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