hobart australia march 2007willy bertiger ocean surface topography science team meeting gps-based...

Hobart Australia March 2007Willy Bertiger Ocean Surface Topography Science Team Meeting

GPS-Based Precise Orbit Determination: Jason-1 Status

Willy Bertiger, Bruce Haines, Shailen DesaiJet Propulsion Laboratory, California Inst. of Tech., Pasadena CA

Pascal WillisInstitut Geographique National/Institut de Physique du Globe de

Paris, France

March, 2007

Ocean Surface Topography Science Team Meeting

Hobart, Australia


• Better Understanding of GPS Phase Centers based on GRACE Dynamics and Calibrations

• JEM03 – GRACE Static Gravity Field (vs GGM02C)

– AOD1B Release 4 ( vs none )

• Sub-daily density variations in atmosphere, gravitational effect

• ITRF2005 (vs ITRF2000)

Release 07a Incremetal Changes Relative to Release 06b (March 2006)


GRACE As An Antenna Instrument For GPS Trans. Calibration

• Daily precise orbit solutions spanning two years (2004–06)

• One s/c at a time• Dynamical POD to preserve link

between scale and GM

– CD and 1 cpr acc. reset every rev. per UT/CSR approach

• GPS ephemeris and clock offsets fixed to precise values (JPL/IGSAC)

• GRACE antenna a priori PCV model from anechoic chamber:

• 30-sec GPS data– Carrier (LC) only and carrier + code (LC +

PC) solutions performed. No Z apriori• Postfit residuals binned according to az/el of

transmitters.– Least-squares fit to antenna map– Iterate until converged (12XLC, 5XLC/PC)

–15

0

15mm

0

December 11, 2006 BJH 4Fall AGU 2006

mm

-10

+10

GRACE-Based Phase-Center Variation (PCV)

Maps Reveal GPS Antenna Elements

-12

+18

mm

Block II/IIA PCV

Block IIR-B(M) PCV

-10

+10

mm

Block IIA Antenna(Mader and Czopek, 2002)

Block IIR-A PCV

PCV for Ionosphere-free Carrier (LC) with Mean Offset Removed


T/P Radial Antenna Offset Explained

-100

-50

0

50

100

-12

-8

-4

0

4

8

12

1994.0 1996.0 1998.0 2000.0 2002.0 2004.0 2006.0

Time Series of T/P and Jason-1 Radial Antenna Offset EstimatesNoneIGSJPLBCDBCD

Nominal (Gipsy) ModelGRACE-Based GPS PCV Maps

mm

ppb

Year

TOPEX/Poseidon Jason-1

GRACE Data SpanUsed In

PCV Maps

D

-8.2953701Minimum

8.5058155Maximum

0.60300648Sum

19Points

0.031737183Mean

1.1129774Median

4.6419038RMS

4.7689914Std Deviation

22.743279Variance

1.0940817Std Error

-0.039184551Skewness

-0.92282638Kurtosis

Slope = +3.7 ± 0.1 mm/yr

Slope = +0.1 ± 0.1 mm/yr

Bias = +55.6 ± 0.8 mm

B

48.259182Minimum

60.715157Maximum

1056.7383Sum

19Points

55.617803Mean

55.645386Median

55.716286RMS

3.4020173Std Deviation

11.573722Variance

0.78047629Std Error

-0.39930782Skewness

-0.57790671Kurtosis

Bias = +0.0 ± 1.1 mm


JASON Calibration (3 Iterations)

• Dynamic JASON runs 2002-JAN-14 to 2006-JAN-01• Very similar in appearance to release 06b (last year)

Phase Code

-400 400-30 30

mm mm


Release 07a Comparison with GDRB


GDRB-ITRF2000, Rel07a/GSFC-ITRF2005


Reference Frame, Differences with GSFC SLR/DORIS

Model Errors, GPS?Some Pattern with GDRB

-15

-10

-5

0

5

10

15

20 -100

-50

0

50

1000 50 100 150

X MeanY MeanZ Mean

BetaM

ea

n D

iffe

ren

ce

(m

m)

Be

ta (d

eg

ree

s)

Cycle


Geographic Radial Comparison to GDR-B

-16 160

mmmm

Cycles 21-39 Cycles 150-169

RMS: 1.9 mm RMS: 3.5 mm

-16 160

ITRF2000 - 05 Z ~ 11.5ITRF2000 - 05 Z ~ 5.1


Geographic Radial Comparison to GSFC SLR+DORIS

-16 160

mmmm

Cycles 21-39 Cycles 150-169

RMS: 2.9 mm RMS: 3.4 mm

-16 160

GSFC and JPL Rel07a both use ITRF2005


Release 06b - Release 07a

mm

Cycles 141-146

RMS: 1.8 mm

-16 160


Xover Tests


Summary

• Incremental Changes to JPL GPS orbits– Gravity Field, Phase Centers, AOD1B, ITRF2005

• Comparison with GDR-B– Close Performance Measured by crossovers– Slightly better comparison to R06b, Z shift ITRF2005

• Reference Frame Issues ~ cm (Comparison with GSFC SLR/DORIS)– Antenna, Force Models?

• Future Enhancements– Use Solar Panel Quaternions to improve solar pressure– Test other gravity fields, apply time varying solid earth

gravity ( fit to monthly fields )– Improved Albedo Models– Re-tune POD strategy


Backups


Jason Phase Simulation

-30 +30mm

-30 +30

• Simulation/Limitations• Bus Structure -- Flat Plates • Other GPS Antenna -- Disk• Radiometer -- Disk

Empirical 2XSimulation


GPS Transmitter PCV Maps Explain Anomalous Estimated Radial Antenna

Offsets for Jason-1

-50

0

50

-8

-6

-4

-2

0

2

4

6

8

2002.0 2003.0 2004.0 2005.0 2006.0

Time Series of Jason-1 Radial Antenna Offset EstimatesNoneIGSJPLBCD

PPB

PPB

PPB

mm ppb

Year

SVN45SVN47

SVN59SVN60 SVN61SVN56 SVN53

ppb/yrmm/yrppbmmAPPROACH

+0.5+3.7+5.7 +44 Gipsy Nominal (No Maps) +0.0+0.1–2.4 –19 GRACE-Based PCV Maps

BIAS (2004.5) DRIFT

y = m1 + m2*(M0-2004.5)

ErrorValue

0.09989344.073m1

0.0793083.6713m2

NA13240Chisq

NA0.80499R

y = m1 + m2*(M0-2004.5)

ErrorValue

0.099305-31.07m1

0.0788412.4847m2

NA13085Chisq

NA0.67854R

y = m1 + m2*(M0-2004.5)

ErrorValue

0.098676-18.635m1

0.0783410.10805m2

NA12919Chisq

NA0.040391R

y = m1 + m2*(M0-2004.5)

ErrorValue

0.0129735.7237m1

0.01030.47679m2

NA223.31Chisq

NA0.80499R

y = m1 + m2*(M0-2004.5)

ErrorValue

0.012897-4.035m1

0.0102390.32269m2

NA220.69Chisq

NA0.67854R

y = m1 + m2*(M0-2004.5)

ErrorValue

0.012815-2.4201m1

0.0101740.014032m2

NA217.9Chisq

NA0.040391R

Jason-1 Yaw Steering


Improvements Over JPL Release 4, Nov. 2005

Release 04b Release 6.0b

SLR Mean Monthly Variance (mm2)

136 +/- 46 125 +/- 40

SLR Median Monthly RMS (mm)

11.2 10.7

Residuals 65% have smaller monthly residuals

Mean of Daily Radial RMS ( Dynamic – Reduced Dyn) (mm)

10.1 (1376 days) 9.1 (1374 days)

Improved Antenna, Force Models => Re-tune Stochastics, Data weight, Outlier Detection


R06b Comparison to GDR


Reference Frame GDRB vs Rel07b


Release 06b - Release 07a Cycle Mean Z

hobart australia march 2007willy bertiger ocean surface topography science team meeting gps-based...

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