Data Set Overview
  =================
    This data set contains stellar occultation data from the 1989
    occultation of 28 Sagittarii (28Sgr) by Saturn obtained by the 1.0
    meter telescope (ESO1) at the European Southern Observatory. Data
    include occultation profiles for both ingress and egress which
    each cover a radial slice from the outer edge of Saturn's
    atmosphere to beyond the orbit of the F-ring.
 
    Ring profiles are archived as resampled normal optical depth
    profiles. Geometry solutions and noise models are also provided.
 
 
  Parameters
  ==========
    The data were obtained at 3.4 microns, using InSb nitrogen-
    cooled aperture photometers in the chopping mode. The chopping
    frequency was 8 Hz with a 68-arcsec E-W throw. The effective
    focal ratio was f/35, and 5-arcsec diaphragms were used to
    minimize background noise. Data were recorded digitally at 100 Hz.
 
 
  Processing
  ==========
    No information is available concerning the preliminary reduction
    of the data.
 
    The fully processed and resampled ring profiles have been
    generated as follows:
 
      (1) Observations of the 28 Sgr occultation made from several
      observatories were combined with Voyager PPS and RSS data sets
      to determine precisely the ring radial scale and the Saturn pole
      orientation (FRENCHETAL1993, HUBBARDETAL1993,
      NICHOLSONETAL2000).
 
      (2) Using the improved ring radial scale, the time-series of raw
      samples was converted to a uniformly-spaced series of radial
      samples. The spatial sampling interval used was 10 km,
      corresponding to Nyquist-sampled data based on the apparent star
      diameter of approximately 18 km.
 
      (3) Raw data DN levels were converted to normalized flux based
      on the viewing geometry, and subsequently to normal optical
      depth.
 
 
  Data
  ====
 
    Derived profiles (DATA/ESO1M sub-directory)
    -------------------------------------------
      The resampled data are presented in seven column ASCII tables.
      The columns are (1) radius(km), (2) normalized flux, (3) sigma
      flux, (4) normal optical depth(tau), (5) tau lower, (6) tau
      upper, (7) quality flag.
 
      The quality flag has five possible values. They are: 0=ok, 1=tau
      greater then tau_max, 2=non-photometric, 3=corrupted data,
      4=missing data. For detailed discussion of the model used to
      determine noise and reasonable values for optical depth see
      MODEL.TXT in the DOCUMENTS sub-directory.
 
      In general, for corrupted or missing data, dummy values of
      9.9990 are used in columns 3-6.
 
 
  Ancillary Data
  ==============
    Browse data (BROWSE/ESO1M sub-directory)
    ----------------------------------------
      This subdirectory contains two types of plot for each
      observation run.
 
      Plots of radial profiles of stellar flux normal optical depth of
      the rings as derived from the observations of the 28 Sgr
      occultation by the rings of Saturn. Each plot is based on the
      corresponding profile data file in the corresponding
      subdirectory of the DATA directory.
 
      Plots of ancillary geometry information. Each plot is based on
      the corresponding profile data file in the corresponding
      subdirectory of the GEOMETRY directory.
 
 
    Geometry information (GEOMETRY/ESO1M sub-directory)
    -------------------------------------
      The geometry information is provided in separate files for
      ingress and egress. Data are arranged in four columns:
 
        a) Equatorial Radius (Km),
        b) Observatory received time (UTC),
        c) Ring Plane inertial longitude of the intercept point (deg),
        d) delta time (s). The latter is a correction factor used when
           determining the line-of-sight distance between the ring
           intercept point and the observer. The data are presented
           with uniformly varying radius (1000 km increments) between
           73,000 km and 142,000 km.
 
      The data are arranged in the order of increasing radius
      regardless of whether the observation is ingress or egress.
      Geometry data were obtained using a polynomial fit. The
      polynomial coefficients can be found in DOCUMENTS/POLY_CO.TXT
 
 
  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.
 
  Media/Format
  ============
    This data set is archived on compact disc (CDROM) media.
    Organization and formats are according to PDS and ISO 9660
    level 2 standards.
 
    Most binary data files are in least-significant-byte first, which
    is the native format for PCs and Digital workstations.  Users of
    Suns and other workstations may need to swap bytes in some data
    files before use. Note that the software tools provided on this
    volume swap the bytes automatically if this is necessary.

Confidence Level Overview
  =========================
    Overall the confidence level is good. Flawed data are clearly
    identified by non-zero values for the quality flag.
 
 
  Peer Review
  ===========
    Peer review of this data set was completed in February 2005. The
    peer reviewers were Shawn Brooks (JPL), Richard G. French
    (Wellesley College), Colleen A. McGhee (Wellesley College), Cathy
    Olkin (South West Research Institute), and Leslie Young (South
    West Research Institute). The data set was also reviewed at the
    PDS Engineering Node by Steven L. Adams.
 
 
  Data Coverage and Quality
  =========================
    Observing conditions were good throughout the occultation. The
    average seeing was 1.2 arcsec in the visible and 1.4 arcsec in the
    infrared. Atmospheric immersion occurred during the C Ring
    occultation, commingling ring features with the spikes in the
    atmosphere occultation light curve. Nonetheless, identifiable ring
    features could be measured throughout most of the ingress and
    egress occultations.
 
    There is some evidence of timing problems with this data set.
    These observations should be treated as providing accurate
    relative measurements of the times of ring features, but not
    accurate absolute ring event times. For a more detailed
    discussion, see FRENCHETAL1993.