Data Set Overview
    =================
      The data set contains Saturn atmospheric parameters derived
      from spectra obtained with the Voyager infrared interferometer
      spectrometer (IRIS).  The data set is ordered by time as
      measured by the Flight Data System Count (FDSC).  This
      represents the data frame number; the last two digits are
      modulo 60.  Also included in the data set are information on
      pointing and associated geometry of the measurements and
      brightness temperatures obtained from measured radiances at
      selected wavenumbers.
 
 
    Parameters
    ==========
      The measurements were obtained during a north/south mapping
      sequence in which the planet was mapped in the latitude range
      between approximately 60 S and 60 N.  The instrument was
      repeatedly scanned from north to south as Jupiter rotated under
      the spacecraft through approximately 360 degrees of longitude.
      The map was taken as the spacecraft approached Saturn on the
      day side of the planet.
 
      The derived atmospheric parameters include retrieved
      atmospheric temperatures at the 152 mbar and 286 mbar levels,
      and the fraction of the molecular hydrogen in the para state in
      a layer nominally centered near 300 mbar.  The methods used for
      retrieving the para hydrogen fraction and atmospheric
      temperatures are discussed in [CONRATH&GIERASCH1984].
 
      To obtain the para hydrogen fraction and the atmospheric
      temperature in the upper troposphere, measurements were used in
      the S(0) collision-induced spectral line of molecular hydrogen
      and its low wave number wing.  If a measurement in the S(0)
      line is combined with a measurement in the line wing at a
      similar nominal optical depth, then because of the differing
      sensitivity to the ortho-para hydrogen ratio, it is possible to
      estimate both an atmospheric temperature and a para hydrogen
      fraction.
 
 
    Processing
    ==========
      This principle forms the basis of the algorithm used for the
      rapid estimation of para hydrogen and temperature from the
      measured spectra.  Measurements near 300 and 350 cm**-1 in the
      S(0) line were first used to retrieve temperature in the upper
      troposphere, taking into account the emission angle appropriate
      to the measurements.  The resulting atmospheric temperatures
      were then used to calculate theoretical brightness temperatures
      at 250 cm**-1 for comparison with measured values to determine
      the para hydrogen fraction.  In the interest of computational
      speed, the synthetic brightness temperatures were calculated
      for only two values of the para hydrogen fraction, and the
      final para hydrogen fraction estimate is obtained from the
      measured brightness temperature by linear interpolation.  This
      retrieval pertains to an atmospheric layer that is nominally
      centered near 300 mbar and moves upward with increasing
      emission angle.
 
 
    Ancillary Data
    ==============
      In addition to the retrieved atmospheric parameters, integrated
      measurements from the broad band visible radiometer are
      included, along with brightness temperatures associated with
      the radiances used in the retrievals.  The emission angle and
      the solar zenith angle for the central point of the field of
      view projected onto the planet are provided along with the
      slant distance (in km) from the spacecraft to the central
      point.  The latitude and longitude of the central point are
      given as are the coordinates of eight additional points equally
      spaced around the periphery of the field of view.

Confidence Level Overview
    =========================
      In evaluating the confidence level of a given data record,
      several factors should be taken into account.  These include
      the propagation of measurement noise, the uncertainties
      introduced by modeling assumptions that are incorporated in the
      algorithms, and pointing uncertainties.
 
      An estimate of the error in the para hydrogen fraction from an
      individual measurement due to instrument noise propagation only
      is + or - 0.01 at low latitudes, increasing to + or - 0.02 at
      high latitudes.  The formal error in the retrieved temperatures
      due to noise propagation is approximately + or - 1 kelvin.  The
      systematic errors due to modeling assumptions cannot be easily
      estimated.  The user should become thoroughly familiar with
      these assumptions, as they may pertain to his or her particular
      application, by referring to [CONRATH&GIERASCH1984].  Note the
      data records include fields for two cloud optical depths and an
      ammonia abundance; however, these fields do not contain
      physically meaningful values for Saturn, but have been retained
      to permit use of the same format for both Jupiter and Saturn
      data sets.
 
      The pointing information for each record is used both to locate
      the data on the planet and to calculate the emission angle
      required in the retrievals.  The quoted 3-sigma uncertainty in
      the pointing data taken from the Supplementary Experimenter
      Data Records (SEDR) is 0.15 degrees (compared with the 0.25
      degree diameter IRIS field of view).  (A SEDR consists of a
      tape of spacecraft and instrument-specific geometric
      information supplied by the Voyager project.) In addition,
      there are sometimes systematic errors in the SEDR pointing
      values for entire data sequences or links that take the form of
      approximately constant offsets in the given field of view
      locations on the planet.
 
 
    Data Coverage and Quality
    =========================
      It is believed that the pointing for the Saturn incoming
      north/south map sequence is reasonably accurate.  The SEDRs
      used in the construction of this data set were generated in
      1991, and C-smithing, which makes use of imaging to introduce
      corrections, was employed.  It should be noted that earlier
      versions of SEDRs were used for obtaining the pointing
      information that is included with the IRIS spectral data sets.
      As a consequence, the pointing given in the present data set
      may not be in exact agreement with that included with the
      spectral data sets.
 
      When attempting to correlate IRIS data with those from other
      Voyager instruments, it may be necessary to take into account
      the relative offsets of the centers of the fields of view of
      the various instruments.  Offsets relative to the center of the
      ISS Narrow Angle camera field of view are given in the tables
      below.  Elevation is positive to the right within the imaging
      field of view and cross elevation is positive downward.  The
      offsets are expressed both in degrees and in Narrow Angle
      pixels.
 
        Voyager 1:
 
          Instrument   Elevation    Cross-Elevation
 
          IRIS         +0.020 deg     +0.024 deg
                     (+37.7 pixels) (+45.3 pixels)
 
          ISS(WA)      +0.0315 deg    +0.0247 deg
                     (+59.4 pixels) (+46.6 pixels)
 
          UVS          +0.010 deg     -0.030 deg
                     (+18.9 pixels) (-56.6 pixels)
 
 
        Voyager 2:
 
          Instrument   Elevation    Cross-Elevation
 
          IRIS         +0.016 deg     -0.009 deg
                     (+30.2 pixels) (-17.0 pixels)
 
          ISS(WA)      -0.0308 deg    -0.0068 deg
                     (-58.1 pixels) (-12.8 pixels)
 
          UVS           0.0 deg       +0.08 deg
                       (0.0 pixels)(+150.9 pixels)
 
          PPS          -0.06 deg      +0.003 deg
                    (-113.2 pixels)  (+5.7 pixels)