Spherical harmonic models of the shape of the Moon (principal axis coordinate system) [LDEM128]

This archive contains five spherical harmonic models of the shape of the Moon in a principal axis coordinate system, truncated at different maximum spherical harmonic degrees. The highest resolution model has a maximum spherical harmonic degree of 11519, which was generated from a lunar shape model sampled at 128 pixels per degree.

The dataset used to generate these models is the file LDEM128_PA_gridline_202405.grd. As described by Neumann (2024), this shape mode is based on a combination of laser altimeter data obtained by the LOLA instrument on the Lunar Reconaissance Orbiter spacecraft and the SLDEM2015 shape model that makes use of both LOLA and Kaguya terrain camera data. The 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 five files in this archive are

• Moon_LDEM128_shape_pa_11519.sh.gz
• Moon_LDEM128_shape_pa_5759.sh.gz
• Moon_LDEM128_shape_pa_2879.sh.gz
• Moon_LDEM128_shape_pa_1439.sh.gz
• Moon_LDEM128_shape_pa_719.sh.gz

The numbers 11519, 5759, 2879, 1439, and 719 in the filename refer to the maximum spherical harmonic degree of file, which corresponds to effective spatial resolutions of 128, 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.

This shape model uses the same coordinate system as most lunar gravity models. The principal axis coordinate system differs from the more common mean Earth/polar axis system by about 1 km at the equator. For a mean Earth/polar axis model, use Spherical harmonic models of the shape of the Moon.