Data Set Overview
    =================
      This data set contains binned and splined data obtained from
      the Viking Meteorology Instrument System (VMIS) through
      portions of the Viking Lander 1 mission.  The data set consists
      of mean values of pressure, temperature, and wind speed (zonal
      and meridional) calculated for 25 bins of equal duration per
      day.  The data are presented on a bin by bin basis for Lander 1
      sol (Mars solar day after landing) 1-350, with no data existing
      between sols 117 and 133.  Failure of the wind direction
      quadrant sensor on Lander 1 sol 45 required development of data
      recovery techniques to produce wind direction information for
      periods after the failure.  For details on the data recovery
      techniques used to produce this data set, see MURPHY_1986.
      Another data set is available for an extensive period of Lander
      2 observations and the Lander 1 observations made prior to the
      sol 45 failure; refer to PDS data set id
      VL1/VL2-M-MET-4-BINNED-P-T-V-V1.0.
 
      The 1/25 of a day temporal resolution of this data set make it
      useful for the study of atmospheric motions in the martian
      subtropics and diurnal variations in atmospheric properties.
      For further background information on the VMIS and results from
      this experiment, see CHAMBERLAIN_ETAL1976, HESS_ETAL_1977,
      TILLMAN_ETAL_1979, BARNES_1980, HESS_ETAL_1980, LEOVY_1981,
      SHARMAN_RYAN_1981, MURPHY_1986, and TILLMAN_1988.
 
      This data set is composed of the following fields (listed as
      the field name followed by a description):
 
      SC_ID
       Spacecraft id
 
      SOL_LON
       Areocentric longitude of the Sun (Ls), derived for the
       local time corresponding to the beginning of each bin
 
      VIKING_YEAR
       Viking mission year, starting at 1 when the Viking
       spacecraft reached Mars, and incremented at Ls = 0
       every martian year
 
      MARTIAN_DAY
       The martian solar day (sol), starting at day 0 when
       each Lander touched down
 
      LOCAL HR_BIN
       The hour bin number, starting with 0 at local midnight
       and incremented by 1 every 1/25 of a martian day
 
      PRESS_MEAN
       The mean atmospheric pressure in each bin
 
      ZON_WND_MEAN
       The mean zonal wind speed in each bin
 
      MER_WND_MEAN
       The mean meridional wind speed in each bin
 
      TEMP_MEAN
       The mean ambient temperature in each bin
 
 
      Processing Level Id            : 4
      Software Flag                  : Y
      Processing Start Time          : 1984-09
      Processing Stop Time           : 1986-12
      Native Start Time              : 97.2 AREOCENTRIC SOL LON,
                                       EARTH YR 1976
      Native Start Time              : 298.2 AREOCENTRIC SOL LON,
                                       EARTH YR 1977
 
 
    Parameters
    ==========
 
      Data Set Parameter 'ATMOSPHERIC PRESSURE'
      -----------------------------------------
        The force per unit area exerted by an atmosphere, measured in
        millibars (10**3 dyne cm**-2).
 
        Data Set Parameter Name        : ATMOSPHERIC PRESSURE
        Data Set Parameter Unit        : MILLIBAR
        Sampling Parameter Name        : TIME
        Sampling Parameter Unit        : MARS SOLAR DAY / 25
        Minimum Sampling Parameter     : N/A
        Maximum Sampling Parameter     : N/A
        Sampling Parameter Resolution  : 1
        Sampling Parameter Interval    : 1
        Minimum Available Sampling Int : 1
        Noise Level                    : N/A
 
 
      Data Set Parameter 'TEMPERATURE'
      --------------------------------
        The temperature of a system is a measure of the heat content
        of the system, and determines if a system is in thermal
        equilibrium with other systems.
 
        Data Set Parameter Name        : TEMPERATURE
        Data Set Parameter Unit        : DEGREES CELSIUS
        Sampling Parameter Name        : TIME
        Sampling Parameter Unit        : MARS SOLAR DAY / 25
        Minimum Sampling Parameter     : N/A
        Maximum Sampling Parameter     : N/A
        Sampling Parameter Resolution  : 1
        Sampling Parameter Interval    : 1
        Minimum Available Sampling Int : 1
        Noise Level                    : N/A
 
 
      Data Set Parameter 'WIND VELOCITY'
      ----------------------------------
        The velocity of a parcel of atmosphere in motion relative to
        a reference location.
 
        Data Set Parameter Name        : WIND VELOCITY
        Data Set Parameter Unit        : METERS/SECOND
        Sampling Parameter Name        : TIME
        Sampling Parameter Unit        : MARS SOLAR DAY / 25
        Minimum Sampling Parameter     : N/A
        Maximum Sampling Parameter     : N/A
        Sampling Parameter Resolution  : 1
        Sampling Parameter Interval    : 1
        Minimum Available Sampling Int : 1
        Noise Level                    : N/A
 
 
    Source Instrument Parameters
    ============================
      Instrument Host ID              : VL1
      Data Set Parameter Name         : TEMPERATURE
      Instrument Parameter Name       : TEMPERATURE
      Important Instrument Parameters : 1
 
      Instrument Host ID              : VL1
      Data Set Parameter Name         : WIND VELOCITY
      Instrument Parameter Name       : TEMPERATURE
      Important Instrument Parameters : 1
 
      Instrument Host ID              : VL1
      Data Set Parameter Name         : ATMOSPHERIC PRESSURE
      Instrument Parameter Name       : PRESSURE
      Important Instrument Parameters : 1
 
 
    Processing
    ==========
 
      Processing History
      ------------------
        Source Data Set ID       : N/A
        Software                 : UNK
        Product Data Set ID      : VL1-M-MET-4-BINNED-P-T-V-CORR-V1.0

Overview
    ========
      The pressure transducers were calibrated to approximately 0.01
      to 0.02 millibars accuracy over the ranges expected for martian
      atmospheric pressure variation.  Calibrations to accuracies
      greater than allowed by the digitizing system were accomplished
      by test support instrumentation.  Repeatability from year to
      year of the daily average pressures indicates that the
      transducers have remained stable to significantly better than
      0.04 millibars throughout the mission, possibly maintaining
      stabilities on the order of 0.01 millibars.  Due to the binned
      nature of this data set, accuracy is not limited by the
      pressure digitization.
 
      The ambient temperature sensor consists of three thermocouples
      wired in parallel.  It is capable of measuring over the entire
      range of expected martian temperatures with an accuracy of
      about 1.5 degrees Celsius.  Problems with this sensor on Lander
      2 limit its accuracy to about 3 degrees Celsius (see
      HESS_ETAL_1977).  Note that the effects of Lander interference
      (ie, wind flowing over the lander) are not included in this
      data set.
 
      Wind speed is measured by means of two hot film anemometers
      oriented orthogonal to each other and lying in the horizontal
      plane.  These hot film elements were maintained at a nominal
      overheat temperature of 100 degrees Celsius above the air
      temperature measured by a reference temperature sensor.  The
      power required to maintain each anemometer at the specified
      temperature was a function of the component of the wind speed
      orthogonal to the element.  Wind speed accuracy is about 10%
      over most of the range (about 2-150 meters per second) but
      degrades somewhat for very light winds.  Lander interference,
      ie, wind flowing over the lander, also degrades accuracy;
      ground testing indicates that the degradation should not be
      much in excess of 10% for the system as a whole.
 
      The wind speed sensors also measure wind direction, but with a
      fourfold ambiguity.  Selection of the proper quadrant is
      accomplished by a quadrant sensor, consisting of a heated
      cylindrical platinum core (maintained at a 100 degrees Celsius
      overheat) surrounded by four thermocouple junctions at equal
      angles and distance from the core.  Thermocouples on opposite
      sides of the post comprised a thermocouple pair which was
      connected in series, allowing for measurement of the
      temperature differences across each pair.  These differences
      resulted from the thermal wake in the lee of the heated center
      core.  The quadrant sensor values were functions, though not
      single-valued, of wind speed.  The redundant wind speed and
      directional information provided by both the wind speed and
      quadrant sensors was combined using a least squares technique
      to give the best estimates of wind speed and direction.
      Overall accuracy in wind direction measurement is about 10%.
 
      Failure of the quadrant sensor on Lander 1 sol 45 (see
      HESS_ETAL_1977) required development of special data recovery
      techniques to produce wind direction information for periods
      after the failure.  For details on the data recovery techniques
      used to produce this data set, see MURPHY_1986.  Another data
      set is available for an extensive period of Lander 2
      observations and the Lander 1 observations made prior to the
      sol 45 failure; refer to PDS data set id
      VL1/VL2-M-MET-4-BINNED-P-T-V-V1.0