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DAWN FC2 DERIVED VESTA DTM SPG V1.0 (PDS)

NSSDCA ID: PSSB-00702

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 Vesta digital terrain model (DTM) based on the Dawn High Altitude Mapping orbit (HAMO) Framing Camera 2 (FC2) image sand derived by using the stereo photogrammetry (SPG) method. The HAMO DTM covers approximately 95% of the Vesta surface (few permanently shadowed areas near the poles required interpolation). The a DTM has a lateral spacing of ~70 m/pixel (64.0 pixel/degree) and a vertical accuracy of +/- 6 m. Dawn mission is equipped with two identical framing cameras (FC1 & FC2) [SIERKSETAL2011] which have one clear filter and seven band pass filters. At Vesta, only the FC2 was used to acquire science images while the FC1 was held in reserve. At Vesta there were two HAMO science phases, both at ~700 km altitude. During the first HAMO (HAMO-1: September 29 - November 1, 2011) Dawn acquired approximately ~2,675 clear filter images with an average image scale of about 63 m/pixel [PREUSKERETAL2011]. At this time, Vesta was in southern summer and most of the northern hemisphere above 35-40 degrees north latitude was poorly illuminated. HAMO-1 consisted of six cycles with the first and last at Vesta center pointing and the other four cycles at various off-nadir angles [POLANSKEYETAL2012]. After completing its low altitude mapping (LAMO) Dawn was allowed to have a second HAMO (HAMO-2) mapping before departing Vesta for Ceres. In HAMO-2 (June 15 - July 24, 2012) Dawn was able to acquire an additional ~2,825 clear filter images with an average image scale of about 65 m/pixel [PREUSKERETAL2014]. HAMO-2 also included six cycles with nadir and off-nadir geometries similar to those used during HAMO-1 [POLANSKEYETAL2012]. HAMO-2 occurred near the Vesta equinox providing much improved lighting conditions in the northern hemisphere. Combining the two data sets, Dawn was able to map nearly 95% of the Vesta surface. All of the HAMO images were used to produce this DTM. All of the various products described below use the same projections. The cylindrical projection covers +/- 90 degrees of latitude and is centered at 30 degrees Claudia double-prime longitude. The minimum and maximum longitudes are -150 and +210 degrees. The northern hemisphere stereographic projection has 90 degrees north latitude at the center and the equator at the edge. The top of projection is 30 degrees Claudia double-prime longitude and the bottom is 210 degrees with longitude increasing to the east. The southern hemisphere projection has 90 degrees south latitude at the center and the equator at the edge, -150 degrees longitude at the top and 30 degrees longitude at the bottom. For a description of the coordinate system, please refer to vesta_coordinates_131018 document contained on this archive volume at the PDS and [ARCHINAL2013]. 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 Vesta 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 5-160 degrees ==================================================================== entire illuminated surface. In total, about 35,000 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 ~83,000 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 +/- 55 m to +/- 8 m (0.15 pixel). The Vesta spin axis orientation, formerly determined from Dawn Survey observations [VESTA_COORDINATES_131018], this volume], to: right ascension = 309.0319 +/- 0.005 (degrees), declination = 42.2228 +/- 0.005 (degrees). The IAU approved tiny crater 'Claudia' remains located at 1.6 deg south latitude and 146.0 degrees east longitude [VESTA_COORDINATES_131018]. All updates to the IAU 2013 parameters are within the stated error limits of those parameters and have equal or lower three sigma error estimates. ===================================================================== Table 2 Differences from IAU 2013 values for Vesta ===================================================================== IAU 2013 Pruesker et al. 2014 --------------------------------------------------------------------Right Ascension 309.031 +/- 0.03 309.0319 +/- 0.005 deg Declination 42.235 +/- 0.03 42.2228 +/- 0.005 deg W1 1617.3329428 1617.3329428 deg/day W0 285.39 285.39 deg ===================================================================== Finally, 35,000 individual multi-image matching processes at full image resolution were carried out to yield ~2.5 billion object points. The achieved mean forward ray intersection accuracy of the ground points is +/- 6 m. Based on the DTM, the Vesta shape is best-fit with a triaxial ellipsoid (285.2, 277.7, 223.8 km) with its long axis at 40.6 degrees east [PREUSKERETAL2014].

Data Products

All of the archive data files are found in the DATA directory of the PDS archive volume DWNVSPC_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 -------------------------------------------------------------VE_HAMO_G_00N_330E_EQU_DTM Global DTM, equidist cylindrical projection VE_HAMO_G_90N_150E_STE_DTM North polar stereographic projection VE_HAMO_G_90S_150E_STE_DTM South polar stereographic projection. All of the Vesta SPG DTM products have a SCALING_FACTOR of 2.0 <m> and and OFFSET of 255000 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 slightly inconsistent with the IAU (2013) approved Vesta coordinate system that is based on Dawn Vesta Survey images (described above). SPICE users of these SPG DTM products will have improved results if they use the SPICE PCK file containing the improved Vesta pole RA and DEC values described above (dawn_vesta_SPG20160901.tpc). This file can be found in the GEOMETRY directory on this archive volume. The difference is sub-pixel when working with HAMO or higher altitude images but can be important when working with LAMO images. Modeling of the shape of Vesta is an ongoing process using both the SPG technique described here and the stereo photoclinometry (SPC) method. The Dawn project will petition the IAU to consider updating the official values for the Vesta pole once the complete description of the results of both methods, their differences, and the reasons for those differences can be published in the peer reviewed literature.

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

https://sbnarchive.psi.edu/pds3/dawn/fc/DWNVSPG_2/

Alternate Names

  • DAWN-A-FC2-5-VESTADTMSPG-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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