Astrogeology Science Center

Shape models fit to a spherical harmonic expansion of degree 6 (Zebker et al., 2009)
Shape models fit to a spherical harmonic expansion of degree 6 (Zebker et al., 2009)
Polar color-coded topography maps in stereographic projection (Lorenz et al., 2013)
Polar color-coded topography maps in stereographic projection (Lorenz et al., 2013)
Topographic profiles along meridians from the south pole at left to north pole at right (Lorenz et al., 2013)
Topographic profiles along meridians from the south pole at left to north pole at right (Lorenz et al., 2013)

These files are part of the Global Topographic Data Record (GTDR) series of Digital Map Products (DMP) produced by the Cassini RADAR Science Team.  They contain a variety of different models for the global shape of Titan obtained by interpolation or by least-squares fitting to RADAR altimetry and SARTopo data.  Data values in the files (except GTD*) represent the elevation in meters of the model surface relative to a reference sphere with a radius of 2575.0 km.

The interpolated topographic models (GTI*) were produced by Ralph Lorenz, Applied Physics Lab, Johns Hopkins University.  Tensioned spline interpolation was applied in standard and oblique map latitude-longitude coordinates and the results were merged to obtain a continuous model even at the poles.  Data values in the GTD* files indicate the distance from a given point to the nearest topographic data point used in the interpolation.  See Lorenz et al. (2013) for a description of these files.

The least-squares fitted models were produced by Howard Zebker, Stanford University.  Shape models fitted to the data include spherical harmonic expansions (PDF) and a variety of ellipsoids (PDF)  with differing constraints on the number of distinct semiaxes, offsets, and rotations.  See Zebker et al. (2009) for a description of the modeling process, based on an earlier and less extensive collection of elevation data.

All files are version 01, produced in 2012, containing data from Titan flybys TA through T77.  These files will be officially delivered to the PDS as part of the DMP archive in the near future.

Base file names are identical to the PRODUCT_ID, which is a permanent, unique identifier assigned to a data product by the producer, and take the form "aabcdeefggg_Thhh_Vnn"

where:

  • aa - Dataset
    • GT - GTDR
  • b - Kind and data type of data or fit
    • 0 - Spherical harmonic expansion of degree and order 0, equivalent to a sphere with no displacement from the center of mass
    • 1 - Spherical harmonic expansion of degree and order 1
    • 9 - Spherical harmonic expansion of degree and order 9
    • D - Distance (km) from each point in the GTI interpolated model to the nearest topographic data point used.
    • I - Interpolated (tensioned spline) surface through the topographic data
    • S - Sphere with 3 dimensional displacement from the center of mass
    • T - Triaxial ellipsoid with 3 angles of rotation and 3 dimensional displacement from the center of mass
    • U - Triaxial ellipsoid with 3 dimensional displacement but no rotations
    • V - Triaxial ellipsoid with no rotation or displacement
    • X - Biaxial ellipsoid (spheroid) with 2 angles of rotation and 3 dimensional displacement from the center of mass
    • Y - Biaxial ellipsoid with 3 dimensional displacement but no rotations
    • Z - Biaxial ellipsoid with no rotation or displacement
  • c - Map projection
    • E - Equirectangular Cylindrical
  • d - Map resolution
    • B - 2 pixels/degree
    • D - 8 pixels/degree
  • ee - Absolute value of latitude at center of file, rounded to nearest degree
  • f - Hemisphere of center of file
    • N - North
    • S - South
  • ggg - West longitude at center of file, rounded to nearest degree
  • Thhh - Index of Titan flyby from which data are included.  T is a literal character indicating this is the flyby, and hhh is a  three-digit integer giving the flyby number; for flyby Ta, the value 00A is used.  Note that for the GRDR, GSDR, and MIDR, the index of the highest-numbered flyby included in the product is given.
  • Vnn - Version number of product.  V is a literal character indicating this is the version, and nn is a two-digit integer.

File extensions indicate the type of file:

  • *.IMG.gz - PDS raster image file with embedded label, compressed with the gzip protocol
  • *.LBL - Detached copy of the PDS label pointing to the image data in the .IMG file, provided to allow users to obtain information about the file before compressing it.
  • *.LAB - Detached ISIS 2 cube label pointing to the image data in the .IMG file, provided to allow opening of the image in ISIS without pds2isis translation.

References

  • Lorenz, R.D., Stiles, B.W., Aharonson, O., Lucas, A., Hayes, A.G., Kirk, R.L., Zebker, H.A., Turtle, E.P., Neish, C.D., Stofan, E.R., Barnes, J.W.,and the Cassini RADAR Team, 2013, A global topographic map of Titan, Icarus, 225, 367–377, doi: 10.1016/j.icarus.2013.04.002.
  • Zebker, H.A., Stiles, B.W., Hensley, S., Lorenz, R.D., Kirk, R.L., and Lunine, J.I., 2009, Size and shape of Saturn's moon Titan, Science, 324, 921–923, doi:10.1126/science.1168905.