Data Set Information
DATA_SET_NAME VL1/VL2 MARS METEOROLOGY CALIBRATED FOOTPAD TEMP V1.0
DATA_SET_ID VL1/VL2-M-FTS-3-FOOTPAD-TEMP-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : This data set contains the Martian near-surface temperatures obtained from the Viking Lander 1 and 2 thermocouple footpad temperature sensors. 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 VIKING_YEAR - Viking mission year, starting at 1 when the Viking spacecraft reached Mars, and incremented at Ls : 0 every martian year SOL_LON - Areocentric longitude of the sun corresponding to the local Martian time MARTIAN_DAY - Martian solar day (sol), starting at sol 0 when each Lander touched down. Each martian day is 24 hr 39 minutes 35.25 seconds in length. LOCAL_HOUR - Local hour: Earth hour LOCAL_MINUTE - Local minute: Earth minute LOCAL_SECOND - Local second: Earth second TEMP_FOOTPAD - Footpad temperature: degrees Kelvin 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 point by point data 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]). 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).
DATA_SET_RELEASE_DATE 1996-03-26T00:00:00.000Z
START_TIME 1979-05-22T12:00:00.000Z
STOP_TIME 1982-11-13T12:00:00.000Z
MISSION_NAME VIKING
MISSION_START_DATE 1975-08-20T12:00:00.000Z
MISSION_STOP_DATE 1983-02-01T12:00:00.000Z
TARGET_NAME MARS
TARGET_TYPE PLANET
INSTRUMENT_HOST_ID VL1
VL2
INSTRUMENT_NAME UNK - INSTRUMENT ID (FTS)
INSTRUMENT_ID FTS
INSTRUMENT_TYPE THERMOMETER
NODE_NAME Planetary Atmospheres
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE 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]. 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).
CITATION_DESCRIPTION TBD
ABSTRACT_TEXT not applicable
PRODUCER_FULL_NAME WILLIAM R. GUEST
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