Dataset overview : This accumulating data set includes Ceres global mosaics and quadrangles derived from images acquired by the Framing Camera 2 (FC2) on the NASA Dawn spacecraft. Global mosaics are provided in cylindrical and polar stereographic projections. The quadrangle mosaics use Mercator (equatorial), Lambert conformal (mid-latitude) and stereographic projections. Clear and color mosaics are provided for high altitude mapping orbit (HAMO) and clear filter mosaics only in the low altitude mapping orbit (LAMO) science phases. Dawn mission is equipped with two identical framing cameras (FC1 & FC2) [SIERKSETAL2011] which have one clear filter and seven band pass filters. At Ceres, 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 Ceres with a resolution of ~140m/pixel [ROATSCHETAL2016]. Dawn orbited Ceres during in 6 cycles between August 16 and October 23, 2015 at the HAMO altitude of ~1475 km. A cycle is a single complete mapping of surface at a fixed attitude (nadir or off-nadir). The framing camera acquired about 2490 clear filter images [ROATSCHETAL2016] during the HAMO phase. Images were acquired with different viewing angles and illumination conditions in order to provide input to the stereo- photogrametric [PREUSKERETAL2016] and stereo-photoclinometric analysis of the Ceres topography. DWNCHCFC2_2 contains mosaics built using 386 images from HAMO cycle 1 with minor gaps filled with images from cycle 2. Color images were acquired during HAMO in Cycles 1 (nadir) and 5 (near nadir). Due to data storage and downlink limitations, only three of the seven filters were acquired pole-to-pole in the color imaging cycles. The remaining 4 filters were acquired in only the best illuminated regions between +/- 70 deg latitude in Cycle 1 and from the north pole to 70 deg South in Cycle 5. Cycle 1 pole-to-pole filters were filters 2 (555 nm), 3 (749 nm), and 7 (653 nm) and Cycle 5 acquired filters 2, 3, and 5 (965 nm). Color filter mosaics are archived on volume DWNCHFFC2_2. In general, the mosaics were created by using images from Cycle 1 with gaps filled by using images from Cycle 5. This volume includes both individual filter mosaics as well as Clementine color ratio mosaics. In LAMO (low altitude mapping orbit), only clear filter images were acquired for the the first ~4 nadir mapping cycles. Later in LAMO, clear filter images were acquired at various off-nadir angles. Color imaging was limited to a few selected targets during off-nadir cycles because of data storage, downlink, and image smear limitations. At low Ceres altitude the combination of long exposures times and rapid Dawn motion relative to Ceres made smearing a significant concern for the various color filters while the clear filter smear was sub-pixel. No global or quadrangle mosaics can be created from the limited number of LAMO color images. LAMO clear filter mosaics can be found on the DWNCHCFC2_2 archive volume. 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 [SCHROEDERETAL2013A, SCHROEDERETAL2014]. The next step towards the cartographic products is to ortho-rectify the images to the proper scale and map projection type. This process requires detailed information of the Dawn orbit and attitude data and of the topography of the targets. Both improved orientation and a high-resolution shape model are provided by stereo processing (bundle block adjustment) of the HAMO stereo image dataset [PREUSKERETAL2016], Ceres' shape model is used for the calculation of the ray intersection points, while the map projection itself is placed onto a reference sphere of Ceres with a mean radius of 470 km. The phase angle changed from about 10 degrees near the equator to 90 degrees at the poles. The mean brightness value of each point for every phase angle was derived and used to calculate a phase angle dependent brightness function. This function was applied to all images to minimize the brightness changes between the images at different latitudes. The final step was the mosaicking of all images to a global mosaic of Ceres, the so-called basemap. The longitude system of Ceres is defined by the tiny crater Kait [ROATSCHETAL2016], the pole axis and the rotation rate were calculated during the bundle block adjustment [PREUSKERETAL2016]. The Dawn team proposed 81 names for geological features. By international agreement, craters must be named after gods and goddesses of agriculture and vegetation from world mythology, whereas other geological features must be named after agricultural festivals of the world. The nomenclature proposed by the Dawn team was approved by the IAU [http://planetarynames.wr.usgs.gov/]. For more detailed information on the image calibration process, please refer to [SCHROEDERETAL2013A] and [SCHROEDERETAL2014]. DWNCHCFC2_2 Data Products : The Ceres HAMO atlas consists of 15 map tiles with a resolution of ~140 m/pixel. The tiling scheme conforms to those proposed by Greeley and Batson [GREELEY&BASTON1990] for medium-sized planetary bodies and high-resolution imaging. A map scale of about 1:750,000 guarantees a mapping at the highest available Dawn FC HAMO resolution and results in an acceptable printing scale for the hardcopy map of 5 pixel/mm. The individual tiles were extracted from the global mosaic and reprojected, coordinate grids were superposed as graphic vectors and the resulting composites were converted to the common PDF-format. The equatorial part of the map (22S to 22N latitude) is in Mercator projection onto a secant cylinder using standard parallels at 13S and 13N latitude. The regions between the equator region and the poles (66S to 21S and 21N to 66N latitude) are in Lambert's conic conformal projection with two standard parallels at 30N and 58N (or 30S and 58S, respectively). The poles are in stereographic projection (90S to 65S latitude and 65N to 90N latitude). Individual tiles overlap in the North-South direction by one degree, however no overlapping region is present in the East-West direction. The map tiles have a true scale of 1:750,000 at the standard parallels and have the same scaling factors in the overlapping regions at the matching parallels +/-21.34 deg and +/-65.19 deg latitude, 1.0461 and 1.0484 respectively [SNYDER1987]. The longitudinal extension of the map tiles are for those in Mercator projection 72 deg, for those in Lambert's projection 90 deg, and for the polar caps 360 deg. Using this tiling scheme for Ceres with a high-resolution mosaic, the printed map tiles have a size of 125 cm in width by 90 cm in height. All of the archive data files are found in the DATA directory of the PDS archive volume DWNCHCFC2_2. Data are stored in PDS image format (.IMG) with attached PDS3 labels. In addition to the archive mosaics, browse versions are provided in JPEG format (.JPG) in the BROWSE directory and in TIFF format (.TIF)in the EXTRAS directory. Name Content -------------------------------------------------------------- CE_HAMO_G_00N_180E_EQU_CLR Global mosaic, equidist cylindrical proj. CE_HAMO_G_90N_000E_STE_CLR North polar stereographic proj. CE_HAMO_G_90S_000E_STE_CLR South polar stereographic proj. CE_HAMO_Q_00N_036E_MER_CLR Haulani quadrangle, Mercator proj. CE_HAMO_Q_00N_108E_MER_CLR Kerwan quadrangle, Mercator proj. CE_HAMO_Q_00N_180E_MER_CLR Nawish quadrangle, Mercator proj. CE_HAMO_Q_00N_252E_MER_CLR Occator quadrangle, Mercator proj. CE_HAMO_Q_00N_324E_MER_CLR Rongo quadrangle, Mercator proj. CE_HAMO_Q_43N_045E_LAM_CLR Coniraya quadrangle, Lambert proj. CE_HAMO_Q_43N_135E_LAM_CLR Dantu quadrangle, Lambert proj. CE_HAMO_Q_43N_225E_LAM_CLR Ezinu quadrangle, Lambert proj. CE_HAMO_Q_43N_315E_LAM_CLR Fejokoo quadrangle, Lambert proj. CE_HAMO_Q_43S_045E_LAM_CLR Sintana quadrangle, Lambert proj. CE_HAMO_Q_43S_135E_LAM_CLR Toharu quadrangle, Lambert proj. CE_HAMO_Q_43S_225E_LAM_CLR Urvara quadrangle, Lambert proj. CE_HAMO_Q_43S_315E_LAM_CLR Yalode quadrangle, Lambert proj. CE_HAMO_Q_90N_000E_STE_CLR Asari quadrangle, stereographic proj. CE_HAMO_Q_90S_000E_STE_CLR Zadeni quadrangle, stereographic proj. DWNCHFFC2_2 Data Products : All of the archive data files are found in subdirectories of the DATA directory of the PDS archive volume DWNCHFC2_2. The DATA directory is split into GLOBAL and XXXX_QUAD directories where XXXX is the quadrangle name. Data are stored in PDS image format (.IMG) with attached PDS3 labels. In addition to the archive mosaics, browse versions are provided in JPEG format (.JPG) in the BROWSE directory and in TIFF format (.TIF)in the EXTRAS directory. Both BROWSE and EXTRAS mimic the DATA directory structure and contents. Given the large number of files on this volume, a naming convention is provided rather than a file listing. File Naming Convention: CE_HAMO_M_LATx_LONx_PRO_FILTx.IMG CE_HAMO is literal, Ceres HAMO; T is the mosaic type where G : global, Q : quadrangle; LATx is the center latitude of the mosaic; LONx is the center longitude of the mosaic; PRO is the projection identifier: EQU is equidistant cylindrical projection, STE is stereographic projection, MER is Mercator projection, and LAM is Lambert conformal projection; FILTx is either the filter identifier (FILT2 : F2) or CLEM for the Clementine color ratio 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 : ~140 m/pixel Calibration, stray light correction, and photometric correction as described by [SCHROEDERETAL2013A] and [SCHROEDERETAL2014]. DWNCLCFC2_2 Data Products : The LAMO atlas uses the same tiling scheme as the HAMO atlas described above. The map resolution is about ~35 m/pixel. A map scale of about 1:200,000 (TBR) guarantees a mapping at the highest available Dawn FC LAMO resolution. All of the LAMO clear filter archive data files are found in the DATA directory of the PDS archive volume DWNCHCFC2_2. Data are stored in PDS image format (.IMG) with attached PDS3 labels. In addition to the archive mosaics, browse versions are provided in JPEG format (.JPG) in the BROWSE directory and in TIFF format (.TIF)in the EXTRAS directory. The structure of and file naming on this volume is effectively identical to the HAMO volume with the HAMO replaced by LAMO in the names.

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 Ceres although the percent coverage is quite high with many products exceeding 98%. The extreme south pole was missed as a result of a lack of illumination. As previously described, not all of the color filters were acquired pole-to-pole. See [POLANSKEYETAL2016] for more information regarding the in-flight performance of the planned science activities at Ceres.