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PDS_VERSION_ID                   = PDS3
LABEL_REVISION_NOTE              = "M.R. SHOWALTER, 2003-12-05"
RECORD_TYPE                      = STREAM

OBJECT                           = DATA_SET
  DATA_SET_ID                    = "VG1/VG2-SR/UR/NR-UVS-2/4-OCC-V1.0"
  OBJECT                         = DATA_SET_INFORMATION
  DATA_SET_NAME                  =

  CITATION_DESC                  = "Showalter, M.R., P.D. Nicholson,
A.L. Broadfoot, W.T. Forrester, and J.B. Holberg, VG1/VG2 SR/UR/NR
Data System, 2004."

  DATA_OBJECT_TYPE               = SERIES
  START_TIME                     = 1980-08-23T00:00:00
  STOP_TIME                      = 1989-10-03T00:00:00
  DATA_SET_RELEASE_DATE          = 2003-12-31

  DATA_SET_TERSE_DESC            = "
This data set contains stellar occultation data from the Voyager
Ultraviolet Spectrometer. It includes ring profiles from Saturn,
Uranus and Neptune at several levels of processing, plus geometry and
calibration files, software and documentation."

  DATA_SET_DESC                  = "

  Data Set Overview
    This data set contains stellar occultation data obtained by the
    Voyager Ultraviolet Spectrometer (UVS). It includes ring
    occultation profiles from Saturn, Uranus and Neptune. It does not
    include other types of data obtained by the Voyager UVS.

    The specific ring occultation experiments carried out by UVS

    Planet   Star       Direction  Vgr Comments
    Saturn   iota Her   egress      1  Inner C Ring only
    Saturn   delta Sco  ingress     2  Inner C Ring only
    Saturn   delta Sco  egress      2  Entire ring system
    Uranus   sigma Sgr  both        2  Delta, Lambda and
                                       Epsilon rings only
    Uranus   beta Per   both        2  All rings
    Neptune  sigma Sgr  ingress     2  All rings

    Ring profiles are archived in a variety of formats, from raw data
    to calibrated and resampled optical depth profiles. Processing
    software, geometry solutions and calibration models are also

    Raw data files contain a time series of spectra, where each
    spectrum consists of 126 wavelength samples. UVS counts are
    proportional to the number of photons received, with roughly 2.5
    UVS counts per photon. Samples are time-tagged by Voyager's
    internal clock, the Flight Data System (FDS) count. Sampling
    intervals are 0.32 sec in occultation mode.

    Data are archived at a variety of levels of processing. The fully
    processed, resampled and calibrated ring profiles have been
    generated as follows:

    (1) Raw data files are edited to flag missing and invalid data and
    are padded as necessary to yield a continues, uniformly-spaced
    time series of data.

    (2) To improve signal-to-noise ratio, a selected range of
    wavelengths is summed to yield a single value.

    (3) A geometry model is used to match up each raw sample in the
    edited data file with the corresponding intercept point in the
    ring plane. The GEOMETRY directory contains these files; in some
    cases a geometry file comes in several versions to record the
    differing geometry solutions that various investigators have

    (4) A calibration model is used to determine the number of
    background photons and the number of stellar photons corresponding
    to a given sample. The CALIB directory contains these files. As
    with geometry, multiple calibration models are provided for many

    (5) Using the geometry model, the time-series of raw samples is
    converted to a uniformly-spaced series of radial samples, in which
    each new radial sample is calculated via a weighted average of the
    relevant raw samples. Invalid and missing samples are
    zero-weighted at this step.

    (6) Using the weighting function described above and the known
    noise properties of the raw data, the uncertainty in each
    resampled value is calculated.

    (7) Resampled photon count values are converted to ring opacity
    tau using the calibration model, via the following formula:

    measured_counts = background_counts + stellar_counts*exp(-tau/mu)

    where mu is the cosine of the emission angle (listed in the labels
    of the geometry files).

    (8) By adding or subtracting the derived uncertainty from the
    measured count value and then solving the formula above for tau,
    the confidence interval on the ring opacity is derived.

    A variety of data files are included on this volume.

    Source data (SORCDATA directory)
      The (typically) binary data files as contributed to the Rings
      Node by several investigators. These files are provided for
      documentation purposes and are not otherwise supported.

    Raw data (RAWDATA directory)
      These files contain essentially the same data as are found in
      the SORCDATA directory, but with time tags corrected.

    Edited data (EDITDATA directory)
      Edited versions of the raw data, padded with empty records to
      represent continuous, uniformly-spaced time-series of UVS
      spectra and spectral sums. Invalid and missing data samples are
      flagged. These are the easiest binary files to use and are
      recommended for most purposes.

    Derived profiles (EASYDATA directory)
      Easy-to-use ASCII data files containing ring opacity and its
      uncertainty vs. radial location in a ring system. Files are
      included at a variety of radial resolutions: 0.2, 0.5, 1, 2, 5,
      10, 20 and 50 km per sample. Because the rings of Uranus are
      narrow and inclined, there are separate profiles for each
      Uranian ring.

      Also provided are calibrated ring profiles that have not been
      radially resampled. Instead, they are subsampled at integer
      multiples of the original spacing.

  Ancillary Data
    Many different types of ancillary data files are provided to
    document the PPS experiments and to describe the geometry and
    calibration during each occultation.

    Geometry models (GEOMETRY directory)
      ASCII data files, containing a description of the ring intercept
      geometry at times matching the data records in each
      corresponding edited data file. Because the rings of Uranus and
      Neptune are inclined, there are separate geometry files for each
      ring of these planets.

    Trajectory models (TRAJECT directory)
      ASCII data files, containing a position and velocity of Voyager
      relative to the center of the planet at times matching the data
      records in each corresponding edited data file.

    Calibration models (CALIB directory)
      ASCII data files, containing the modeled stellar and background
      photon count rates at times matching the data records in each
      corresponding edited data file.

    Noise models (NOISDATA directory)
      Edited, binary data files in which the known rings of Uranus and
      Neptune have been removed. These are used for fitting some
      calibration models. Their formats are identical to the
      corresponding edited data files.

    Support images (IMAGES directory)
      Voyager support images obtained before, during and after the
      ring occultations.

    Ephemeris files (SPICE directory)
      Voyager ephemeris files for each of the planetary encounters, in
      SPICE format. For more information about SPICE data and
      toolkits, consult the PDS Navigation and Ancillary Information
      (NAIF) Node at:

  Coordinate System
    All geometric quantities appearing in the labels are in J2000
    coordinates. In this coordinate frame, the z-axis points
    northward along the Earth's J2000 rotation axis and the x-axis
    points toward the First Point of Aries. In some cases, B1950
    coordinate values are also included.

    Included on this disk is the source code for several libraries
    of software tools designed to be used with this and other ring
    occultation data sets.

    Light Label Library (SOFTWARE/OAL directory)
      A toolkit supported by the PDS Central Node for reading and
      writing PDS labels.

    Object Access Library (SOFTWARE/OAL directory)
      A toolkit supported by the PDS Central Node for reading and
      writing data objects described by PDS labels. Built atop the
      Light Label Library.

    Profile Library (SOFTWARE/PROFILE directory)
      A toolkit supported by the PDS Ring-Moon Systems Node for manipulating
      one-dimensional profiles of planetary rings. Built atop the
      Light Label Library and the Object Access Library.

    Also included are the software tools to generate calibrated ring
    profiles at arbitrary resolution. These are the tools used to
    populate the EASYDATA subdirectories. These tools make full use of
    the above libraries.

    This data set is archived on compact disc (CDROM) media.
    Organization and formats are according to PDS and ISO 9660
    level 1 standards.

    Binary data files are provided in native formats for most
    platforms. Also, note that the software tools provided on this
    volume handle binary conversions on the fly if this is necessary."


  Confidence Level Overview

    Strong variations in overall photon count are correlated with
    instrument pointing changes, because the UVS field of view is
    narrow relative to Voyager's 'limit cycle' motion. As a result,
    sensitivity varies substantially within each single data set. The
    calibration models show these variation. Nevertheless, subtle
    features in the data that correlate with these sensitivity
    variations should be regarded with some skepticism.

    The data from the Uranus beta Per occultation were dominated by
    the charged particle background at Uranus. As a result, the rings
    are not detectable.

  Peer Review
    Peer review of this data set is in progress.

  Data Coverage and Quality

    The UVS experiments provided complete coverage of the ring systems
    of Saturn and Neptune. Only the outer part of the Uranian ring
    system is covered at reasonable sensitivity, including the Delta
    and Epsilon Rings.

    A few small, isolated gaps are present. In the edited data files,
    missing data samples have been indicated via a MISSING_CONSTANT
    flag. Unreliable samples have been replaced by an
    INVALID_CONSTANT flag. Unedited versions of the same data are
    also provided."

  END_OBJECT                     = DATA_SET_INFORMATION

  OBJECT                         = DATA_SET_TARGET
    TARGET_NAME                  = "S RINGS"
  END_OBJECT                     = DATA_SET_TARGET

  OBJECT                         = DATA_SET_TARGET
    TARGET_NAME                  = "U RINGS"
  END_OBJECT                     = DATA_SET_TARGET

  OBJECT                         = DATA_SET_TARGET
    TARGET_NAME                  = "N RINGS"
  END_OBJECT                     = DATA_SET_TARGET

  OBJECT                         = DATA_SET_HOST
    INSTRUMENT_HOST_ID           = VG2
    INSTRUMENT_ID                = UVS
  END_OBJECT                     = DATA_SET_HOST

    REFERENCE_KEY_ID             = "N/A"

END_OBJECT                       = DATA_SET

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