Geoid improvement over Alaska/Yukon area by GRACE and GOCE models

X Li1, JL Huang2, YM Wang3, M Véronneau2, D Roman3

1ERT Inc USA2Geodetic Survey Division, CCRS, NRCan, Canada3National Geodetic Survey, NOAA, USA

European Geosciences Union, General Assembly 2012Vienna | Austria | 22 – 27 April 2012

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Outline

• Objectives

• Data sets used

• GRACE/GOCE gravity models comparison with GPS/leveling data in Alaska/Yukon area

• Improvement in local geoid computation by combing surface gravity data

• Conclusions

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Objectives

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• To assess the improvement of GRACE/GOCE satellite gravity models over EGM08 in the Alaska/Yukon area

• To examine the improvement of GRACE/GOCE satellite gravity models in local geoid computation based on the method of remove-restore and kernel modification

Data used

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• Surface gravity data: 544,957– 457,477(NGS)+74,933(GSD)+12,547(NGA)

• 3,265,928 (DNSC08) altimetric gravity anomaly• 95 and 90 GPS/leveling data in Alaska and Yukon,

respectively• Sea surface topography model from Foreman et al 2008• Global gravity models used:

1. TIM (Time-wise solution GO_CONS_GCF_2_TIM_R3)2. DIR (Direct solution GO_CONS_GCF_2_DIR_R3)3. GOCO02s4. EIGEN_6c 5. EGM086. CGG10 (Canada)

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GRACE/GOCE gravity models comparison with GPS/leveling data

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)()(max

0 0

nmnm

N

n

n

m

nmnmn

PPcomb SbRa

r

a

r

GMV

inm

inm

EGMnm

EGMnm

nm

nm

b

aw

b

aw

b

a)1(

08

08

• To avoid leakage of high frequency, only combined models (cut/paste) used

where

Weight function used (10&60 degree)

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Mean geoid difference by degree(h – H) – N

8

STD of Geoid difference by degree(h – H) – N

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EIGEN_6c (10 degree c/p window)

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EIGEN_6c (zoom in)

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Eigen_6c and EGM08

N = MSSH(DNSC08) – SST(Foreman)

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(MSSH – SST) – N(Combined models)

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Local Geoid (Stokes-Helmert Method)

PITEH NNW

R

MGN

'EGM~1,H

TGHMDB

GOCE~1,HH

'0

maxmax)(

4

dggSR

NN nn

Helmert co-geoid height:

5520

2MDB )(cos

1

12)(

nnn P

n

nS

Geoid height:

Low-degree components:

DTE~1,H

2 EE

GOCE~1,H max

max

max)( n

n

nmnmnm

n

n

n

n NYCr

a

r

GMN

DTE~2,H

2 E2

E

GOCE~1,H max

max

max)()1( n

n

nmnmnm

n

n

n

n AYCnr

a

r

GMg

Modification of the Degree-Banded Stokes kernel:

Weight function and its spectral

vnnnnnv

nnL

LnuLuLnu

n

maxmaxmax

max

1,1)(cos5.0

11

,1)(cos5.0

)(2

1)( 0

MDB0 nnn Q

n

Modification coefficients (Huang and Véronneau 2012) :

Spectral transfer functions:

6 MDB

MDB sin)(cos)( dPSQ nn

Truncation error coefficients:

50 100 150 200-0.2

0

0.2

0.4

0.6

0.8

1

S pherica l Harmonic Degree n

n

5300 5400 5500 5600-0.2

0

0.2

0.4

0.6

0.8

1

S pherica l Harmonic Degree n

n

50 100 150 200-0.2

0

0.2

0.4

0.6

0.8

1

S pherica l Harmonic Degree n

n

0=6

5300 5400 5500 5600-0.2

0

0.2

0.4

0.6

0.8

1

S pherica l Harmonic Degree n

n

0=6

L=150LE=L-u/2

GPS/Levelling Test 1

93 GPS and leveling stations 90 GPS and leveling stations

Conclusions (1)• There is no noticeable improvement in GPS/leveling comparisons in Alaska (crustal motion, subsidence, PGR. etc.)

• . GPS/leveling (Yukon) comparison shows the improvement of satellite models over EGM08 happens between degree 80 to 195.

• 3 cm (21 to 18 cm) improvement of EIGEN_6c over EGM08 is seen at degree 195. There is no improvement after degree 1000. EGM08 does not improve after degree 1000, too.

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Conclusions (2)

• GOCO02s seems more accurate than other solutions between degree 130 to 195.

• Coefficients of all satellite models after degree 195 seem to degrade significantly and are not useable

• Altimetric geoid comparisons show the improvement between degree 105 to 160.

• Local geoid comparisons show a similar pattern

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