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The GEM-T2 gravitational modelThe GEM-T2 is the latest in a series of Goddard Earth Models of the terrestrial field. It was designed to bring modeling capabilities one step closer towards ultimately determining the TOPEX/Poseidon satellite's radial position to an accuracy of 10-cm RMS (root mean square). It also improves models of the long wavelength geoid to support many oceanographic and geophysical applications. The GEM-T2 extends the spherical harmonic field to include more than 600 coefficients above degree 36 (which was the limit for its predecessor, GEM-T1). Like GEM-T1, it was produced entirely from satellite tracking data, but it now uses nearly twice as many satellites (31 vs. 17), contains four times the number of observations (2.4 million), has twice the number of data arcs (1132), and utilizes precise laser tracking from 11 satellites. The estimation technique for the solution has been augmented to include an optimum data weighting procedure with automatic error calibration for the gravitational parameters. Results for the GEM-T2 error calibration indicate significant improvement over previous satellite-only models. The error of commission in determining the geoid has been reduced from 155 cm in GEM-T1 to 105 cm for GEM-T2 for the 36 x 36 portion of the field, and 141 cm for the entire model. The orbital accuracies achieved using GEM-T2 are likewise improved. Also, the projected radial error on the TOPEX satellite orbit indicates 9.4 cm RMS for GEM-T2, compared to 24.1 cm for GEM-T1.
Document ID
19900003668
Acquisition Source
Legacy CDMS
Document Type
Technical Memorandum (TM)
Authors
Marsh, J. G. (NASA Goddard Space Flight Center Greenbelt, MD., United States)
Lerch, F. J. (NASA Goddard Space Flight Center Greenbelt, MD., United States)
Putney, B. H. (NASA Goddard Space Flight Center Greenbelt, MD., United States)
Felsentreger, T. L. (NASA Goddard Space Flight Center Greenbelt, MD., United States)
Sanchez, B. V. (NASA Goddard Space Flight Center Greenbelt, MD., United States)
Klosko, S. M. (ST Systems Corp. Lanham, MD., United States)
Patel, G. B. (ST Systems Corp. Lanham, MD., United States)
Robbins, J. W. (ST Systems Corp. Lanham, MD., United States)
Williamson, R. G. (ST Systems Corp. Lanham, MD., United States)
Engelis, T. E. (ST Systems Corp. Lanham, MD., United States)
Date Acquired
September 6, 2013
Publication Date
October 1, 1989
Subject Category
Geophysics
Report/Patent Number
REPT-89B00244
NAS 1.15:100746
NASA-TM-100746
Accession Number
90N12984
Funding Number(s)
PROJECT: RTOP 414-70-75-25
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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