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