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 0nmnm
N
n
n
mnmnm
n
PPcomb SbRa
ra
rGMV
inm
inm
EGMnm
EGMnm
nm
nm
ba
wba
wba
)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
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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 NNWRMGN
'EGM~1,H
TGHMDB
GOCE~1,HH
'0
maxmax)(
4
dggSRNN nn
Helmert co-geoid height:
5520
2MDB )(cos
112)(
nnn P
nnS
Geoid height:
Low-degree components:
DTE~1,H
2 EE
GOCE~1,H max
max
max)( n
n
nmnmnm
n
n
n
n NYCra
rGMN
DTE~2,H
2 E2
E
GOCE~1,H max
max
max)()1( n
n
nmnmnm
n
n
n
n AYCnra
rGMg
Modification of the Degree-Banded Stokes kernel:
Weight function and its spectral
vnnnnnv
nnL
LnuLuLnu
n
maxmaxmax
max
1,1)(cos5.0
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,1)(cos5.0
)(2
1)( 0MDB
0 nnn Qn
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
Spherica l Harmonic Degree n
n
5300 5400 5500 5600-0.2
0
0.2
0.4
0.6
0.8
1
Spherica l Harmonic Degree n
n
50 100 150 200-0.2
0
0.2
0.4
0.6
0.8
1
Spherica 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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