Data Set Overview  :   A global map of the abundance of hydrogen (micrograms/g) within the  regolith of asteroid 4 Vesta is provided as an ASCII table. The map  data are given for half-degree, equal-angle pixels.   The data reduction and analysis methods are presented in  PRETTYMANETAL2012. Epithermal counting rates measured in Dawn's  circular, polar, low-altitude mapping orbit (LAMO), at a mean distance  of about 210 km from Vesta's surface were corrected for variations  in the flux of galactic cosmic rays (GCR) and solid angle. The data were  acquired in early LAMO (Time-interval IA, described in  the Supplementary Information of PRETTYMANETAL2012, Fig.1 and Table 2).  during a long period (30 days) of continuous instrument operation and  steady GCR counting rates. The corrected epithermal counting data were  globally mapped on 15-deg equal-area pixels, smoothed using tesseral  spherical harmonics and rebinned onto a two degree cylindrical map.  Hydrogen abundance was determined from the smoothed epithermal map  using Eq. 1 of PRETTYMANETAL2012.   Parameters  :   Each row of the table provides the abundance of hydrogen for a  single rectangular pixel. The format for each row is  '(i10,6(f7.1),f8.2)'. East longitude convention is used (-180 to 180  degrees). The longitudes are given in the Claudia Double Prime coordinate system (see Confidence Level Note). Each pixel spans a separate and  unique portion of Vesta's surface, and together, the pixels provide full  global coverage. The BROWSE directory displays the data as a global map.  The column descriptions follow:   COLUMN NAME FORMAT DESCRIPTION UNITS  0 PIXEL_INDEX (I10) N/A  1 MIN_LAT (F7.1) Pixel latitude lower boundary deg  2 MAX_LAT (F7.1) Pixel latitude upper boundary deg  3 DELTA_LAT (F7.1) Width of the pixel in latitude deg  4 MIN_LON (F7.1) Pixel longitude lower boundary deg  5 MAX_LON (F7.1) Pixel longitude upper boundary deg  6 DELTA_LON (F7.1) Width of the pixel in longitude deg  6 H_ABUND (F8.1) Hydrogen abundance micrograms/g

Confidence Level Overview  :   The data set is a high order data product derived from epithermal neutron  counting data acquired by GRaND in LAMO as described by PRETTYMANETAL2012.   Review  :   This data set is in review by NASA Planetary Data System.   Data Coverage and Quality  :   The data set contains a global map of the abundance of hydrogen within  Vesta's regolith. There are no gaps in coverage. The depth sampled  by epithermal neutrons from which hydrogen abundances are provided is a  few decimeters (for example, see PRETTYMANETAL2011).   Coordinate System:   The data were analyzed and mapped in the Claudia coordinate system, in which the prime meridian passes close to a small crater named Claudia. In this  coordinate system, the prominent Marcia crater is located at 190E longitude. Maps published by the Dawn Geochemistry Working Group in the literature are  presented in the Claudia coordinate system [PRETTYANETAL2012,  LAWRENCEETAL2013, PEPLOWSKIETAL2013, PRETTYMANETAL2013, YAMASHITAETAL2013].   Consistent with IAU guidelines, maps of GRaND data in this archive are  presented in the 'Claudia Double Prime' (CDP) coordinate system. CDP  has the same pole position as Claudia such that latitudes are the same;  however, the prime meridian of CDP is shifted by 210 degrees from that of  Claudia, passing 20 degrees to the east of Marcia. The coordinate systems  are describes in detail by J.-Y. Li in VESTA_COORDINATES_120918.pdf, which  accompanies this archive in the DOCUMENTS directory.   All of the maps use rectangular pixels with east longitudes within  -180 to 180 degrees in the Claudia system. For archiving, the longitudes  were converted to CDP as follows:   longitude_CDP : longitude_Claudia - 210 degrees. If longitude_CDP is  less than -180 degrees, add 360 degrees.   For example, if longitude_Claudia : -170 (the location of Marcia crater),  then longitude_CDP : -20.   Similarly, longitudes in the CDP system can be converted to Claudia as  follows:   longitude_Claudia : longitude_CDP + 210. If longitude_Claudia is greater  than 180 degrees, subtract 360 degrees.   Thus, the pixel longitude boundaries, which were tabulated in this archive  in the CDP system, can easily be converted back to the Claudia system, in  which the data were analyzed, by the user when desired. To further  facilitate comparison between the PDS archived maps and those published in  the literature, a 'side-by-side' display of each map in the Claudia and  CDP systems is included in the accompanying browse file (see BROWSE  directory).   For further clarification, we note that map pixels in the Claudia system  always have MIN_LON < MAX_LON; however, when transformed into the  CDP system, not all pixels will meet this condition. For example, in  some quasi-equal area maps, the polar pixels have MIN_LON : -180 and  MAX_LON : 180 in the Claudia coordinate system. These pixels span  360 degrees in longitude. When transformed to the CDP coordinate system,  these pixels have MIN_LON : -30 and MAX_LON : -30, such that MIN_LON :  MAX_LON. In addition, for some maps, a portion of the pixels will have  MIN_LON > MAX_LON when transformed into the CDP system. To avoid confusion, we included the width of each pixel in longitude as DELTA_LON. For example, for the aforementioned polar pixels, DELTA_LON : 360.   Limitations  :   Assumptions and limitations underlying the analysis of hydrogen abundances  within Vesta's regolith are described by PRETTYMANETAL2012. We note  that the tabulated values give the range of hydrogen abundances on Vesta,  with a minimum of 0 micrograms/g and a maximum of about 400 micrograms/g.  The map gives the absolute variation in hydrogen abundance, assuming that  the minimum abundance of hydrogen is 0 micrograms/g at a location where  maximum corrected epithermal neutron counting rates are observed (within  Rheasilvia basin). If the minimum abundance of hydrogen on Vesta were  known, then the map would be properly adjusted by adding this value to each  pixel.   Because the epithermal counting data were smoothed prior to calculating  the hydrogen abundance (Eq. 1 of PRETTYMANETAL2012), the mapped data have  high precision. Thus, statistical uncertainties are not reported.  Systematic errors in hydrogen abundance are expected to be on the order  of 50 micrograms/g, as indicated by PRETTYMANETAL2012.