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GGG 2000, Session 9 The Challenge of the cm-geoid. August 4, 2000 12:10-12:30. Recent Investigations Towards Achieving a One Centimeter Geoid. Daniel R. Roman & Dru A. Smith U.S. National Geodetic Survey. OUTLINE. G99SSS/GEOID99 processing stream Refinements of hybrid methodology
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GGG 2000, Session 9 The Challenge of the cm-geoid August 4, 2000 12:10-12:30 Recent Investigations Towards Achieving a One Centimeter Geoid Daniel R. Roman & Dru A. Smith U.S. National Geodetic Survey
OUTLINE • G99SSS/GEOID99 processing stream • Refinements of hybrid methodology • Development of a direct Helmert approach • Other future developments
G99SSS/GEOID99 Processing Stream • Use of Faye anomalies in G99SSS is same as approach taken for G96SSS (GEOID96) • Higher resolution DEM in PNW increased calculated terrain correction (TC) signal • TC’s calculated in much narrower bands • More GPS on BM data improved regions previously under-represented (Midwest & Plains States) in GEOID96
Refinements of Hybrid Methodology • G99SSS & GPS on BM residuals were modeled both by minimum curvature with a 300-km low-pass filter and by iterative LSC at 550 & 33 km correlation lengths • Forthcoming models will be based on single-pass LSC using a 33 km correlation length and use of non-uniform sigma values based on GPS network accuracies
Development of a Direct Helmert Approach • Terrain Effects broken into inner ( <4 degrees) and outer ( >4 degrees) zones • Outer zone is being modeled using FFT’s • Inner zone will be modeled in spherical coordinates in the space domain • Merging will be with an equivalent taper applied in both space & frequency domains • Downward continuation consistent with terrain effects is being explored
Other Future Developments • Development of a North American geoid • Impending satellite gravity missions • Anticipated improvements to observations and DEM’s
Development of North American Geoid • Joint (U.S., Canadian, Mexico, etc.) effort • Anticipated scope is from the North Pole to the Equator including Greenland & Alaska • Next NAG subcomm. meeting possibly in Mexico, Central America or Caribbean • Largest obstacle remaining: Data gaps in Central America and Cuba
Impending Satellite Gravity Missions • GRACE, CHAMP, & GOCE • Expect cm-level commission errors for the resulting degree 120-250 harmonic models • Combining these models with surface gravity observations should produce high-resolution geoid at the cm-level • May eliminate the need for hybrid geoids and permit analysis of leveling networks
Anticipated Improvements to Observations and DEM’s • National Adjustment of CORS Network in 2004 will create more cohesive GPS-derived ellipsoidal heights at bench marks • Increased DEM resolution (1 arc-second for all of CONUS) will improve determination of 3D masses beneath gravity observations
Conclusion • Ongoing research will improve current approach (near term) and develop avenues for more rigorous solutions (far term) • Expected quality and quantity of future DEM and satellite gravity data sets should complement the theoretical improvements • Development of a joint regional gravimetric geoid will enhance international studies