Visions of Saturn 2/Visions of Saturn 2.iso/readme.txt

Text File | 1994-02-07 | 10KB | 217 lines

                        VISIONS OF SATURN


Visions of Saturn, Volumes I and II offer the following selection
of NASA images:


  Images of SATURN in the Range 33575.27 - 43901.56 in GIF Format.

         Introduction

The pictures on this CD-ROM were taken by NASA'S Voyagers 1 and 2
spacecraft during their epic tours of the solar system.  NASA has
made these images available to researchers and libraries and with
this disk we make them available to the computer hobbyist.

These are full resolution (800 pixels by 800 scan lines) digital
images returned by the Voyager cameras and represent the best
nearest-encounter images for the planet and its moons.  No
additional processing has been performed to enhance the images.

The image files are contained in directories named after the
principal target of the image.  In alphabetical order, the image
directories for the Saturn volumes are:

  CALIB                 - Calibration images
  CALYPSO               - Images of satellite Calypso
  DIONE                 - Images of satellite Dione
  ENCELADU              - Images of satellite Enceladus
  EPIMETHE              - Images of satellite Epimetheus
  HELENE                - Images of satellite Helene
  HYPERION              - Images of satellite Hyperion
  IAPETUS               - Images of satellite Iapetus
  JANUS                 - Images of satellite Janus
  MIMAS                 - Images of satellite Mimas
  PANDORA               - Images of satellite Pandora
  PHOEBE                - Images of satellite Phoebe
  RHEA                  - Images of satellite Rhea
  SATURN                - Images of Saturn
  S_RINGS               - Images of the rings of Saturn
  TELESTO               - Images of satellite Telesto
  TETHYS                - Images of satellite Tethys
  TITAN                 - Images of satellite Titan
  UTIL                  - Additional viewing programs


These images have had no enhancement processing applied to them and
are "as received" from deep space.  Why not enhanced? Image
processing technology is advancing at a remarkable rate and new
techniques may not be compatible with the results of old.  So
examine these files and learn how to improve them yourself--it will
be as much fun as simply viewing them.


         File names

Each image has a unique name constructed from the clock count of
Voyager's Flight Data Sub-system (FDS).  The FDS count gives the
time at which the image was captured. The general form of a file
name is "Cxxxxxxx.yyy".  The character "C" at the beginning
designates the "xxxxxxx" as the seven digit FDS count associated
with the image.  There are two "yyy" (extensions) associated with
each image: the "GIF" extension denoting the file that contains the
actual image and the "DOC" extension denoting a file containing
technical information of interest having to do with the like named
"GIF" file.


         Image history

NASA released these images in what we'll call the "IMQ" format.
The IMQ format compressed the images using a lossless first-
difference Huffman encoding scheme.  This is a fine scheme as
far as compression efficiency is concerned; however, it has a
couple of drawbacks: the decoding is slightly more complicated than
the GIF format and the format is simply not known in the PC
community.

The "IMQ" format files were broken apart yielding the "DOC" files
on this disk and a compressed image.  The compressed image was then
expanded into its full form and re-compressed into the "GIF"
format.  This process for one CD-ROM takes days when fully
automated and running on the fastest of PCs.

The encoding of the images into the "GIF" format was completely
lossless in respect to image detail.  The "colors" that the "GIF"
files render reflect the filter used when taking the picture (noted
in the "DOC" file).  When the filter effect is not obvious a
grayscale is used.

To create a true color picture of an object it would be necessary
to take several images captured at about the same time with
different filters and combine them such that an individual pixel's
color reflected the value of the same spot through the different
filters.


         DOC files

Each of the GIF images has a separate DOC file that bears the same
filename.  These DOC files tell about the viewable image and look
something like the one below.

     /*          IMAGE DESCRIPTION
     SPACECRAFT_NAME                  = VOYAGER_1
     MISSION_PHASE_NAME               = SATURN_ENCOUNTER
     TARGET_NAME                      = TITAN
     IMAGE_ID                         = '1516S1-002'
     IMAGE_NUMBER                     = 34909.12 /*FLIGHT DATA
SUBSYSTEM (FDS)
     IMAGE_TIME                       = 1980-11-11T19:52:34Z
     EARTH_RECEIVED_TIME              = 1980-11-11T21:19:46Z
     INSTRUMENT_NAME                  = WIDE_ANGLE_CAMERA
     SCAN_MODE_ID                     = '3:1'
     SHUTTER_MODE_ID                  = BOTSIM
     GAIN_MODE_ID                     = LOW
     EDIT_MODE_ID                     = '1:1' /*FULL RESOLUTION
     FILTER_NAME                      = CH4_JS
     FILTER_NUMBER                    = 0
     EXPOSURE_DURATION                = 15.3600 <SECONDS>
     NOTE                             = "MULTISPECTRAL LONGITUDE
COVERAGE"


The individual specifications are broken out as follows:

SPACECRAFT_NAME    = Spacecraft name associated with the image.
                     Valid values are VOYAGER_1 and VOYAGER_2.

MISSION_PHASE_NAME = Name of mission phase for this image
                     (URANUS_ENCOUNTER, JUPITER_ENCOUNTER,
                     SATURN_ENCOUNTER, or NEPTUNE_ENCOUNTER).

TARGET_NAME        = Observational target of the image.

IMAGE_ID           = Image identification, which takes the form:
                     nnnnes+ddd, where 'nnnn' = picture sequence
                     number for a given day, 'e' = planet of
                     encounter (J=Jupiter, S=Saturn, U=Uranus,
                     N=Neptune), 's' = Voyager spacecraft (1 or 2),
                     - sign indicates before and a + sign indicates
                     after closest planetary approach.   'ddd' =
                     number of days from closest approach.

IMAGE_NUMBER       = The unique number which identifies this image.
                     IMAGE_NUMBER is extracted from the Flight Data
                     Subsystem (FDS) clock count at time of image
                     acquisition.  For Voyager images the number is
                     a seven-digit value, with 5 digits to the left
                     of the decimal point (the modulo 16-bit
                     (65536) count and 2 digits to the right of the
                     decimal point (the modulo 60 count).

IMAGE_TIME         = Time at which image was acquired, in the
                     format yyyy-mm-dd-hh:mm:ss.  The time system
                     is Universal Time (UTC).  'yyyy' = year, 'mm'
                     = month, 'dd' = day of month, 'hh' = hour,
                     'mm' = minute, 'ss' = second.

EARTH_RECEIVED_TIME = Time at which image data was received on
                      earth, in the format yyyy-mm-dd-hh:mm:ss.
                      The time system is Universal Time (UTC).
                      'yyyy' = year, 'mm' = month, 'dd' = day of
                      month, 'hh' = hour, 'mm' = minute, 'ss' =
                      second.

INSTRUMENT_NAME    = Camera used to acquire the image.  Values are
                     NARROW_ANGLE_CAMERA or WIDE_ANGLE_CAMERA.

SCAN_MODE_ID       = Scan rate of vidicon read out.  Values can be
                     '1:1', '2:1', '3:1', '5:1', and '10:1'. The
                     instrument scan rate affects the radiometric
                     properties of the camera because of the dark
                     current buildup on the vidicon.

SHUTTER_MODE_ID    = Instrument shutter mode. Permitted values are:

   NAONLY - narrow angle camera shuttered only;
   WAONLY - wide angle camera shuttered only;
   BOTSIM - both cameras shuttered simultaneously;
   BSIMAN - BOTSIM mode followed by NAONLY;
   BODARK - shutter remained closed for narrow and wide angle
            camera;
   NADARK - narrow angle read out without shuttering;
   WADARK - wide angle read out without shuttering.

GAIN_MODE_ID       = Gain mode (LOW or HIGH) of the camera.

EDIT_MODE_ID       = Edit mode of the camera.  Values are
                     '1:1',which indicates the full resolution of
                     the vidicon, and '3:4', '1:2', '1:3', '1:5',
                     and '1:10' for partial resolution images.
                     Indicates amount of data read from the
                     vidicon.

FILTER_NAME       = Optical filter used for the image.  Permitted
                    values are CLEAR, CH4_U, CH4_JS, UV, VIOLET,
                    BLUE, GREEN, ORANGE, and NAD.

FILTER_NUMBER     = Optical filter number, contains the unique
                    number associated with the optical filter for
                    the image.  Needed to differentiate between the
                    two CLEAR filters on the Voyager narrow angle
                    camera.

EXPOSURE_DURATION = Exposure duration for the image, in seconds.

NOTE              = Observational intent of the image.


     Final note:

We would like to thank NASA for making this project possible.

                         WeMake CDs, Inc.
                      Indianapolis, Indiana