Data Set Overview : The Mars Global Surveyor spacecraft included a laser altimeter instrument. The primary objective of the Mars Orbiter Laser Altimeter (MOLA) is to determine globally the topography of Mars at a level suitable for addressing problems in geology and geophysics.  The MOLA Spherical Harmonics Topography Model (SHADR) is a numerical transform of the MOLA Experiment Gridded Data Record (EGDR), a global topography data set. See the MOLA EGDR Software Interface Specification [MOLAEGDRSIS1999] and the PDS Catalog entry for the EGDR data set (MGS-M-MOLA-5-IEGDR-L3-V1.0) for a description of the EGDRs.  The MOLA SHADR follows the general format of Spherical Harmonics ASCII Data Records defined in the SHADR SIS [SIMPSON1999]. The SHADR was defined initially for gravity models derived from Magellan and Mars Observer radio tracking data, but the format has been generalized to be suitable for spherical harmonic expansions of gravity, topography, magnetic, and other fields.  This Mars topography model was produced by Greg Neumann under the direction of David E. Smith, MOLA Principal Investigator.  Further improvements to the model are expected as additional MGS data are incorporated.   Data : The MOLA SHADR is in the form of two ASCII tables, a header table and a coefficients table, contained in a single file with a detached PDS label. The header table consists of a single record of eight data columns that contain descriptive information about the coefficients table. The columns include the assumed gravitational constant, the uncertainty in the constant, the degree and order of the model field, the reference longitude and latitude for the spherical harmonic expansion, and a normalization indicator. A column for the assumed reference radius of the planet is also included for consistency with the general SHADR format, but it is not used or needed for the model.  The EGDR that was the source of the SHADR data set included all MOLA nadir observations from the Orbit Insertion phase, plus Mapping Phase nadir observations from the beginning of mapping through the end of August 1999. Additionally, off-nadir observations of the north pole were included from 87 N latitude and northward, taken during the spring of 1998, and of both poles taken in July of 1999, from 87 N and S to the poles. Orbits 355 and 358 of the Orbit Insertion Phase and parts of orbits 10709 through 10716, inclusive, of the Mapping Phase were excluded because solutions for these orbits were deemed to be poor. (Note: subtract 10000 from a MOLA mapping phase orbit number to determine the equivalent MGS Project orbit number.) Also excluded were shots more than 1 degree off-nadir (except as noted above), channel 4 returns, and any returns not classified as ground returns, e.g., clouds or noise, according to the SHOT_CLASSIFICATION_CODE. A total of approximately 123 million observations are represented in the EGDR.   Parameters : N/A   Processing : See the PDS Catalog entries for the MOLA EGDR and PEDR data sets for a description of the processing applied to the data from which this SHADR is derived.   Ancillary Data : N/A   Coordinate System : The coordinate system is IAU 1991 (Davies et al., Celestial Mechanics and Dynamical Astronomy, 53, 377-397, 1992 [DAVIESETAL1992B]), areocentric, with longitudes measured positive east.   Software : N/A   Media/Format : The MGS MOLA SHADR dataset is available on CD-ROM and electronically via the PDS Geosciences Node web site at http://wwwpds.wustl.edu and the MOLA Science Team web site at http://ltpwww.gsfc.nasa.gov/tharsis/mola.html. Formats are based on standards established by the Planetary Data System (PDS).

See the confidence level notes in the PDS Catalog entries for the MOLA EGDR and PEDR data sets, from which this SHADR is derived.