Venus gravity: 180th degree and order model

The Magellan Doppler radiometric tracking data provides unprecedented precision for spacecraft-based gravity measurements with the maximum resolution approaching spherical harmonic degree and order 180 in selected equatorial regions. Determining a gravity field to degree 180 with a complete covariance containing the correlations between all the spherical harmonic coefficients (a 4.5-GB binary file for the triangular matrix) would be an extensive computational task even on the JPL/Caltech supercomputer that we used. Instead we determined a gravity field complete to degree and order 180 but in three separate steps. This gravity solution (MGNP180U) was determined first to degree and order 120 with a complete covariance for all the coefficients to degree 120. The second step solved far the coefficients from degree 116 to 155 only and the third step from degree 154 to 180. MGNP180U shows substantial improvement over previous solutions (up to and including MGNP120PSAAP, A. S. Konopliv et al. 1996a, presented at 1996 AGU Fall Meeting, San Francisco, CA) especially in the medium to shorter wavelengths (harmonic degree 80 and greater). The RMS magnitude power in the spectrum has increased as well as the correlations with topography, The amplitudes of various features have increased substantially (up to 33%, e.g., Bell Regio and Maat Mons). This will allow for better investigation of lithospheric modeling for shorter wavelength features such as coronae, volcanoes, and impact basins, (C) 1999 Academic Press.