Validation of Gravity Models from CHAMPGRACE Gravity Missions

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

Validation of Gravity Models from CHAMP/GRACE Gravity Missions Using the GPS/leveling Data from the Continental US Yan M. Wang and D. R. Roman National Geodetic Survey NOAA Potsdam, Germany, July 5 -9, 2004

Overview • • Validate GGM 01 S/C & EIGEN_3 P against 14460 GPS/leveling implied

Overview • • Validate GGM 01 S/C & EIGEN_3 P against 14460 GPS/leveling implied geoid undulations scattered over the U. S. and parts of Canada Compare GGM 01 S/C & EIGEN_3 P 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

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 EGM 96 to degree 360 • GPS/leveling data are converted from NAVD 88 to ITRF 96, then compared with models

Statistics of Differences Units are in cm Model No. of Pts. STD GGM 01

Statistics of Differences Units are in cm Model No. of Pts. STD GGM 01 S (n=120) GGM 01 C (n=200) 14145 47. 3 14181 39. 2 EIGEN_3 P (n=140) 13818 55. 9 (+EGM 96)

Statistics of Differences Units are in cm Model No. of Pts. STD GGM 01

Statistics of Differences Units are in cm Model No. of Pts. STD GGM 01 S (n=90) GGM 01 C (n=90) 14183 36. 5 14182 38. 1 EIGEN_3 P (n=90) 14124 47. 7 (+EGM 96)

Lake Geoid Comparisons Comparison description: • Lake surface is an equipotential surface • 10

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

T/P Tracks Over Lake Superior

Statistics of Differences (Lake Superior) Units are in cm Model (+EGM 96) EGM 96

Statistics of Differences (Lake Superior) Units are in cm Model (+EGM 96) EGM 96 No. of Pts. Mean/RMS 27 0. 231/0. 277 GGM 01 S (N=120) GGM 01 C (N=200) EIGEN_3 P (N=140) 27 0. 149/0. 168 27 0. 159/0. 189 27 -0. 132/0. 159

Statistics of Differences (Lake Superior) Units are in cm Model (+EGM 96) EGM 96

Statistics of Differences (Lake Superior) Units are in cm Model (+EGM 96) EGM 96 No. of Pts. Mean/RMS 27 0. 231/0. 277 GGM 01 S (N=90) GGM 01 C (N=90) EIGEN_3 P (N=90) 27 0. 098/0. 125 27 0. 071/0. 096 27 0. 212/0. 286

T/P Tracks Over Lake Huron

T/P Tracks Over Lake Huron

Statistics of Differences (Lake Huron) Units are in cm Model (+EGM 96) EGM 96

Statistics of Differences (Lake Huron) Units are in cm Model (+EGM 96) EGM 96 No. of Pts. Mean/RMS 31 0. 121/0. 257 GGM 01 S (N=120) GGM 01 C (N=200) EIGEN_3 P (N=140) 31 -0. 300/0. 415 31 -0. 358/0. 406 31 0. 510/0. 644

Statistics of Differences (Lake Huron) Units are in cm Model (+EGM 96) EGM 96

Statistics of Differences (Lake Huron) Units are in cm Model (+EGM 96) EGM 96 No. of Pts. Mean/RMS 31 0. 121/0. 257 GGM 01 S (N=90) GGM 01 C (N=90) EIGEN_3 P (N=90) 31 0. 045/0. 176 31 0. 022/0. 162 31 0. 246/0. 346

Conclusions • Cutoff degree and orders at 90 for all models and augmented by

Conclusions • Cutoff degree and orders at 90 for all models and augmented by EGM 96 to 360 improves the comparisons • GGM 01 S (n<=90)+EGM 96 performs the best in GPS/leveling comparisons • GGM 01 C performs the best in lake surface comparisons • Recommendations: GGM 01 S (n<=90)+EGM 96 is recommended

Web Information • Lake monitoring program supported by USDA: http: //www. pecad. fas. usda.

Web Information • Lake monitoring program supported by USDA: http: //www. pecad. fas. usda. gov/cropexplorer/ global_reservoir

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