Data Set Overview
    =================
      This data set contains binned and splined data obtained from
      the Viking Meteorology Instrument System (VMIS) through most of
      the Viking Lander 2 mission and the early days of the Lander 1
      mission.  The data set consists of mean values of pressure,
      temperature, and wind speed (zonal, meridional, and combined)
      and relevant statistics and warning flags calculated for 25
      bins of equal duration per day.  The effect of Lander
      interference on the temperature measurements is also estimated.
      The data are presented on a bin by bin basis for Lander 1 sol
      (Mars solar day after landing) 1-45 and for Lander 2 sol 1-1050
      (with the only major gap occurring between sol 561 and 625).
      Failure of the quadrant sensor on Lander 1 sol 45 (see
      HESS_ETAL_1977) precludes unambiguous determination of wind
      direction without modification to the analysis techniques and
      software used to generate this data set (see HESS_ETAL_1977);
      therefore, this data set does not include Lander 1 measurements
      made after sol 45.  A data set which has recovered a period of
      measurements made between Lander 1 sol 1 and 350 is available;
      refer to PDS data set id VL1-M-MET-4-BINNED-P-T-V-CORR-V1.0.
 
      The 1/25 of a day temporal resolution of this data set make it
      useful for studies of atmospheric motions, periodicities of
      oscillations, and diurnal variations in atmospheric properties,
      among others..  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, and TILLMAN_1988.
 
      To assist in the utilization of these data, research users are
      requested to notify James E.  Tillman (the data set producer)
      of their use and applications for these data.  Resources
      permitting, he will communicate any warnings which may be
      applications dependent, and provide any necessary related
      documentation.  Please address inquiries to:
 
          James E. Tillman
          Department of Atmospheric Sciences, AK-40
          University of Washington
          Seattle, WA  98195
          Telephone: 206-543-4586
          NASAMAIL: JTILLMAN
 
      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 recalibrated atmospheric pressure in each bin
 
      PRESS_TOT
       The number of recalibrated pressure measurements in
       each bin
 
      PRESS_FLAG
       Warning flags concerning binned pressure values with
       missing data, no data, lander interference, and
       splined values
 
      ZON_WND_MEAN
       The mean zonal component of wind speed in each bin
 
      ZON_WND_DEV
       The standard deviation of the zonal component of wind
       speed in each bin
 
      MER_WND_MEAN
       The mean meridional component of wind speed in each bin
 
      MER_WND_DEV
       The standard deviation of the meridional component of
       wind speed in each bin
 
      WND_SPD_MEAN
       The mean combined wind speed in each bin
 
      WND_SPD_DEV
       The standard deviation of the combined wind speed in
       each bin
 
      WND_TEM_TOT
       The number of wind measurements in each bin
 
      WND_TMP_NLI
       The number of wind measurements in each bin not
       suffering from Lander interference
 
      WIND_FLG
       Warning flags concerning binned wind values with missing
       data, no data, lander interference, and splined values
 
      TAMB_NLI_MN
       The mean ambient temperature in each bin
       (No Lander interference experienced)
 
      TAMB_NLI_DEV
       The standard deviation of the ambient temperature in
       each bin (no Lander interference experienced)
 
      TREF_NLI_MN
       The mean reference temperature in each bin
       (No Lander interference experienced)
 
      TREF_NLI_DEV
       The standard deviation of the reference temperature in
       each bin (no Lander interference experienced)
 
      T_NLI_FLAG
       Warning flags concerning binned temperature values
       (no Lander interference) with missing data, no data,
       and splined values
 
      TAMB_INT_MN
       The mean Lander interference effect on the ambient
       temperature in each bin
 
      TAMB_INT_DEV
       The standard deviation of Lander interference effect
       on the ambient temperature in each bin
 
      TREF_INT_MN
       The mean Lander interference effect on the reference
       temperature in each bin
 
      TREF_INT_DEV
       The standard deviation of Lander interference effect
       on the reference temperature in each bin
 
      T_INT_FLAG
       Warning flags concerning Lander interference effects
       on temperature values with missing data, no data,
       and splined values
 
 
      Processing Level Id            : 4
      Software Flag                  : Y
      Processing Start Time          : UNK
      Processing Stop Time           : UNK
      Native Start Time              : 97.2 AREOCENTRIC SOL LON,
                                       EARTH YR 1976
      Native Start Time              : 342.0 AREOCENTRIC SOL LON,
                                       EARTH YR 1979
 
 
    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              : VL2
      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              : VL2
      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
 
      Instrument Host ID              : VL2
      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/VL2-M-MET-4-BINNED-P-T-V-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 were noted shortly before launch.  The readings exhibited a
      temperature-dependent error, increasing as Lander body
      temperature decreased.  The error gradually decreased after
      power-up of the electronics, approaching a steady-state value
      after 30-40 minutes of operation.  Analysis of the landed data
      and comparison with the reference temperature sensors on both
      Landers (see below) and the ambient temperature sensor on
      Lander 1 permitted a suitable correction to be applied.  This
      required that power be left on continuously to eliminate drift.
      This was done from Lander 2 sol 25 onward.  The corrections to
      the Lander 2 ambient temperature sensor limit its accuracy to
      about 3 degrees Celsius (see HESS_ETAL_1977).
 
      The reference temperature sensor was a platinum resistance
      thermometer mounted between the wind speed elements (see
      below).  It was susceptible to radiation and conduction errors
      and the effects of the thermal plume of the wind sensor
      assembly, but corrections for these have been applied.  The
      residual error is believed to be less than 4 degrees
      Celsius.(see HESS_ETAL_1977).
 
      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 the 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) precludes unambiguous determination of wind
      direction without modification to the analysis techniques and
      software used to generate this data set (see HESS_ETAL_1977);
      therefore, this data set does not include Lander 1 measurements
      made after sol 45.  A data set which has recovered a period of
      measurements made between Lander 1 sol 1 and 350 is available;
      refer to PDS data set id VL1-M-MET-4-BINNED-P-T-V-CORR-V1.0.
 
      The data set contains the following fields related to
      confidence level (listed as the field name followed by a
 
      PRESS_FLAG
       Warning flags concerning binned pressure values with
       missing data, no data, lander interference, and
       splined values
 
      WIND_FLG
       Warning flags concerning binned wind values with missing
       data, no data, lander interference, and splined values
 
      T_NLI_FLAG
       Warning flags concerning binned temperature values
       (no Lander interference) with missing data, no data,
       and splined values
 
      TAMB_INT_MN
       The mean Lander interference effect on the ambient
       temperature in each bin
 
      TAMB_INT_DEV
       The standard deviation of Lander interference effect
       on the ambient temperature in each bin
 
      TREF_INT_MN
       The mean Lander interference effect on the reference
       temperature in each bin
 
      TREF_INT_DEV
       The standard deviation of Lander interference effect
       on the reference temperature in each bin
 
      T_INT_FLAG
       Warning flags concerning Lander interference effects
       on temperature values with missing data, no data,
       and splined values