Spherical harmonic models of the shape of Mercury

The data used to generate these spherical harmonic models is the global digital elevation model (DEM) of Mercury. The DEM is derived from observations made by the Mercury Dual Imaging System (MDIS) narrow-angle camera (NAC) and multispectral wide-angle camera (WAC) on board of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. 

The global DEM was downloaded throught the Astropedia catalog in geoTIFF format and equirectangular projection.  Using the rasterio package, the dataset was loaded in python, scaled to the local height and radius (described in the Astropedia documentation), and exported into .dat format. Then, the file was converted into a netcdf format and resampled into a gridline registration using the generic-mapping-tools  as follows:gmt xyz2grd filename.dat -Gfilename.grd -R0/360/-90/90 -I0.015625/0.015625 -ZTLd -fg -rpgmt grdsample filename.grd -Gfilename_gridline.grd -T

The resulting netcdf file was read into the pyshtools software with the SHGrid.from_netcdf() and expanded into spherical harmonics using the function SHGrid.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

- Mercury_shape_5759.sh.gz- Mercury_shape_2879.sh.gz- Mercury_shape_1439.sh.gz- Mercury_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.

The spherical harmonic coefficients can be loaded with pyshtools as follows:SHCoeffs.from_file("filename.sh.gz", format='bshc')