Spherical harmonic models of the shape of Enceladus [JPL SPC]

This archive contains two spherical harmonic models of the shape of Saturn's moon Enceladus, truncated at different maximum spherical harmonic degrees. The highest resolution model has a maximum spherical harmonic degree of 1023, which was generated from an ICQ shape model with Q=1024.

The data used to generate these models are from a JPL stereo photoclinometric shape model based on images obtained by the Cassini mission, as found in the file cas_enceladus_ssd_spc_1024icq_v1.bds on NASA's PDS website. The vertices were first converted from Cartesian to spherical coordinates, from which a regular gridline registered netcdf file was created using the generic-mapping-tools function surface with a tension of 0.6 and with a grid spacing of 0.087890625 degrees. This file was then 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 two files in this archive are

• Enceladus_JPL_SPC_shape_1023.bshc.gz
• Enceladus_JPL_SPC_shape_719.bshc.gz

The numbers 1023 and 719 in the filename refer to the maximum spherical harmonic degree of file, which corresponds to effective spatial resolutions of ~11.4 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 model was generated by truncating the spherical harmonic coefficients of the highest resolution model.