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 (located at DATA/LAMO_CLEM)  -----------------------------------  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 (located at DATA/LAMO_COLOR)  ------------------  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 (located at DATA/HAMO_CLEAR)  -----------  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 (located at DATA/LAMO_CLEAR)  -----------  Clear filter mosaic with a map scale of 20 m/pixel.  Calibration and photometric correction as described by  [SCHROEDERETAL2013A]and [SCHROEDERETAL2014].

Stray light correction  :  The stray light correction applied to these data [SCHROEDERETAL2014] is a  linear interpolation of the observed pattern which is a simplification  of the true effect. However, the existing data do not support more complex interpolation schemes at this time.   Data Coverage  :  None of the mosaics provide complete surface coverage of Vesta. During  HAMO, some images were lost creating the small gaps in the mid and low  latitude regions. The extreme south pole was missed as a result of  under-sampling and extreme topographic effect and the high northern  latitudes were never fully illuminated. All in all, better than 90%  of the Vesta was imaged at 60m/pixel in the HAMO mission phases.   Clear filter coverage in LAMO is limited to latitudes south of  60 degrees north. In addition, there are a few bands where  images were never acquired. The LAMO orbit was optimized for  gravitational stability rather than imaging coverage. Since there  are only nadir images acquired during LAMO, it was not possible  to create a LAMO resolution DTM. LAMO data were projected on to a  HAMO resolution DTM for photometric correction which reduces the  quality of the correction applied.