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

This archive contains four 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 5759, which was generated from a lunar shape model sampled at 64 pixels per degree.

The data used to generate these models are from the LOLA instrument on the Lunar Reconaissance Orbiter, as found in the file ldem_64_pa.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 gridline-registered 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_pa_5759.bshc.gz
• Moon_LOLA_shape_pa_2879.bshc.gz
• Moon_LOLA_shape_pa_1439.bshc.gz
• Moon_LOLA_shape_pa_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.

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.