Spherical harmonic models of the shape of Mars [MOLA]

This archive contains four spherical harmonic models of the shape of Mars truncated at different maximum spherical harmonic degrees. The highest resolution model has a maximum spherical harmonic degree of 5759, which was generated from a Mars shape model sampled at 64 pixels per degree.

The data used to generate these models are from the MOLA instrument on the Mars Global Surveyor spacecraft, as found in the files MEGR00N000GB.IMG, MEGR00N180GB.IMG, MEGR90N000GB.IMG and MEGR90N180GM.IMG on NASA's PDS website. These four image files were first converted to netcdf format using the generic-mapping-tools function xyz2grd, and then turned into a single file using the function grdpaste. The resulting pixel registed map was then converted to a gridline registration using the function grdsample. Following this, the resulting netcdf file was read into the pyshtools software and expanded into spherical harmonics using the function SHCoeffs.expand(). The spherical harmonic functions were chosen to be "4pi" normalized and to exclude the Condon-Shortley phase factor of (-1)^m. The units of the coefficients are meters.

The four files in this archive are

• Mars_shape_5759.sh.gz
• Mars_shape_2879.sh.gz
• Mars_shape_1439.sh.gz
• Mars_shape_719.sh.gz

The numbers 5759, 2879, 1439, and 719 in the filename refer to the maximum spherical harmonic degree of file, which corresponds to effective spatial resolutions of 64, 32, 16, and 8 pixels per degree, respectively. The files are stored in the binary "bshc" format as described in the pyshtools documentation and are furthermore compressed using gzip. The lower resolution models were generated by truncating the spherical harmonic coefficients of the highest resolution model.

These models supercede Spherical harmonic model of the shape of Mars: MarsTopo2600 and Spherical harmonic model of the shape of Mars: MarsTopo719.