PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM DATA_SET_ID = "VG1/VG2-S-ISS-2/3/4/6-PROCESSED-V1.0" OBJECT = TEXT PUBLICATION_DATE = 2006-08-15 NOTE = "General overview of the calibrated Voyager image data set from the Saturn encounters." END_OBJECT = TEXT END CALIBRATED VOYAGER IMAGES FROM THE SATURN ENCOUNTERS ---------------------------------------------------- 1. INTRODUCTION This data set contains raw, calibrated and geometrically corrected versions of all the Voyager images from the Saturn encounters. It has been derived from the compressed raw images that were archived previously by the PDS. Images have been processed following standardized procedures using the VICAR software, as provided by the Multi-mission Image Processing Laboratory at JPL. For more information about the processing procedures, see the file DOCUMENTS/PROCESSING.TXT. For details on how to use the images, see DOCUMENTS/TUTORIAL.TXT. This data set is far easier to use than the raw, compressed files and is recommended for essentially all scientific purposes. Scientific users should however, heed the comments about calibration accuracy as found in the aforementioned document. Intermediate steps in the processing are included for any users who might wish to re-calibrate the data themselves. If you reference this data set in a publication, please cite the work of the PDS Rings Node, as follows: Showalter, M.R., M.K. Gordon, and D. Olson, VG1/VG2 SATURN ISS PROCESSED IMAGES V1.0, VGISS_0001-0038, NASA Planetary Data System, 2006. It would also be appropriate to acknowledge the work of the Voyager imaging team, as led by Dr. Brad Smith. 2. VOLUME FORMAT This is a virtual volume, which is too large to fit on current hard storage media such as DVD-ROM. It is currently only available as a directory tree stored on a hard drive. 3. FILE FORMATS 3.1 FILE EXTENSIONS Files on this volume are named according to PDS standards, where the characters after the period indicate the file type. The file types used on this volume are: ASCII text files: PDS detached labels *.LBL ASCII tables and indices *.TAB PDS catalog files *.CAT Text documentation files *.ASC, *.TXT HTML documents *.HTML Binary files Binary images *.IMG Binary data files *.DAT Graphical images for documents *.GIF 3.2 PDS LABELS Every file in this data set is described by an associated PDS label. Most files are described by a detached label, which has the same name as the corresponding file but an extension ".LBL". Most text files (*.TXT, *.CAT) have attached labels. Some pairs of files have the same name but different extensions, e.g. Cxxxxxxx_RESLOC.TAB and .DAT. These files have combined- detached labels, where a single label file Cxxxxxxx_RESLOC.LBL describes both files. See the PDS Standards Reference (JPL D-7669) for a complete description of the PDS label format. This document can also be found on line at http://pds.jpl.nasa.gov/stdref/ 3.3 ASCII TEXT FILES Different popular operating systems use different standards for how ASCII text files are formatted. On Unix systems, lines are terminated by a (linefeed character, control-J, ASCII 10). On Macintosh computers, lines are terminated by a (carriage return character, control-M, ASCII 13). On PCs, lines are terminated by a pair. PDS standards require all text files to use line termination. If the PDS label indicates INTERCHANGE_FORMAT = ASCII or RECORD_TYPE = STREAM, then this line termination is in use. On occasion, users on Unix and Macintosh computers may need to change the line termination on some text files before they can use them. This can be handled via text editors or a variety of utilities. For example, the Unix tr (translate) command can be used to change carriage returns to blanks: tr "\015" " " newfile.txt Some ASCII tables indicate RECORD_TYPE = FIXED_LENGTH and include an additional parameter RECORD_BYTES, which indicates the length in bytes of each record in the file. It should be noted that all ASCII files still include the line terminators, and these two bytes are included in the byte count. For this reason, it is unwise to convert the line terminator to a single character ( on Unix or on Macintosh) because this can change the number of bytes per record and make it incompatible with the label. In these situations, it is recommended that the line terminator be replaced by a space plus or a space plus instead. 3.4 BINARY FILES The binary files on this volume are provided in VICAR format. This is a relatively simple fixed-length file format consisting of an ASCII header followed by consecutive rows of the image as binary integers. See http://www-mipl.jpl.nasa.gov/vicar/vic_file_fmt.html a complete description of the VICAR file format. This information can also be found in DOCUMENTS/VICAR.ASC and DOCUMENTS/VICAR.HTML. Some binary files contain two-byte integers. All two-byte binary integers are in least-significant-byte (LSB) format. This is the native format for Intel-based computers. For computers from Sun and for Macintosh PowerPC-based computers, users may need two perform a pair-wise swap of the bytes prior to using these data files. Floating-point (REAL) binary numbers are in the native Vax D-floating format. This format is no longer widely used so most of these files have also been converted to ASCII text format for convenience. 4. VOLUME CONTENTS 4.1 VOLUME NAMES The PDS originally released raw, compressed "EDR" versions of all the Voyager images on a set of CD-ROMs identified VG_0001 through VG_0038. The organization is as follows: VG_0001-0003: The complete Uranus images VG_0004-0005: Selected Saturn images VG_0006-0008: Selected Jupiter images VG_0009-0012: The complete Neptune images VG_0013-0025: The complete Jupiter images VG_0026-0038: The complete Saturn images This derived set of volumes is identified VGISS_0001 through VGISS_0038. For simplicity, we have maintained a one-to-one correspondence between the old and new volumes. This data set comprises all the Saturn images, i.e. volumes 4, 5 and 26-38. The boundaries between volumes are chronological, as defined by Voyager's Flight Data System ("FDS") clock. Within the Saturn data set, boundaries between volumes are as follows VG_0004: Selected images 33575.27 - 43901.56 VG_0005: Selected images 43901.59 - 44304.45 VG_0026: All images 32499.21 - 33562.53 VG_0027: All images 33562.55 - 34476.28 VG_0028: All images 34476.32 - 34781.49 VG_0029: All images 34781.52 - 35028.01 VG_0030: All images 35028.06 - 35363.02 VG_0031: All images 35363.06 - 35629.19 VG_0032: All images 35629.23 - 35893.16 VG_0033: All images 35893.19 - 42278.08 VG_0034: All images 42278.14 - 43290.40 VG_0035: All images 43290.46 - 43579.44 VG_0036: All images 43579.47 - 43863.41 VG_0037: All images 43863.44 - 44157.24 VG_0038: All images 44157.28 - 44304.52 As a general rule, images beginning with 3 are from Voyager 1 and those beginning with 4 are from Voyager 2. 4.2 FILE NAMING CONVENTIONS All files are named by the associated seven-digit FDS clock count (without a decimal point) at the time the image was read out of the vidicon. For example, a file named C3456712*.* is associated with the image read out at FDS time 34567.12. For most images, this corresponds to the time when an exposure ended; however, in some circumstances (modes "BOTSIM" and "BSIMAN") both the wide-angle and narrow-angle cameras were triggered simultaneously; under these circumstances, the narrow-angle camera was read out first and the wide-angle image has an FDS number a few digits higher. In the original raw, compressed volumes, files were named Cnnnnnnn.IMQ where 'nnnnnnn' is the FDS count and "IMQ" indicates that the file is a compressed image. In this data set, the associated files have the following names: Cnnnnnnn_RAW.IMG: uncompressed, raw image. Cnnnnnnn_RAW.LBL: detached PDS label for the above. Cnnnnnnn_CLEANED.IMG: cleaned version of the image, with spikes and reseau markings erased. Cnnnnnnn_CLEANED.LBL: detached PDS label for the above. Cnnnnnnn_RESLOC.DAT: binary table of reseau marking locations. Cnnnnnnn_RESLOC.TAB: ASCII table of reseau marking locations. Cnnnnnnn_RESLOC.LBL: combined-detached PDS label for both of the above. Cnnnnnnn_CALIB.IMG: calibrated image. Cnnnnnnn_CALIB.LBL: detached PDS label for the above. Included in the label is the rough conversion factor from pixel values to absolute reflectivity. Cnnnnnnn_GEOMA.DAT: binary table of tie points for modeling the geometric distortion. Cnnnnnnn_GEOMA.TAB: ASCII table containing the same information as the above. Cnnnnnnn_GEOMA.LBL: combined-detached PDS label for both of the above. Cnnnnnnn_GEOMED.IMG: geometrically corrected version of the calibrated image. Cnnnnnnn_GEOMED.LBL: detached PDS label for the above. 4.3 DARK CURRENT FILE NAMING CONVENTIONS The SUMDARKS directory on volume VGISS_0038 contains the dark current files generated for the calibration process. They are named as follows: VGa_bb_cc[dd]_Cmmmmmmm_Cnnnnnnn_ee[_ff].IMG where a = 1 for Voyager 1; 2 for Voyager 2. bb = WA for the wide-angle camera; NA for the narrow-angle camera. cc = 11 for scan rate 1:1 21 for scan rate 2:1 31 for scan rate 3:1 51 for scan rate 5:1 101 for scan rate 10:1 dd = BS for wide-angle images taken in BOTSIM or BSIMAN mode; nothing for other images. mmmmmmm = the FDS count of the first image used to generate a mean dark current. nnnnnnn = the FDS count of the last image used to generate a mean dark current. ee = the two-digit number of images combined to generate the dark current. A leading zero is used for values less than ten. ff = ED if the image has been edited, so lines are incomplete; nothing if the image is not edited. For further details about these images, see DOCUMENTS/PROCESSING.TXT. 4.4 DIRECTORY STRUCTURE The directory structure matches that of the original Voyager image volumes. FILE CONTENTS (root) Root directory for this PDS Volume. | |-AAREADME.TXT This file. | |-ERRATA.TXT A file describing any known errors or deviations from | PDS standards. | |-VOLDESC.CAT A PDS volume object, providing a high-level | description of the volume and its contents. | |-CATALOG/ A directory containing PDS catalog information, | | providing high-level descriptions of the data, | | instruments, etc. | | | |-CATINFO.TXT Description of the files in this directory. | | | |-*.CAT PDS catalog files describing this data set. | |-DOCUMENT/ A directory containing documentation. | | | |-DOCINFO.TXT Description of the files in this directory. | | | |-*.TXT Documentation. | |-INDEX/ A directory containing an index of all the data files | | on this volume. | | | |-INDXINFO.TXT Description of the files in this directory. | | | |-INDEX.TAB An index of all the data files. | |-INDEX.LBL Detached PDS label for the above. | |-MIPL A directory containing the support files obtained from | | JPL's Multi-mission Image Processing Laboratory. Found | | only on volume VGISS_0038. | | | |-DATAINFO.TXT Description of the files in this directory. | | | |-FICOR77_VGRSCF.DAT File of calibration correction factors. | |-FICOR77_VGRSCF.LBL Detached PDS label for the above. | | | |-FICOR77_VGn_camera_filter.DAT Calibration file for each Voyager | | spacecraft, camera and filter. | |-FICOR77_VGn_camera_filter.LBL Detached PDS label for the above. | | | |-RESSAR77_VGn_camera.DAT Default blemish location files for | | each Voyager spacecraft and camera. | |-RESSAR77_VGn_camera.LBL Detached PDS label for the above. | |-SUMDARKS A directory containing the dark current images used in | | the calibration process. Found only on volume | | VGISS_0038. | | | |-DATAINFO.TXT Description of the files in this directory. | | | |-*.IMG Dark current image file. | |-*.LBL Detached label for each of the above. | |-(target name) A directory containing images nominally | associated with the given target. | |-CnnnnXXX/ When the number of files is large, the target | directory is subdivided by the first four | digits of the FDS count. | |-Cnnnnnnn_*.IMG Image files named as described above. |-Cnnnnnnn_*.DAT Binary tables named as described above. |-Cnnnnnnn_*.TAB ASCII tables named as described above. |-Cnnnnnnn_*.LBL Detached or combined-detached PDS labels. Target names used as directories are as follows: CALIB Calibration (typically dark current) images (Volumes VG_0004 and VG_0005). CALIB/DARK Alternative dark current directory (Volumes VG_0026 to VG_0038). CALYPSO DIONE ENCELADU Short for Enceladus EPIMETHE Short for Epimetheus HELENE HYPERION IAPETUS MIMAS OTHER/SKY Sky images OTHER/STAR Star images PANDORA PHOEBE PROMETHE Short for Prometheus RHEA SATURN S_RINGS TETHYS TELESTO TITAN UNK_SAT For satellites that were unnamed at the time of imaging. Many of these are now identified as the smaller moons Helene, Telesto, Calypso, Prometheus and Pandora. Note that these are nominal targets; many images contain more than one target and some images missed their intended target, so the directory structure provides nothing more than general guidance about what images may be of interest. Image search tools at the PDS Rings Node, http://pds-rings.seti.org/catalog/ may provide further guidance. 5. CONTACT INFORMATION Mark Showalter SETI Institute 515 North Whisman Road Mountain View, CA 94043 650-810-0234 mshowalter@seti.org Mitch Gordon 276-523-0341 mgordon@seti.org Danny Olson 650-810-0235 dolson@seti.org http://pds-rings.seti.org/ ============================================================================== ACKNOWLEDGMENTS ============================================================================== We recognize the contribution of Brad Smith and the Voyager Imaging Team for their work in obtaining this extraordinary data set. Mark Showalter acknowledges James Pollack and Jeff Cuzzi for teaching him so many of the ins and outs of Voyager image calibration and processing. We thank JPL's Multimission Image Processing Laboratory for writing and maintaining the VICAR software. The peer review panel for this data set is TBD. ============================================================================== DISCLAIMER ============================================================================== Although considerable care has gone into making this volume, errors are both possible and likely. Users of the data are advised to exercise the same caution as they would when dealing with any other unknown data set. Reports of errors or difficulties would be appreciated. Please contact Mark Showalter or Mitch Gordon at the addresses listed above.