CCSD3ZF0000100000001NJPL3IF0PDS200000001 = SFDU_LABEL RECORD_TYPE = STREAM OBJECT = TEXT NOTE = "Introduction to this CD-ROM volume." PRODUCT_CREATION_TIME = 1991-03-12 END_OBJECT END Mission to Mars Selected Viking Orbiter Images in Compressed Format This compact read-only optical disk (CD-ROM) is one of a series of CD-ROM volumes containing images taken by the Visual Imaging Subsystems (VIS) on NASA's twin Viking Orbiter spacecraft. These images are copies of the Experiment Data Record (EDR) images. EDR images contain 8-bit digital numbers that are proportional to the original VIS instrument data. To produce the EDRs the original 7-bit instrument data were multiplied by 2 to convert the data to 8 bits. No other processing has been performed on the EDR image data. Thus, processing to perform radiometric and geometric calibration, removal of noise, and interpolation of missing data may be required to interpret the images. EDR images on this CD-ROM have been compressed so that more data can be fit onto each CD-ROM volume. The image data can be restored to their uncompressed format using algorithms described in documentation on this disk. Image decompression software in several programming languages is also included on the disk. This file is one of only a few files located in the main directory. Another file, VOLDESC.SFD, contains a description of the contents of this CD-ROM volume in a format that is designed for access by computers. All other files are located in directories below the main directory. The directory named DOCUMENT contains a text file named VOLINFO.TXT that describes in detail the organization of this disk and the format and content of the Viking Orbiter images. It is recommended that you read the VOLINFO.TXT document before trying to process image files. The DOCUMENT directory also contains a text file named ERRATA.TXT, which is a cumulative summary of comments and errors concerning the Viking Orbiter images published so far on CD-ROM. The directory named INDEX contains the files IMGINDEX.TAB and CUMINDEX.TAB. These tables have descriptive information about the images on this volume (in IMGINDEX.TAB) and about the images on all the volumes in this series (in CUMINDEX.TAB). The index tables are text files in a format that can be read by people and computers. The tables have been designed so that they can be loaded into most database systems for fast and efficient searching. The file named INDXINFO.TXT in the INDEX directory describes how to use the index tables. The files IMGINDEX.LBL and CUMINDEX.LBL describe the format of each field in the tables. The directory named SOFTWARE contains source code and executable versions of image decompression software written in FORTRAN, C, and VAX Macro assembly language. There is one executable decompression program for IBM PCs and another for VAX VMS systems. The file named SOFTINFO.TXT in the SOFTWARE directory describes the software in detail. The compressed image files are contained in directories named after the spacecraft orbit in which the images were acquired. If there were no images acquired during an orbit, the directory for that orbit is omitted. Some Viking Orbiter images either were not available on the magnetic tapes used to generate the CD-ROM or the magnetic tape data were corrupted. We are attempting to recover such images from the Master Data Record (MDR) tapes for the Viking Mission. Because of the additional processing required to recover these images, some of them may not be ready in time to be included on this CD-ROM. These images will be included on a later CD-ROM within this series. There is also a subsampled version of each compressed EDR image on this CD-ROM. The subsampled images, which are referred to as browse images, consist of every fourth sample of every fourth scan line. This produces an image of 300 samples and 264 scan lines. Browse images have also been processed to remove noise and interpolate missing data that often occurs in Viking Orbiter images. Browse images can be used to quickly locate an image of interest. All of the browse images are located in subdirectories under the BROWSE directory. The subdirectories of the BROWSE directory are organized by orbit number in the same manner as the compressed image files. Most files on this disk have a label encoded in the Object Description Language (ODL) developed by the Planetary Data System (PDS). An ODL label is readable by both humans and computers. It provides a formal description of the format and content of a file. For most files the ODL label appears at the beginning of the file (as is the case for this file). All image files have an embedded ODL label preceding the data in the file. For files where labels cannot be easily included, a separate file is provided that contains the ODL label. A pointer in the label file indicates which file the label describes. External label files have a '.LBL' extension. For a description of the Object Description Language, see the document file VOLINFO.TXT in the DOCUMENT directory. The LABEL directory contains two files in ODL format that describe the structure of the engineering information contained within each image file. The LABEL directory also has a text file named CATALOG.LBL that contains the PDS catalog information about the Viking Orbiter mission and the VIS instruments. The set of Viking Orbiter image CD-ROMs has been produced by the NASA Planetary Data System (PDS) with involvement of the Discipline Nodes. Specifically, Edward Guinness and Susan Slavney, Geosciences Discipline Node at Washington University, St. Louis, Missouri, performed the data compression and label checking; Eric Eliason, Image Node at the U.S. Geological Survey, Flagstaff, Arizona, led the software development and recovery of images from the MDR tapes; and Jason Hyon and Michael Martin, PDS Central Node at the Jet Propulsion Laboratory, Pasadena, California, performed the premastering of the CD-ROMs.