Data Set Information
DATA_SET_TERSE_DESCRIPTION Dawn Framing Camera 2 Ceres HAMO global digital terrain model created by using the stereo-photogrametric method.
Dataset overview
      This data set contains the Ceres digital terrain model (DTM) based on
      the Dawn High Altitude Mapping orbit (HAMO) Framing Camera 2 (FC2)
      imagesand derived by using the stereo photogrammetry (SPG) method. The
      HAMO DTM covers approximately 98% of the Ceres surface (few permanently
      shadowed areas near the poles required interpolation). The a DTM has
      a lateral spacing of ~136.7 m/pixel (60.0 pixel/degree) and a vertical
      accuracy of about 10 m.

      Dawn mission is equipped with two identical framing cameras (FC1 & FC2)
      [SIERKSETAL2011] which have one clear filter and seven band pass
      filters. At Ceres, only the FC2 was used to acquire science images
      while the FC1 was held in reserve. Clear filter images which were
      taken during HAMO were used to produce a global DTM of the
      illuminated part of Ceres [PREUSKERETAL2016]. Dawn orbited Ceres
      during in 6 cycles between August 16 and October 23, 2015 at the
      HAMO altitude of ~1475 km. A cycle is a single complete mapping of
      surface at a fixed attitude (nadir or off-nadir). The framing camera
      acquired about 2350 clear filter images [PREUSKERETAL2016] during the
      HAMO phase. The images were taken with different viewing angles and
      similar illumination conditions by slewing the spacecraft to various
      off-nadir attitudes. These images are analyzed by using the SPG method
      [PREUSKERETAL2011, RAYMONDETAL2011] to produce the Ceres HAMO DTM.

      For more information on the contents and organization of the volume
      set refer to the AAREADME.TXT file located in the root directory of
      the data volumes.  A description of the map projections used in this
      data sets is provided in the file in the catalog directory
      of this archive volume.

      The stereo-photogrammetric processing of Ceres images is based on a
      software suite that has been developed at the German Aerospace Center
      (DLR BERLIN-ADLERSHOF) within the last decade. It has been applied to
      several planetary image data sets and covers the entire workflow
      from photogrammetric block adjustment to digital terrain model (DTM)
      and map generation [PREUSKERETAL2016]. Details of the SPG data
      processing pipeline can be found in [RAYMONDETAL2011] or
      [PREUSKERETAL2011]. However, for those who do not have easy access to
      those texts, a STEREO_PHOTOGRAMMETRY document derived from those papers
      is included in the DOCUMENTS directory of this archive volume.

      All HAMO clear filter images were constrained by stereo requirements
      (Table 1) and achieved at least triple stereo image coverage for the

                  Table 1    Requirements for stereo processing
           Differences in illumination           <10 degrees
           Stereo angle                        15-55 degrees
           Incidence angle                     10-90 degrees
           Emission angle                       0-55 degrees
           Phase angle                        10-180 degrees

      entire illuminated surface. In total, about 10,000 independent
      multi-stereo image combinations were used to determine selected
      image tie points by multi-image matching for the set-up of a
      three-dimensional (3D) control network of ~30,000 surface points.
      The control point network defines the input for the photogrammetric
      least squares adjustment where corrections for the nominal orientation
      data (pointing and position) are derived. The 3D point accuracy of the
      resulting ground points have been improved from +/-200 m to
      +/-16 m (0.12 pixel). The Ceres spin axis orientation, formerly
      determined from Dawn Survey observations [CERES_COORD_SYS_151014,
      this volume], to: right ascension = 291.431 +/- 0.01 (degrees),
      declination = 66.761 +/- 0.01 (degrees). The Ceres spin rate has also
      been updated from the Earth-based observations [CHAMBERLAINET2009] to
      W1 = 952.15323 +/- 0.00005 degrees per day. Finally, the value of W0
      was changed to 170.488 +/- 0.01 (degrees) so that the IAU approved
      tiny crater 'Kait' (PREUSKERETAL2016, Figure 1) remains located at
      zero longitude [ROATSCHETAL2016].  All updates to the IAU 2015
      parameters are within the stated error limits of those parameters and
      have equal or lower error estimates.

           Table 2    Differences from IAU 2015 values for Ceres
                       IAU 2014               Pruesker et al. 2016
      Right Ascension   291.418 +/- 0.03        291.431 +/- 0.01     degrees
      Declination        66.764 +/- 0.03         66.761 +/- 0.01     degrees
      W1               952.1532 +/- 0.00003   952.15323 +/- 0.00002* deg/day
      W0               170.650                  170.488 +/- 0.01     degrees
      * One sigma error estimate, F. Preusker, personal communication

      Finally, 10,000 individual multi-image matching processes at full
      image resolution were carried out to yield ~2.8 billion object points.
      The achieved mean forward ray intersection accuracy of the ground
      points is +/- 16 m. Based on the HAMO DTM, the Ceres shape is best-fit
      with a triaxial ellipsoid (482.8, 480.6, 445.0 km) with its long
      axis at 45.9 degrees east.

    Data Products
      All of the archive data files are found in the DATA directory of
      the PDS archive volume DWNCHCSPC_2. Data are stored in PDS image
      format (.IMG) with attached PDS3 labels. In addition to the archive
      DTM, browse versions are provided in JPEG format (.JPG) in the
      BROWSE directory and in TIFF format (.TIF)in the EXTRAS directory.

      Name                        Content
      CE_HAMO_G_00N_180E_EQU_DTM  Global DTM, equidist cylindrical projection
      CE_HAMO_G_90N_000E_STE_DTM  North polar stereographic projection
      CE_HAMO_G_90S_000E_STE_DTM  South polar stereographic projection.

      All of the Ceres SPG DTM products have a SCALING_FACTOR of 1.0  and
      and OFFSET of 470000 m (as noted in the PDS product labels). Conversion
      from Digital Number to HEIGHT, i.e. elevation in meters, is:
           HEIGHT = (DN * SCALING_FACTOR).
      The conversion from Digital Number to PLANETARY_RADIUS in meters is:
      where OFFSET is the radius of the reference sphere.

    Ancillary Products
      The DTM archived here is inconsistent with the IAU (2015) approved
      Ceres coordinate system that is based on Dawn Ceres Approach and
      Survey images (described above). SPICE users of these HAMO SPG
      DTM products will require a specific SPICE PCK file containing
      the planetary constants described above (dawn_ceres_SPG20160107.tpc).
      This file can be found in the GEOMETRY directory on this archive volume.
      Modeling of the shape of Ceres is an ongoing process. Dawn has acquired
      much higher resolution images of Ceres from its Low Altitude Mapping
      Orbit (LAMO) that can be used for stereo photogrammetric analysis in
      the near future. Those images were still being acquired at the time
      that this document was written. The Dawn mission does not anticipate
      petitioning the IAU to consider updating the current Ceres coordinate
      system definition until the high resolution images can be analyzed.
      This DTM and the associated coordinate system update are preliminary
      products created at the end of the Dawn prime mission as contractually
      required. These products will be updated after the end of the extended
      mission at low altitude.
DATA_SET_RELEASE_DATE 2016-09-01T00:00:00.000Z
START_TIME 2015-08-16T12:00:00.000Z
STOP_TIME 2015-10-23T12:00:00.000Z
MISSION_START_DATE 2007-09-27T12:00:00.000Z
MISSION_STOP_DATE 2017-06-30T12:00:00.000Z
NODE_NAME Small Bodies
Data Coverage
      The HAMO SPG DTM covers approximately 98% of the Ceres surface (few
      permanently shadowed areas near the poles required interpolation)
      with a height accuracy of 10m.
CITATION_DESCRIPTION Roatsch,T., E. Kersten,K.-D. Matz,F. Preusker, F. Scholten, S. Elgner, S.E. Schroeder, R. Jaumann, C.A. Raymond, C.T. Russell, DAWN FC2 DERIVED CERES HAMO DTM SPG V1.0, DAWN-A-FC2-5-CERESHAMODTMSPG-V1.0, NASA Planetary Data System, 2016.
ABSTRACT_TEXT Abstract ======== This data set contains the Ceres digital terrain model based on the Dawn High Altitude Mapping orbit (HAMO) Framing Camera 2 (FC2) images and derived by using the stereo photo-grametric (SPG) method. The HAMO DTM covers approximately 98% of the Ceres surface (few permanently shadowed areas near the poles required interpolation). The a DTM has a lateral spacing of ~136.7 m/pixel (60 pixel/degree) and a vertical accuracy of about 10 m.