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)