Data Set Overview : This data set contains sol averages of the Martian near-surface temperatures obtained from the Viking Lander 1 and 2 thermocouple footpad temperature sensors. The data set consists of the daily average footpad temperature values and relevant statistics presented on a sol by sol basis. The data set is composed of the following parameter fields (listed as the field name followed by a description).   Parameters : SC_ID Spacecraft id: VL1 : Viking Lander 1 VL2 : Viking Lander 2  SOL_LON Areocentric longitude of the Sun (Ls) corresponding to local midnight at the beginning of the sol  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. Each martian day is 24 hr 39 minutes 35.25 seconds in length.  T_FTPD_MEAN Daily average footpad temperature (degrees Kelvin)  T_FTPD_MIN Minimum daily footpad temperature (degrees Kelvin)  T_FTPD_RANGE Maximum variation in footpad temperature during each day (degrees Kelvin)  T_FTPD_SIGMA Standard deviation of the point-by-point footpad measurements from which the sol averaged value was determined (degrees Kelvin)  MAX_TIME_GAP Length of maximum time gap between two measurements (hours)  BEG_GAP_HOUR Local hour of maximum time gap start  BEG_GAP_MIN Local minute of maximum time gap start  BEG_GAP_SEC Local second of maximum time gap start  END_GAP_HOUR Local hour at which maximum time gap ended  END_GAP_MIN Local minute at which maximum time gap ended  END_GAP_SEC Local second at which maximum time gap ended  WARNING_FLAG Flags indicating number and length of time gaps, possible values are: .I - one or more time gaps of 3 hours or more, .C - a cross-midnight gap of 4 hours or more, IC - both .I and .C conditions, BB - no warning.  Note: For the temperature and time parameters, negative numbers are used to represent no recorded values on those sols.   Sensor Description : The footpad sensors, mounted on footpad 2 of each lander, are rugged thermocouples designed for measurements during atmospheric entry for engineering and the Entry Science Experiment [SEIFF1976]. They have served as a simple indicator of the surface, or near-surface, temperature during the mission [TILLMAN1985]. They were not designed to make good measurements of atmospheric temperature after landing, since their exposure, size, and location makes them susceptible to large conduction and radiation errors. Their relatively large radiation and conduction errors, their exposure to winds disturbed by the footpad and lander, and changes in the shadows of the lander with season and location, make it difficult to correct these radiation errors. At VL-1, the footpad sensor was buried by soil while for VL-2, it was free within the footpad. Details of the burial and exposure are given in [MOOREETAL1987].   Processing : The footpad temperature measurement is incorporated in the engineering data stream. Measurements are taken along with all other data in the same lander data format and the formats were sampled to satisfy both engineering and science requirements. For example, each meteorology data frame was associated with a prior and subsequent engineering frame to provide an atmospheric pressure measurement for the meteorology experiment - the pressure sensor was sampled by the engineering data system, not the Viking Meteorology Instrument System. Engineering and meteorology sampling requirements produced data frames at intervals from much less than one second to approximately 40 minutes.  The original point by point data (see PDS data set name VL1/VL2 MARS METEOROLOGY CALIBRATED FOOTPAD TEMP V1.0; data set id VL1/VL2-M-FTS-3-FOOTPAD-TEMP-V1.0) were edited to remove communications generated errors using automated procedures to reject bad points. These procedures checked against seasonally varying limit files and rejected points outside the limits. During the processing, these limits were updated for each lander and year. After the automated editing, the measurements were plotted, and remaining errors removed. The editing is similar to that of the Viking Lander pressure record (see PDS data set name VL1/VL2 MARS METEOROLOGY DATA CALIBRATED DATA PRESSURE V1.0; data set id VL1/VL2-M-MET-3-P-V1.0, and description in [NSSDC1993]).  The sol averages and ranges are calculated from this point-by- point data set. The sol average is obtained by weighting each measurement according to the period that it represents. The sol range is determined by subtracting the minimum from the maximum temperature on each sol. Each sol is checked for the maximum period between samples and when this value exceeds approximately three hours, the raw data are manually edited. The editing determines the validity of the data for each of the several functions which are separately flagged. For example, the data may be adequate to form a daily average but not a daily range.   Media/Format : This data set is sufficiently small that it is available online from the Planetary Atmospheres Node of the Planetary Data System (PDS), or from the National Space Science Data Center (NSSDC).

Confidence Level Overview : The footpad sensor was not designed to necessarily survive or provide low errors in the landed configuration footpad. It is larger in diameter than the meteorology sensor and therefore has a slower response time and is more subject to conduction and radiation errors, as well as air heated or cooled by some lander components. Since it is within the footpad and downwind of the lander for at least 120 degrees of wind direction, it is strongly influenced by the temperature of the lander leg, the footpad, and the lander. At times the lander shades it from direct sunlight and its long wave radiation to space is constrained by the lander. An example of the seasonal shading error can be seen in [TILLMAN1985] where the annual cycle of temperature is plotted as a function of time for several years. Due to the shading problems, there are two local peaks in the annual cycle instead of the expected single peak.  The footpad sensor is buried under the soil on VL-1 but not VL-2. [MOOREETAL1987] provide details of the exposure of the sensors. [SEIFF1976] states that the 'overall expected accuracy' in the descent phase is 1.25 degrees Kelvin. Comparing the design and exposure to the atmospheric sensor, it is expected that conduction and radiation errors of up to 10 degrees or more at low wind speeds are present in data from the VL-2 sensor. For VL-1, the base of the footpad is buried about .165 meters below the surface ([MOOREETAL1987], figures 16b, 88a, 88b), and only the top of the sensor housing is exposed. It appears that the thermocouples are buried well below the surface. Therefore, the temperature would be determined by the albedo, thermal conductivity of the soil and all of the associated lander physical parameters.  Regardless of these problems, the VL-1 footpad sensor gives a clear indication of major events on short time scales such as great dust storms, as shown by [TILLMAN1985].  The data set contains the following fields related to confidence level (listed as the field name followed by a description):  MAX_TIME_GAP Length of maximum time gap between two measurements (hours)  BEG_GAP_HOUR Local hour of maximum time gap start  BEG_GAP_MIN Local minute of maximum time gap start  BEG_GAP_SEC Local second of maximum time gap start  END_GAP_HOUR Local hour at which maximum time gap ended  END_GAP_MIN Local minute at which maximum time gap ended  END_GAP_SEC Local second at which maximum time gap ended  WARNING_FLAG Flags indicating number and length of time gaps   Data Coverage : Footpad temperature measurements were taken throughout the mission but were generated in edited and summarized format only after raw spacecraft mission data processing was implemented and formally begun by the Viking Computer Facility (VCF), Department of Atmospheric Sciences, University of Washington. These measurements from Viking Lander 1 were archived beginning at sol 1008 (May 22, 1979) and ending at sol 2245 (Nov. 13, 1982), the Lander's last downlink. For Viking Lander 2, data were archived beginning at VL2 sol 1000 and ending on sol 1050, which was the last high quality downlink. (Subsequent to sol 1050, there were unsuccessful attempts for about 100 sols to recover from a VL-2 power system failure).