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.