A gravity model for crustal dynamics (GEM‐L2)

Publisher Website
Google Scholar
Abstract
Goddard earth model, GEM‐L2, has been derived using predominantly the precise laser ranging taken on many satellites, including LAGEOS, in support of NASA's crustal dynamics activities. Only conventional satellite tracking (ground to satellite: GEM 9's data plus LAGEOS ranging) has been employed. The solution consists of 566 gravitational harmonic coefficients (complete through degree 20) and the earth‐fixed coordinates of 173 tracking stations including about 20 used exclusively for LAGEOS. In addition, 5‐day averages of earth orientations (pole position and length of day) have been derived simultaneously from the LAGEOS data for 1979–1981. These latter results have been independently confirmed by very long baseline interferometric observations. The model improves the utility of the LAGEOS data for detecting global movements of the crust and earth orientation while also enhancing our understanding of the long‐wavelength gravity field. In addition to the LAGEOS data, the solution combined laser ranging from nine satellites and optical and electronic measurements on some 20 spacecraft for a total of 1,257,000 observations. GEM‐L2 has improved the modeling of the longest‐wavelength portion of the field by more than a factor of 2 over GEM's developed in the late 1970's. A full discussion of GEM‐L2's accuracy is found elsewhere in this issue. Use of GEM‐L2 yields smaller LAGEOS positioning errors from about 1 m with GEM 9 (1979) to a current value of about 25 cm.