NASA Logo, National Aeronautics and Space Administration
NASA Space Science Data Coordinated Archive Header

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

NSSDCA ID: PSSB-00706

Availability: Archived at NSSDC, accessible from elsewhere

Description

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

Dataset overview

This data set contains a Ceres regional (Occator) digital terrain model based on the Dawn Low Altitude Mapping orbit (LAMO) Framing Camera 2 (FC2) images and derived by using the stereo photo-grametric (SPG) method. The LAMO DTM covers only the region around the Occator crater. The DTM has a lateral spacing of 32 m/pixel (256 pixel/degree) and a vertical accuracy of about 1.5 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. During the LAMO mapping phase, it is not possible to map the entire body at enough different viewing geometries to produce a global SPG DTM at high resolution. At LAMO, the entire illuminated surface was mapped in the clear filter at nadir (pointed towards Ceres center). This single map required nearly four months to acquire. Once the surface was fully mapped at nadir, an off-nadir mapping campaign was begun in order to support topographic analysis. While a large fraction of the surface was mapped at three or more stereo angles, the combination of the huge number of images required and gaps in coverage make the creation of a global LAMO DTM unachievable at this time. Several selected targets of interest were identified in the data acquired at higher altitudes (Ahuna Mons, Occator, Haulani, and Oxo craters) so special effort was put into acquiring multiple views of these features. Thus far, only Occator has been fully analysed to produce a regional DTM. This data set may be updated in the future to include additional regional DTMs if time and resources are available. 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 LAMO 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 ==================================================================== region around the Occator crater. In total, about 550 images were selected for the analysis. 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, multi-image matching processes at full image resolution were carried out to yield ~1.8 billion surface points with a calculated mean intersection error of +/- 2.8 m resulting in ~1.5 m height accuracy. A list of the raw FC2 images (CERES-CON-LA2C2E-IMAGE-LIST.TXT) used by the sftware to produce the Occator regional DTM has been included in the DOCUMENT directory of this archive volume.

Data Products

All of the archive data files are found in the DATA directory of the PDS archive volume DWNCLSPC_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. At present, there is only a single data (browse, tiff) file in this dataset. Name Content -------------------------------------------------------------CE_LAMO_L_OCCATOR_EQU_DTM. Occator DTM, equidist cylindrical 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. The Occator DTM is centered at 19.5 degrees north latitude, 239.5 degrees east longitude (Ceres body-fixed coordinates [PREUSKERETAL2016]) and covers 33 degrees of latitude and longitude.

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/DWNCLSPG_2/

Alternate Names

  • DAWN-A-FC2-5-CERESLAMODTMSPG-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
Dr. Frank PreuskerGeneral Contactfrank.preusker@dlr.de
[USA.gov] NASA Logo - nasa.gov