Data Set Overview
    =================

      The dataset comprises four file types,  namely summary and raw for High
      Rate and Event Mode data respectively.  The raw files allow close
      examination of the signal for individual events, whereas the summary
      files are intended as an index (to identify occasions where signals are
      anomalous) and for large-scale correlations.

    Parameters
    ==========

      The raw files, as comma-separated values extracted from an archive at
      University of Texas (the 'VUSA tapes', Viking Unscrambled Seismic
      ASCII), each comprise the data from the entire mission in a single
      axis (e.g. X-axis corresponds to the vertical sensor).  Each line in
      the file corresponds to a single raw record, which (due to the memory
      in the instrument) corresponds to 51 samples in Event (i.e. approx 51
      seconds long) or 83 samples (just over 4 seconds) in High rate mode.
      These readings are preceded by record number and acquisition time
      information (Sol, hour, minute, second) reconstructed from the lander
      clock. For the High rate data files, the readings are the
      instantaneous velocity signal in the relevant axis.  For event mode
      data, the readings are either the amplitude or the frequency (a
      separate file for each).
      
      The summary files present statistics of each High or Event mode record
      -  mean, deviation, maximum value etc., together with the nearest
      available meteorology readings.  The record number at the start of
      each summary record allows the corresponding raw record to be readily
      identified.  Additionally, the estimated time between the nearest
      meteorology data and the seismic record is noted - to allow filtering
      of only those occasions where the data were near-simultaneous, for
      example.   Note that uncertainties in the relative time
      reconstruction (performed differently on the seismometer and
      meteorology instruments) may be as high as 100 seconds.

      Times are specified in Local Lander Time, where Sol 0 was landing sol. 
      Landing occurred at  22:58:20 UT (9:49:05 a.m. local Mars time) on 
      September 3, 1976. Note that the time in the record corresponds to the 
      end of the record.

      Wind azimuths are directions towards which the wind is blowing, 
      measured clockwise from north; thus 90 degrees is Eastwards.

      The instrument is a velocity-sensing instrument, and thus the 
      displacement to which a given reading corresponds is frequency-
      dependent, and depends on filter settings and gain states which have 
      not been recovered. In general the highest sensitivity settings were 
      used, and one digital data unit (DU) corresponds to 2 nm of 
      displacement at 3 Hz or 10nm at 1 Hz - see [ANDERSONETAL1977] where 
      fuller details are given, note especially fig.6 in that paper. The 
      response is also slightly dependent on the choice of event 
      vs high rate mode. 

    Processing
    ==========

      In the processing of the VUSA data, a small number of corrupted
      records were simply rejected. Thus a purely ordinal comparison of
      these PDS archive files with VUSA data should allow for a skipped
      entry.  The VUSA line number indicated in the PDS summary record
      provides the correct location, however. Because the VUSA tapes may 
      include multiple playbacks, occasional duplicate records may appear.
      
      The raw files report the readings or zero crossings as integers, which
      are simply reproduced, together with the reconstructed acquisition
      time.
      
      The summary files indicate an ordinal record number (identifying the
      corresponding raw record in the raw files) the acquisition time in 
      decimal sols, as well as the original VUSA location (file, line number)
      followed by the first X-axis value in that record, the maximum and
      minimum X-values, then the rms variation in each axis (multiplied by
      100) and the mean number of X,Y,Z zero crossings indicating
      frequency.  These are then followed by the mission time in decimal
      sols corresponding to the meteorology datapoint acquired closest in
	 time, and the meteorology data itself and the time difference between
      the start of the seismic record and the meteorology reading.  
      
      The meteorology data were provided by J. Murphy of New Mexico State
      University, and comprise wind speed, direction, pressure and air 
	 temperature data. 
      
    Data
    ====

      Event mode data in fact comprise the largest fraction of the archive
      (256,087 records, against 47,361 High rate records). Event data were
      acquired for much of the day during the first ~60 sols, and in the
      night hours (~20-23 hrs until ~3 hrs) for most of the mission. 
      
    Naming Conventions
    ==================

      The raw files are named vpds_MMMM_ATYP.CSV  where MMMM is event or
      high, A is the axis (X,Y,Z) and TYP is DAT (for High rate mode, the
      raw velocity readings), or for Event mode, AMP or FREQ for the 
      envelope amplitude or frequency. 
      
      The summary files are EVENT_WIND_SUMMARY.TAB and HIGH_WIND_SUMMARY.TAB
      respectively.

Overview
    ========

      The data are believed to be generally of good quality, but is dominated
      by wind-generated signals [e.g. NAKAMURA&ANDERSO1979].
      
      Users should consult [ANDERSONETAL1976, ANDERSONETAL1977] to ensure
      familiarity with the instrument, operations and the character of wind
      noise and calibration signals etc. 
    
    Review
    ======
    
      This archive has passed a peer review according to PDS requirements.

    Data Coverage and Quality
    =========================

      Data coverage is summarized in [LORENZ&NAKAMURA2014]. In brief, due to
      data limitations (of storage on the lander, as well as the overall
      downlink data rate) High rate data were acquired relatively
      sporadically. A number of sessions were performed in early mission
      (Sols 30-60).  Brief sessions of early morning data (~2 or 3 hrs local
      time, where wind noise was at a minimum) were obtained throughout the
      mission.
      
      Normal mode data were acquired for much of the day for much of the
      mission but are of very limited utility.
      
      The data include lander disturbances as well as wind noise,
      calibration signals, and (perhaps) real seismic events.  These lander
      disturbances include documented activities (operation of the sampling
      arm, and the agitator of the X-ray fluorescence experiment - these are
      documented in [MOOREETAL1987] and [BAIRDETAL1977] respectively).
      Additional disturbances result from slewing of the S-band
      telecommunications antenna, and operations of the camera and lander
      tape recorder. Some electrical noise is also suspected in the record,
      due to switching of heaters in the lander meteorological
      instumentation, and thermal 'pops' of the lander occur, up to 25 per
      day [ANDERSONETAL1976]. 
      
    Limitations
    ===========

      Because of the timing uncertainties, 1:1 correlation of meteorology
      and seismic data should be performed with caution. Offsets of a few
      tens of seconds may be possible.