Spherical harmonic models of the shape of the Moon [LOLA]

This archive contains four spherical harmonic models of the shape of the Moon truncated at different maximum spherical harmonic degrees. The highest resolution model has a maximum spherical harmonic degree of 5759, which was generated from a lunar shape model sampled at 64 pixels per degree in the DE421 mean Earth/polar axis coordinate frame.

The data used to generate these models are from the LOLA instrument on the Lunar Reconaissance Orbiter, as found in the file ldem_64_float.img on NASA's PDS website. This image file was first converted to netcdf format using the generic-mapping-tools function xyz2grd, and 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

• Moon_LOLA_shape_5759.bshc.gz
• Moon_LOLA_shape_2879.bshc.gz
• Moon_LOLA_shape_1439.bshc.gz
• Moon_LOLA_shape_719.bshc.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.

Note that this shape model should not be used in conjunction with most gravity models of the Moon. The gravity models use a principal axis coordinate system that differs from the mean Earth/polar axis frame by about 1 km at the equator. For a principal axis coordinate system model, use Spherical harmonic models of the shape of the Moon (principal axis coordinate system).