Data Set Overview
    =================
      The data set contains Jovian 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 primary emphasis of this data set is on parameters derived
      from spectral measurements of Jupiter's Great Red Spot (GRS)
      and surrounding regions.  The results included in the records
      between FDSC 1636631 and 1636729 are from a sequence known as
      the 'GRS Cross' acquired from Voyager 1.  This consists of
      north-south and east-west scans through the GRS.  In most
      cases, two measurements were made at each pointing location.
      The diameter of the IRIS field of view on the planet
      corresponds to about one-fifth of the east-west dimension of
      the spot.  Data records with FDSCs between 2062839 and 2063011
      contain derived parameters for a Voyager 2 GRS mosaic at
      somewhat higher resolution.  The remaining records in the data
      set are from miscellaneous Voyager 1 observational sequences.
 
      The derived atmospheric parameters include retrieved
      atmospheric temperatures at the 143 mbar and 267 mbar levels,
      the fraction of the molecular hydrogen in the para state in a
      layer nominally centered near 300 mbar, cloud optical depths at
      226 cm**-1 and 2050 cm**-1, and the ammonia mole fraction at
      600 mbar relative to the equivalent solar value (0.000178).
      The methods used for retrieving the para hydrogen fraction and
      atmospheric temperatures are discussed in
      [CONRATH&GIERASCH1984], while the retrieval algorithms used to
      obtain the cloud optical depths and the ammonia abundance are
      described in [CONRATH&GIERASCH1986].
 
      To obtain the para hydrogen fraction and the atmospheric
      temperature in the upper troposphere, measurements were used in
      the S(0) and S(1) collision-induced spectral lines of molecular
      hydrogen, which result from transitions between para and ortho
      states, respectively.  If a measurement in the S(1) line is
      combined with a measurement in the S(0) line 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.  This principle forms the basis of the algorithm used
      for the rapid estimation of para hydrogen and temperature from
      the measured spectra.  Measurements near 520 and 600 cm**-1 in
      the S(1) 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 330 cm**-1 in the S(0) line 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.
 
 
    Processing
    ==========
      The algorithms used for the retrieval of the cloud optical
      depths and the ammonia abundance are discussed in
      [CONRATH&GIERASCH1986].  The cloud optical depth near 5
      micrometers is based on brightness temperature measurements in
      a spectral band 100 cm**-1 wide centered at 2050 cm**-1.  In
      this spectral region it was found that scattering must be taken
      into account in the analysis.  This was accomplished using a
      2-stream radiative transfer approximation.  The required value
      of the single scattering albedo was inferred to be
      approximately 0.75, based on IRIS measurements of spectral
      radiance as a function of emission angle.  Next, the ammonia
      abundance was inferred from a measurement in an ammonia
      absorption line at 216 cm**-1.  Finally, the cloud optical
      depth near 50 micrometers was inferred from a measurement at
      225 cm**-1 in the continuum between ammonia lines.  The
      residual ammonia gas absorption was taken into account, using
      the previously inferred ammonia abundance.
 
      In these retrievals, a single cloud layer was invoked with a
      base pressure of 680 mbar and a scale height equal to 0.14
      times the gas scale height.  The ammonia vertical distribution
      was modeled with a scale height equal to that of the cloud
      above 680 mbar and with a mole fraction independent of height
      at deeper levels.  Results from these retrievals have been
      presented in [SADAETAL1996].
 
 
    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 - 0.005 at low latitudes, increasing to + or - 0.010 at
      high latitudes.  The formal error in the retrieved temperatures
      due to noise propagation is approximately + or - 0.5 kelvin,
      while the fractional error in the optical depths and the
      ammonia abundance is estimated at + or - 10%.  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] and
      [CONRATH&GIERASCH1986].
 
      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 records included here
      is reasonably accurate.  The SEDRs used in the construction of
      this data set were generated in 1991, and C-smithing 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)