Data Set Information
DATA_SET_NAME VL1/VL2 MARS METEOROLOGY RESAMPLED DAILY AVG PRESSURE V1.0
DATA_SET_ID VL1/VL2-M-MET-4-DAILY-AVG-PRESSURE-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION Data Set Overview : This data set contains summary pressure data obtained from the Viking Meteorology Instrument System (VMIS) through the duration of the Viking Lander 1 and 2 missions. The data are derived from the ambient pressure sensor carried onboard the Landers. The data set consists of the daily average pressure values and relevant statistics presented on a sol by sol basis. For further background information on the VMIS and results from this experiment, see CHAMBERLAIN_ETAL1976, HESS_ETAL_1977, TILLMAN_ETAL_1979, HESS_ETAL_1980, and SHARMAN_RYAN_1980. An earlier version of this data set, including descriptive documents and plots on microfiche, is archived at the NSSDC (NSSDC ID 75-075C-07I, 75-075C-07J, 75-083C-07I, and 75-083C-07J). 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 beginning of each local day (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 PRESS_MEAN Daily average atmospheric pressure PRESS_MIN Minimum daily atmospheric pressure PRESS_RANGE Maximum variation in pressure during each day PRESS_SIGMA Standard deviation in the daily average pressure 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 BIT_ERR_RATE Indicates quality of spacecraft to ground communications WARNING_FLAG Flags indicating number and length of time gaps Processing Level Id : 4 Software Flag : Y Processing Start Time : UNK Processing Stop Time : UNK Native Start Time : 97.1 AREOCENTRIC SOL LON, EARTH YR 1976 Native Stop Time : 226.7 AREOCENTRIC SOL LON, EARTH YR 1982 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 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 : 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 : VL1/VL2-M-MET-3-P-V1.0 Software : UNK Product Data Set ID : VL1/VL2-M-MET-4-DAILY-AVG-PRESSURE-V1.0
DATA_SET_RELEASE_DATE 1989-11-01T00:00:00.000Z
START_TIME 1976-07-20T12:00:00.000Z
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 VIKING METEOROLOGY INSTRUMENT SYSTEM
INSTRUMENT_ID MET
INSTRUMENT_TYPE METEOROLOGY
NODE_NAME Planetary Atmospheres
ARCHIVE_STATUS ARCHIVED
CONFIDENCE_LEVEL_NOTE 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. The pressure measurements were digitized into 255 approximately equal increments (digital numbers or DNs), giving a basic pressure digitization interval of 0.088 millibars. Raw DNs between 0 and 255 were converted to pressures by linear interpolation between calibration points. Due to the limited pressure range on Mars, the only calibration points used are those for DNs 100, 120, and 160. DN 140 was left out of the calibration table, producing a maximum error of 0.0425 millibar for VL1 and 0.008 millibar for VL2; corrections have been applied to the data set to correct for this missing calibration point. As the output of the pressure transducer is quantized in 0.088 millibar increments, the resolution of a single measurement is limited to 0.088 millibar. On average, half of the measurements producing a given pressure value are at least one half a quantum above the indicated value and that value is actually the lower bound of the actual value. By adding 0.044 millibar to each measurement, any estimate of the average pressure (generally having greater resolution than one DN) will not be biased (see HESS_ETAL_1980). Such accuracy is important as features of the annual pressure cycle repeat within 0.02 millibar or less and it is important to establish the actual value for comparison between years and for future missions to Mars. The pressure measurements are presented in the form of sol averages and sol range. 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 pressure on each sol. With sampling intervals of less than approximately two hours, the average very closely approximates the true average. 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. Since the pressure quantization is 0.088 millibar, the daily range has discrete jumps and fluctuates by one quantum. Gaps in the data indicate missing sols or sols for which the sampling is too infrequent to obtain a meaningful value. In addition, bit error rate information is tabulated on a sol by sol basis so that errors on the communication link can be quantified. The data set contains the following fields related to confidence level (listed as the field name followed by a 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 BIT_ERR_RATE Indicates quality of spacecraft to ground communications WARNING_FLAG Flags indicating number and length of time gaps
CITATION_DESCRIPTION Citation TBD
ABSTRACT_TEXT This data set contains summary pressure data obtained from the Viking Meteorology Instrument System (VMIS) through the duration of the Viking Lander 1 and 2 missions. The data are derived from the ambient pressure sensor carried onboard the Landers. The data set consists of the daily average pressure values and relevant statistics presented on a sol by sol basis. For further background information on the VMIS and results from this experiment, see CHAMBERLAIN_ETAL1976, HESS_ETAL_1977, TILLMAN_ETAL_1979, HESS_ETAL_1980, and SHARMAN_RYAN_1980. An earlier version of this data set, including descriptive documents and plots on microfiche, is archived at the NSSDC (NSSDC ID 75-075C-07I, 75-075C-07J, 75-083C-07I, and 75-083C-07J).
PRODUCER_FULL_NAME JAMES E. TILLMAN
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