluation methodologyEvaluation methodology

• Initial resultsInitial results

• Conclusions and future workConclusions and future work

INTRODUCTIONINTRODUCTION

PROJECT INTRODUCTIONPROJECT INTRODUCTION

• Background:Background:

– For NDGPS to meet higher accuracy demands, For NDGPS to meet higher accuracy demands, tropospheric delay modeling (along with other error tropospheric delay modeling (along with other error handling) must be significantly improvedhandling) must be significantly improved

– NOAA has developed a conventional / GPS tropospheric NOAA has developed a conventional / GPS tropospheric model model

• Objectives:Objectives:

– An independent, extensive analysis of NOAA modelAn independent, extensive analysis of NOAA model

– Analysis of improvement in GPS data processing resultsAnalysis of improvement in GPS data processing results

– Analysis of how data can be delivered and appliedAnalysis of how data can be delivered and applied

TROPOSPHERIC REFRACTION IN GPSTROPOSPHERIC REFRACTION IN GPS

tropo delaytropo delay==

(atmospheric pressure, temperature)(atmospheric pressure, temperature)++

(water vapor pressure, temperature)(water vapor pressure, temperature)

hydrostatic or “dry” delayhydrostatic or “dry” delay

wet delaywet delay

~ 90% of total delay / e.g., 180 cm / mostly predictable~ 90% of total delay / e.g., 180 cm / mostly predictable

~ 10% of total delay / e.g., 20 cm / ~ 10% of total delay / e.g., 20 cm / very irregularvery irregular

SPATIOTEMPORAL DECORRELATIONSPATIOTEMPORAL DECORRELATION

“long” baseline

1

k

j

2

mfmf11jj*zpd*zpd11

jj

mfmf11kk*zpd*zpd11

kk

mfmf22jj*zpd*zpd22

jj

mfmf22kk*zpd*zpd22

kk

Double-difference slant delay =Double-difference slant delay = (mf(mf11

j j * zpd* zpd11jj - mf - mf11

k k * zpd* zpd11kk) - ) -

(mf(mf22j j * zpd* zpd22

jj - mf - mf22k k * zpd* zpd22

kk))

“short” baseline

1

k

j

2

mfmf11jj*zpd*zpd11

jj

mfmf11kk*zpd*zpd11

kk

mfmf22jj*zpd*zpd22

jj

mfmf22kk*zpd*zpd22

kk

zpdzpd11jj ~ zpd ~ zpd22

jj ; zpd ; zpd11kk ~ zpd ~ zpd22

kk

mfmf11jj ~ mf ~ mf22

jj ; mf ; mf11kk ~ mf ~ mf22

kk

slant delay ~ 0 slant delay ~ 0

troposphere

EVALUATION METHODOLOGYEVALUATION METHODOLOGY

METHODOLOGYMETHODOLOGY

• First phase of analysis:First phase of analysis: range domain evaluations range domain evaluations

• Compare NOAA tropo. corrections against other Compare NOAA tropo. corrections against other predictors in space and timepredictors in space and time

MODELS / ESTIMATES:MODELS / ESTIMATES:IGS SINEX PRODUCTIGS SINEX PRODUCT

• GPS-only estimate of ZPD at fixed sitesGPS-only estimate of ZPD at fixed sites

• Blended solution from number of int’l organizationsBlended solution from number of int’l organizations

• Estimated precision: Estimated precision: < 1 cm< 1 cm reference solutionreference solution

MODELS / ESTIMATES:MODELS / ESTIMATES:NOAA TROPOSPHERIC PRODUCTNOAA TROPOSPHERIC PRODUCT

• Developed by Forecast Systems Lab, NOAADeveloped by Forecast Systems Lab, NOAA

• http://www.gpsmet.noaa.govhttp://www.gpsmet.noaa.gov

• Numerical weather prediction model output using Numerical weather prediction model output using GPS data assimilated from CONUSGPS data assimilated from CONUS

• Input:Input: lat., long., ell. hgt., time lat., long., ell. hgt., time

• Output:Output: zenith hydrostatic delay and zenith wet delay zenith hydrostatic delay and zenith wet delay

• Time interval: 1 hr; Grid: ~20 km; up to 2 hr predictionTime interval: 1 hr; Grid: ~20 km; up to 2 hr prediction

• Realized in suite of C, FORTRAN, and Perl programs Realized in suite of C, FORTRAN, and Perl programs accessing NOAA tropo. grids via FTPaccessing NOAA tropo. grids via FTP

MODELS / ESTIMATES:MODELS / ESTIMATES:CLOSED FORM PREDICTION MODELSCLOSED FORM PREDICTION MODELS

• Hopfield:Hopfield:

(temp., press., wvp.)(temp., press., wvp.)

– Neill m.f.Neill m.f.

• Saastamoinen:Saastamoinen:

(temp., press., wvp., lat., hgt.)(temp., press., wvp., lat., hgt.)

– Neill m.f.Neill m.f.

• WAAS:WAAS:

(lat., hgt., doy, U.S. Standard Atmospheres LUT)(lat., hgt., doy, U.S. Standard Atmospheres LUT)

– Black and Eisner m.f.Black and Eisner m.f.

INITIAL RESULTSINITIAL RESULTS

NOAA ZWD:NOAA ZWD:CONUSCONUS

REGIONAL NOAA ZWD:REGIONAL NOAA ZWD:USNOUSNO

NOAA ZWD - USNO - 25-31 May

REGIONAL NOAA DIFFERENTIAL ZWD:REGIONAL NOAA DIFFERENTIAL ZWD:USNOUSNO

NOAA diff. ZWD - USNO - 25-31 May

REGIONAL NOAA ZWD:REGIONAL NOAA ZWD:NEW ORLEANSNEW ORLEANS

REGIONAL NOAA DIFFERENTIAL ZWD:REGIONAL NOAA DIFFERENTIAL ZWD:NEW ORLEANSNEW ORLEANS

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

MODEL REFERENCE:MODEL REFERENCE:IGS SINEX – DWH1, WAIGS SINEX – DWH1, WA

MODEL OUTPUTS:MODEL OUTPUTS:USNO, DCUSNO, DC

MODEL COMPARISONS:MODEL COMPARISONS: USNO, DC USNO, DC

SINEX-NOAA MODEL COMPARISON:SINEX-NOAA MODEL COMPARISON: USNO, DC USNO, DC

Day of year

SINEX-WAAS MODEL COMPARISON:SINEX-WAAS MODEL COMPARISON: USNO, DC USNO, DC

Day of year

SINEX-SAASTAMOINEN MODEL COMPARISON:SINEX-SAASTAMOINEN MODEL COMPARISON: USNO, DC USNO, DC

Day of year

MODEL COMPARISONS SUMMARY:MODEL COMPARISONS SUMMARY: USNO, DC (38N, 77W, 50m) USNO, DC (38N, 77W, 50m)

SINEX- NOAA

SINEX- WAAS

SINEX- Saas.

14 mm

54 mm

72 mm

MODEL COMPARISONS SUMMARY:MODEL COMPARISONS SUMMARY: GOLD, CA (35N, 117W, 1000m) GOLD, CA (35N, 117W, 1000m)

SINEX- NOAA

SINEX- WAAS

SINEX- Saas.

13 mm

80 mm

19 mm

MODEL COMPARISONS SUMMARY:MODEL COMPARISONS SUMMARY: PIE1, NM (34N, 108W, 2300m) PIE1, NM (34N, 108W, 2300m)

SINEX- NOAA

SINEX- WAAS

SINEX- Saas.

10 mm

28 mm

23 mm

MODEL COMPARISONS SUMMARY:MODEL COMPARISONS SUMMARY: AMC2, CO (39N, 105W, 1900m) AMC2, CO (39N, 105W, 1900m)

SINEX- NOAA

SINEX- WAAS

SINEX- Saas.

11 mm

20 mm

33 mm

MODEL COMPARISONS SUMMARY:MODEL COMPARISONS SUMMARY: DWH1, WA (45N, 122W, 100m) DWH1, WA (45N, 122W, 100m)

SINEX- NOAA

SINEX- WAAS

SINEX- Saas.

40 mm

39 mm

22 mm

CONCLUSIONS AND FUTURE WORKCONCLUSIONS AND FUTURE WORK

CONCLUSIONSCONCLUSIONS

• Taken “first look” at NOAA ZWD decorrelation in Taken “first look” at NOAA ZWD decorrelation in space and timespace and time

• Initial evaluation indicates NOAA ZPD rms of ~1cm, Initial evaluation indicates NOAA ZPD rms of ~1cm, as compared to IGS SINEX tropo.as compared to IGS SINEX tropo.

• NOAA ZPD as good or better (few cm) than closed NOAA ZPD as good or better (few cm) than closed form prediction models, as compared to IGS SINEX form prediction models, as compared to IGS SINEX tropo.tropo.

FUTURE WORKFUTURE WORK

• Range domain analysis:Range domain analysis: Expand analysis to include Expand analysis to include more stations and more months of datamore stations and more months of data

• Position domain analysis:Position domain analysis: Apply tropospheric models Apply tropospheric models in undifferenced processing and double-differenced, in undifferenced processing and double-differenced, float processingfloat processing

• Correction output and usage:Correction output and usage: Devise methods and Devise methods and budgets (precision and data volumes) to supply and budgets (precision and data volumes) to supply and use correctionsuse corrections

SUGGESTIONS?SUGGESTIONS?

• What do you want to see more of?What do you want to see more of?

• What’s missing?What’s missing?

• ……??