Validation of Gravity Models from CHAMP/GRACE Gravity Missions Using the GPS/leveling Data from

the Continental USYan M. Wang and D.R. Roman

National Geodetic SurveyNOAA

Potsdam, Germany, July 5-9, 2004

Overview

• Validate GGM01S/C & EIGEN_3P against 14460 GPS/leveling implied geoid undulations scattered over the U.S. and parts of Canada

• Compare GGM01S/C & EIGEN_3P to geoid changes deduced from 10 years of TOPEX/Poseidon altimetry data over the Great Lakes

GPS/leveling Comparisons

Comparison description:

• Geoid is computed from coefficient models in full degree and order and to degree and order 90, then augmented with EGM96 to degree 360

• GPS/leveling data are converted from NAVD88 to ITRF96, then compared with models

Statistics of DifferencesUnits are in cm

Model (+EGM96)

No. of Pts. STD

GGM01S

(n=120)

14145 47.3

GGM01C

(n=200)

14181 39.2

EIGEN_3P

(n=140)

13818 55.9

Statistics of DifferencesUnits are in cm

Model (+EGM96)

No. of Pts. STD

GGM01S

(n=90)

14183 36.5

GGM01C

(n=90)

14182 38.1

EIGEN_3P

(n=90)

14124 47.7

Lake Geoid Comparisons

Comparison description:

• Lake surface is an equipotential surface

• 10 years of TOPEX/Poseidon altimeter data provide accurate mean lake surface with 2-3 cm accuracy (Beckley, private communication)

• Geoid changes are compared over two tracks (Lake Superior and Huron)

T/P Tracks Over Lake Superior

Geoid Changes (Lake Superior)

-2

-1.5

-1

-0.5

0

0.5

1

0 50 100 150 200

Distance (S/N, km)

Met

er

N(alt.)

N(EGM96)

N(GGM01S)

N(GGM01C)

N(EIGN_3P)

res.(N(EGM96)

res.(GGM01S)

res.(GGM01C)

res.(EIGN_3P)

Statistics of Differences(Lake Superior) Units are in cm

Model

(+EGM96)No. of Pts. Mean/RMS

EGM96 27 0.231/0.277

GGM01S(N=120)

27 0.149/0.168

GGM01C(N=200)

27 0.159/0.189

EIGEN_3P(N=140)

27 -0.132/0.159

Statistics of Differences(Lake Superior) Units are in cm

Model

(+EGM96)No. of Pts. Mean/RMS

EGM96 27 0.231/0.277

GGM01S(N=90)

27 0.098/0.125

GGM01C(N=90)

27 0.071/0.096

EIGEN_3P(N=90)

27 0.212/0.286

T/P Tracks Over Lake Huron

Geoid Changes (Lake Huron)

-1.5

-1

-0.5

0

0.5

1

0 50 100 150 200

Distance (N/S, km)

Met

er

N(alt.)

N(EGM96)

N(GGM01S)

N(GGM01C)

N(EIGN_3P)

res.(N(EGM96)

res.(GGM01S)

res.(GGM01C)

res.(EIGN_3P)

Statistics of Differences(Lake Huron) Units are in cm

Model

(+EGM96)No. of Pts. Mean/RMS

EGM96 31 0.121/0.257

GGM01S(N=120)

31 -0.300/0.415

GGM01C(N=200)

31 -0.358/0.406

EIGEN_3P(N=140)

31 0.510/0.644

Statistics of Differences(Lake Huron) Units are in cm

Model

(+EGM96)No. of Pts. Mean/RMS

EGM96 31 0.121/0.257

GGM01S(N=90)

31 0.045/0.176

GGM01C(N=90)

31 0.022/0.162

EIGEN_3P(N=90)

31 0.246/0.346

Conclusions

• Cutoff degree and orders at 90 for all models and augmented by EGM96 to 360 improves the comparisons

• GGM01S (n<=90)+EGM96 performs the best in GPS/leveling comparisons

• GGM01C performs the best in lake surface comparisons

• Recommendations: GGM01S (n<=90)+EGM96 is recommended

Web Information

• Lake monitoring program supported by USDA:

http://www.pecad.fas.usda.gov/cropexplorer/global_reservoir