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DAWN FC2 DERIVED CERES HAMO DTM SPG V1.0 (PDS)

NSSDCA ID: PSSB-00701

Availability: At NSSDC, Ready for Offline Distribution (or Staging if Digital)

Description

This description was generated automatically using input from the Planetary Data System.

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 dsmap.cat file in the catalog directory of this archive volume.

Processing

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 Preusker 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 <m> 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: PLANETARY_RADIUS = (DN * SCALING_FACTOR) + OFFSET 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.

These data are available on-line from the Planetary Data System (PDS) at:

https://sbnarchive.psi.edu/pds3/dawn/fc/DWNCHSPG_2/

Alternate Names

  • DAWN-A-FC2-5-CERESHAMODTMSPG-V1.0

Discipline

  • Planetary Science: Small Bodies

Additional Information

Spacecraft

Experiments

Questions and comments about this data collection can be directed to: Dr. David R. Williams

 

Personnel

NameRoleOriginal AffiliationE-mail
Dr. Horst Uwe KellerData ProviderMax-Planck-Institut fur Aeronomiekeller@linmpi.mpg.de
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