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

DAWN FC2 DERIVED VESTA GLOBAL MOSAICS V1.0 (PDS)

NSSDCA ID: PSSB-00619

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 includes various Vesta global mosaics derived from images acquired by the Framing Camera 2 (FC2) on the NASA Dawn spacecraft at the high and low altitude mapping orbits (HAMO and LAMO). Data are provided in cylindrical and polar stereographic projections. In addition to the mosaics, the flatfield and stray light correction images used during the processing of the raw images are provided. 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. Clear filter images which were taken during HAMO were used to produce a global mosaic of the illuminated part of Vesta with a resolution of ~60m/pixel [ROATSCHETAL2012]. Dawn orbited Vesta during in 6 cycles between the end of September and early November 2011 (HAMO-1) and another 6 cycles between late June and the end of July in 2012 (HAMO-2). A cycle is a single complete mapping of surface at a fixed off-nadir attitude. The framing camera took about 2500 clear filter images with a resolution of about 60 m/pixel during each of these mapping phases. The images were taken with different viewing angles and illumination conditions in order to provide input to the stereo-photogrametric [PREUSKERETAL2012] and stereo-photoclinometric analyses of the Vesta topography. Images from one cycle (HAMO-1, cycle #3; HAMO-2, cycle 6) were selected for the mosaicking process to have similar viewing and illumination conditions. HAMO-1, cycle #3 with 518 images and HAMO-2, cycle 3 with 440 images were selected since each was the first cycle with nearly complete global coverage. Very minor gaps in the coverage were filled with three images from HAMO-1, cycle #4. HAMO-1 occurred during the northern winter and HAMO-2 occurred during the northern spring so the southern hemisphere was mosaicked using HAMO-1 images and the northern hemisphere used images acquired during HAMO-2. Full color imaging (clear plus seven band pass filters) was performed twice during HAMO-1 (cycles 1 and 6) with body-center pointing. These images were used to produce the southern hemisphere portions of the various color and color ratio mosaics included with this data set. Since most of the surface of Vesta south of 30 degrees north was already imaged in full color during HAMO-1, color images were only acquired during the final cycle of HAMO-2 (cycle 6) when the northern hemisphere had its maximum illumination. Even still, the illumination was poor at the highest latitudes. Color images from HAMO-2, cycle 6 were used to create the northern hemisphere color image mosaics. Imaging in LAMO was challenging for several reasons: large gravity gradient influences on the spacecraft trajectory, and low downlink bandwidth for image return. The FC2 acquired about 10,000 clear filter images in LAMO allowing the creation of a global mosaic of Vesta with a resolution of 20m/pixel. This LAMO atlas is a higher-resolution supplementary atlas to the HAMO atlas [ROATSCHETAL2012]. The LAMO mission phase occurred during Northern winter which kept the north pole region in darkness; only 84% of the surface was illuminated and good illumination(incidence angle less than 70 deg) was only available for 66.8% of the surface [ROATSCHETAL2013]. 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 image data returned from the spacecraft are distributed inside the Dawn team in PDS (Planetary Data System) format [http://pds.jpl.nasa.gov]. The first step of the image processing pipeline is the conversion to VICAR (Video Image Communication and Retrieval) format [http://rushmore.jpl.nasa.gov/vicar.html] followed by the radiometric calibration of the images. The next step of the processing chain deals with the orthorectification of the images into a cartographic map projection at a specified scale. This process requires detailed information with regard to Vesta's global shape. Vesta is best described by a global digital terrain model as derived from FC images by [PREUSKERETAL2012] and [JAUMANNETAL2012]. However, to facilitate comparison and interpretation of the maps, the DTM was used only for the calculation of the surface intersection points of the line of sight vectors, while the map projection itself was done onto a sphere with the mean radius (255 km). The Dawn orbit and attitude data used for the calculation of the surface intersection points are provided as SPICE kernels [http://naif.jpl.nasa.gov] and were improved using a bundle-adjustment technique [PREUSKERETAL2012]. A cylindrical equidistant map projection was chosen for the global mosaic. The coordinate system adopted by the Dawn mission for satellite mapping is the IAU ''planetographic'' system, consisting of planetographic latitude and positive east longitude [ARCHINAL2013]. But because a spherical reference surface is used for map projections of the satellites, planetographic and planetocentric latitudes are numerically equal. In addition, stereographic projections of the HAMO and LAMO data are provided for both hemispheres (0-90 deg). The stereographic projections reduce the distortion that is clear in the higher latitude regions of the cylindrical projection. The longitude system of Vesta is defined by the tiny crater Claudia which is located at 206 degrees east (Claudia double-prime coordinates). Mosaicking of the single images was the final step of the image processing. For more detailed information on the image calibration process, please refer to [SCHROEDERETAL2013A],[SCHROEDERETAL2013B] and [SCHROEDERETAL2014]. 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].

Data Products

HAMO Clementine Color Ratio Mosaics

Spectral differences of surface materials are often mapped by using the ratios of various spectral bands to bring out diagnostic spectral features. In this data set we include a global cylindrical projection plus northern and southern hemisphere stereographic projections of of the three color ratios as three bands in the image. The bands are created from the quotients of photometrically corrected color images where: red = filter # 3 / filter # 8 green = filter # 3 / filter # 4 blue = filter # 8 / filter # 3 filter # 3: 749 nm filter # 4: 917 nm filter # 8: 438 nm conversion from real to byte: red : input range 1.106 - 1.337 -> output range 1 - 255 green : input range 1.018 - 2.036 -> output range 1 - 255 blue : input range 0.769 - 0.905 -> output range 1 - 255 map_scale = 60 m/pixel Calibration, stray light correction, and photometric correction as described by [SCHROEDERETAL2013A] and [SCHROEDERETAL2014].

HAMO Color Mosaics

Photometrically and stray light corrected color images from each of the seven band pass filters are mosaicked. The first number in file name is filter number. The map_scale = 60 m/pixel. Calibration, stray light correction, and photometric correction as described by [SCHROEDERETAL2013A] and [SCHROEDERETAL2014].

HAMO Mosaic

Clear filter mosaic with a map scale of 60 m/pixel. Calibration, stray light correction, and photometric correction as described by [SCHROEDERETAL2013A] and [SCHROEDERETAL2014].

LAMO Mosaic

Clear filter mosaic with a map scale of 20 m/pixel. Calibration and photometric correction as described by [SCHROEDERETAL2013A]and [SCHROEDERETAL2014].

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

http://sbn.psi.edu/archive/dawn/fc/DWNVFC2_2/

Alternate Names

  • DAWN-A-FC2-5-MOSAIC-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
[USA.gov] NASA Logo - nasa.gov