100 likes | 216 Views
Recent Geoid Research at NGS. Dru A. Smith. Status of various tasks. Helmert Anomalies Terrain Modeling Density Modeling Downward Continuation Improved Theory Ellipsoidal BVP Combination of GPS/geoid/leveling. Overall Status. Spherical DEM, Outer Zone: 95%
E N D
Recent Geoid Research at NGS Dru A. Smith
Status of various tasks • Helmert Anomalies • Terrain Modeling • Density Modeling • Downward Continuation • Improved Theory • Ellipsoidal BVP • Combination of GPS/geoid/leveling
Overall Status • Spherical DEM, Outer Zone: 95% • Spherical DEM, Inner Zone: 25% • Ellipsoidal DEM: Ongoing (D. Smith) • Density Modeling: No action • Downward Continuation: No action • Ellipsoidal: Accepted Fei/Sideris. Working on similar one-step approach. • Data Combination: Ongoing (D. Roman)
Spherical DEM, Outer Zone, I • Uses Global 5’ DEM and 1-D FFT • 160 wall-clock hours on 2 Ultra 2s for attraction of 3-D masses computed at surface of Earth outside a 4 degree cap • sub-microGal accuracy, terms to h4 • 30 arcsecond test in progress
Spherical DEM, Outer Zone, II • Any cap size can be chosen • Space domain validations are in progress • Similar approach will be used for attraction of condensed masses (computed at Earth’s surface or at geoid) and for potential changes (I.e. the Indirect effect)
Spherical DEM, Inner Zone • One paper through review at JG • Space Domain • Mix of 1” and 30” DEM • Maui Supercomputer for final CONUS run
Ellipsoidal DEM • Recently begun • Computations to show how much is improved over spherical DEM
Ellipsoidal Theory • Fei and Sideris, 2000 (JoG) • Compute spherical N, then compute corrections • Appears to reduce N/S tilts wrt GPSBMs by 50% • Investigating other approaches (I.e. “4th” fundamental BVP?)
Combination Theory • Non-isotropic, non-homogenous nature of covariance function • Non-homogenous nature of USA GPS HARN surveys • Difficult to get full VCV matrices • Leveling in archives • Correlation between state-by-state GPS surveys
Next Steps, in order: • Outer Zone • Inner Zone • Combination Theory • Ellipsoidal DEM • Downward Continuation • No new geoid in 2000