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                  PREMAGELLAN RADAR AND GRAVITY DATA

               Selected Planetary and Gravity Data Sets


    This compact read-only optical disk (CD-ROM) contains a suite of
derived radar data sets for Venus, the Moon, Mercury, Mars, and Earth,
together with gravity data derived from tracking the Pioneer-Venus
Orbiter and the Mars Viking Orbiters.  The intent is to make available
in a compact form through the Planetary Data System (PDS) a collection
of relevant radar and gravity data before Magellan begins sending back
extensive observations in the summer of 1990.  The generation of this
CD-ROM was sponsored by both the PDS and the Magellan Project.

    This AAREADME.TXT file is the first of three nondirectory files
located in the top level directory of this CD-ROM.  The file VOLDESC.SFD
contains an overview of the data sets on this CD-ROM and is written in a
format that is designed for access by computers.  The file TEMPLATES.TXT
contains the PDS central node catalog information describing the data
sets on this disk.  All other files are located in directories below the
top level directory.  The directory DOCUMENT contains a text file named
VOLINFO.TXT that describes the CD-ROM organization, the format and
content of each of the data sets, and background information and
references needed to understand the data set processing histories.  It
is recommended that you read the VOLINFO.TXT document before trying to
extract data files.  The DOCUMENT directory also contains a file called
VICAR2.TXT, which contains a description of VICAR2 labels.  The
directory INDEX contains a number of index files.  These files are
tables in text form that have descriptive information about some of the
data sets on this CD-ROM.  While indexes can be visually scanned, they
have been designed so that they can also be loaded into most database
systems for fast and efficient searching.

    Actual data set files and associated detached labels are included in
a series of directories that group relevant data together.  The detached
labels utilize the Object Description Language (ODL) developed by the
PDS.  An ODL label is readable by both humans and computers and provides
a formal description of the format and content of the file.  For the
AAREADME.TXT, VOLDESC.SFD, and VOLINFO.TXT files, the ODL label appears
at the beginning of the respective file.  All other files have detached
labels.  A pointer in the label file indicates the file that the label
describes.  External label files have a '.LBL' file extension.  For more
information about the Object Description Language, see the document file
VOLINFO.TXT.  Note that for user convenience and compatibility with
expected Magellan data products, a number of data files have embedded
VICAR2 labels in addition to the detached labels.  See the VOLINFO.TXT
and VICAR2.TXT files for details, both in directory DOCUMENT.

    This Pre-Magellan CD-ROM of selected radar and gravity data has been
produced by the NASA Planetary Data System (PDS) and the Magellan
Project.  Specifically, Edward Guinness, Susan Slavney, and Raymond
Arvidson of the Geosciences Discipline Node at Washington University,
St. Louis, Missouri, with assistance of David Acevedo, Jet Propulsion
Laboratory, gathered the data sets and documentation from relevant
members of the science community, and generated the PDS labels and
documentation.  Michael Martin and Jason Hyon of the PDS Central Node at
the Jet Propulsion Laboratory performed the premastering of the CD-ROMs.

    A list of hardware and software that may be used to read this CD-ROM
is available from the PDS Geosciences Node at Washington University.
This list is usually distributed with the CD-ROM.

    The following individuals contributed data and documentation for
this CD-ROM data set collection:

    Bruce Bills, Lunar and Planetary Institute
    Don Campbell, Cornell University
    Pamela Clark, Jet Propulsion Laboratory
    Peter Ford, Massachusetts Institute of Technology
    Raymond Jurgens, Jet Propulsion Laboratory
    Robert Mehlman, University of California - Los Angeles
    Gordon Pettengill, Massachusetts Institute of Technology
    Roger Phillips, Southern Methodist University
    Jeffrey Plaut, Washington University
    William Sjogren, Jet Propulsion Laboratory
    Thomas Thompson, Jet Propulsion Laboratory
    Stanley Zisk, University of Hawaii