Data Set Overview
  =================
    The APXS EDRs are a collection of 27 measurements (173 data
    files) obtained by the Alpha Proton X-ray Spectrometer (APXS).
    Of these, nine are measurements of rock, seven are of soil (if
    Scooby Doo is an indurated soil rather than a rock), and eleven
    are of atmosphere.  The atmosphere was measured on Sol 1 to
    determine background cosmic ray levels, on a few occasions for
    electronics noise tests, and sometimes as a result of the APXS
    deployment mechanism not reaching the intended rock surface.
 
    During the rover's 83 Sol mission on Mars, it nearly
    circumnavigated the lander, staying within a 12 meter radius of
    the lander.  Early APXS measurements were taken on rocks to the
    north of the lander (Barnacle Bill and Yogi) and a variety of
    soils near the end of the ramp and to the east of the end of the
    ramp (cloddy deposits between the ramp and Yogi, Scooby Doo,
    wheel-disturbed soil next to Scooby Doo, and soil next to Lamb).
 
    The unusually high sulfur content of the rock analyses for
    Barnacle Bill and Yogi indicated that the APXS may have sampled
    weathered rock or rock covered by sulfur-rich dust or soil, so
    the rover was sent towards the 'Rock Garden' for more rock APXS
    analyses.  This is an area to the southwest of the lander
    containing several large rocks, some of which have low red/blue
    ratios (less oxidized iron) and what appeared to be near-vertical
    rock faces (less likely to be heavily dust covered).  En route,
    an APXS measurement was taken on the 'dune-like' feature called
    Mermaid Dune.  The 'Rock Garden' terrain was difficult for rover
    driving and the loss of the rover battery on Sol 56 slowed down
    operations, but during the last 46 Sols, seven additional rock
    APXS analyses were obtained.  Two analyses were taken on one rock
    (Half Dome), although the rover battery was alive for the first
    one and dead for the second one.  Preliminary X-ray composition
    results for eleven APXS analyses (5 rocks and 6 soils) are given
    in [RIEDERETAL1997B].
 
    An inventory of the 173 APXS_EDR data files is found in a table
    provided in three formats: APXS_INV.HTM (HTML), APXS_INV.ASC
    (formatted ASCII text), and APXS_INV.TAB (comma separated value
    ASCII).  (The former two are found in the DOCUMENT directory on
    the MPRV_0001 CD, and the latter is in the INDEX directory of the
    same CD.) The inventory lists for each data file: APXS
    measurement number; rover command number; rover command sequence
    number; VICAR data file name; whether the file contains
    cumulative data, is the start of a new data collection, or is a
    re-read of old data from the memory; measurement start and stop
    times (in SCLK and Local True Solar Time); target; and
    measurement comments (including duplicate insurance readouts of
    the APXS memory, sequence requeue mistakes, electronics noise
    tests, and power problems).
 
 
  Parameters
  ==========
    During each measurement session four spectra are accumulated,
    each containing up to 256 channels.  Each channel consists of two
    bytes, organized as an event counter (each channel can contain a
    maximum of 65535 counts; the channel number corresponds to the
    amplitude of the event, i.e.  the energy of the registered
    particle/photon.  The first spectrum, called the 'alpha
    spectrum', contains events registered by the alpha detector only.
    The second spectrum, called the 'proton spectrum', contains
    events registered simultaneously by the alpha and the proton
    detector (the amplitude being the sum of the amplitude of both
    signals).  The third spectrum ('X-ray spectrum') contains events
    registered by the X-ray detector and the fourth spectrum
    ('background spectrum') contains events registered by the proton
    detector only.  This fourth spectrum is essentially cosmic ray
    background events.  Further details are provided in
    [RIEDERETAL1997A].
 
    Other parameters measured are the temperature of the X-ray
    preamplifier in the sensor head, the temperature of the alpha
    detector preamplifier in the rover's warm electronics box (in
    degrees Centigrade), and the sampling duration of the alpha,
    proton, and X-ray measurements (hh:mm:ss).
 
 
  Processing
  ==========
    The only processing performed on the data was Real Time
    processing, using the VICAR (Video Image Communication and
    Retrieval) program MPFTELEMPROC.  This program obtained the
    Standard Formatted Data Unit (SFDU) records from the Telemetry
    Delivery Subsystem (TDS), and reconstructed the data files (each
    of which contained 4 spectra) from the telemetry data.  The data
    files were compared to any previously downloaded versions to
    determine which contained the most data.  The versions with the
    greatest amount of data were retained.  The program resulted in
    VICAR formatted files with a subset of descriptive label items.
    The label information was then supplemented with data derived
    from the mission catalog and SPICE kernels.  Finally, each file
    was run through the VICAR program MPFPDSLBL to convert the labels
    to PDS format.
 
    The APXS Experiment Data Records were created at the Multimission
    Image Processing Laboratory of the Jet Propulsion Laboratory.
 
 
  Data
  ====
    The APXS EDR data are stored as image data files, each file
    containing four lines (four spectra) and 256 samples (256 16-bit
    unsigned numbers).
 
    Some data files are completely new starts, as indicated by
    ACCUMULATION_COUNT=1 in the file header, and these only contain
    temperature measurements at the beginning and end of the APXS
    measurement session.  Other files are 'cumulative spectra' and
    consist of accumulations of multiple measurement sessions added
    together, and the number of sessions is indicated by the
    accumulation count.  For cumulative spectra, temperatures at the
    beginning and end of each measurement session are recorded and
    counts for each detector are summed with those for previous
    accumulations.  Up to 10 accumulations are possible.
 
 
  Ancillary Data
  ==============
    Clock conversion software was taken from NAIF (Navigation and
    Ancillary Information Facility) software tools.  The most
    up-to-date spacecraft and instrument kernels available can be
    obtained from the anonymous FTP site of the Navigation and
    Ancillary Information Facility at JPL, ftp://naif.jpl.nasa.gov/.
    For further assistance, contact Boris Semenov of the PDS NAIF
    node:
 
    Address:     Boris Semenov
                 M/S 301-150
                 Jet Propulsion Laboratory
                 Pasadena, CA 91109-8099
 
    Phone:       (818) 354-8136
    Email:       Boris.V.Semenov@jpl.nasa.gov
    WWW URL:     http://pds.jpl.nasa.gov/naif.html
    FTP Site:    ftp://naif.jpl.nasa.gov/
 
 
  Coordinate System
  =================
    Estimates of the locations of the 5-cm diameter spots measured on
    rocks and soils on Mars are reported here as XYZ coordinates in
    the Martian Local Level Coordinate Frame:
 
    APXS
    meas.     X         Y        Z        Rock/Soil APXS Target
    -----    ----     -----    -----   ----------------------------
    A-2      1.89    -1.95     0.31    soil off the end of the ramp
    A-3      1.30    -2.45     0.18    Barnacle Bill rock
    A-4      2.79    -2.64     0.28    soil near Yogi
    A-5      3.29    -2.48     0.28    soil near Yogi
    A-7      4.58    -2.91    -0.18    Yogi rock
    A-8      2.85     1.13     0.32    Scooby Doo indurated soil or rock
    A-9      3.08     1.32     0.28    disturbed soil next to Scooby Doo
    A-10     3.74    -0.43     0.28    dark soil next to Lamb
    A-15    -5.87     2.80     0.52    Mermaid dune
    A-16    -3.79    -1.31     0.12    Wedge rock
    A-17    -5.56    -3.25    -0.35    Shark rock
    A-18    -4.81    -3.81    -0.54    Half Dome rock, first location
    A-19    -4.82    -4.13    -0.59    Half Dome rock, second location
    A-20    -4.20    -4.10    -0.38    Moe rock
    A-23    -3.48    -3.86    -0.43    Stimpy rock
    A-27    -9.03    -2.59    -0.07    Chimp rock
 
    The Mars Pathfinder Lander (L) Coordinate Frame
 
    The Mars Pathfinder Lander is a tetrahedral structure.  One of
    its faces, the one upon which it sits, is called the base petal
    and houses most of the lander equipment.  The other three faces,
    or petals, open after surface impact to expose these systems.
    The rover is mounted on one of these petals.  The Mars Pathfinder
    Lander Coordinate Frame, or 'L' Frame, has the lander base petal
    as its reference plane and its center coincident with the
    geometric center of the base petal.  The YL-axis of this
    coordinate system passes through the geometric center of the
    rover petal, and defines the reference direction.  The ZL-axis is
    normal to the reference plane and coincident with the nominal
    spacecraft spin vector.  When the lander is upright on the
    surface, the ZL-axis is directed positively downward into the
    ground.
 
    The Martian Local Level (M) Coordinate Frame
 
    The Martian Local Level Coordinate Frame is a right handed,
    orthogonal, frame whose origin is co-incident with the origin of
    the Lander Coordinate Frame.  The XM axis points north, the YM
    axis points east, and the ZM axis points down.
 
    For more information on Mars Pathfinder coordinate systems, see
    the [MELLSTROM&LAU1996], [WELLMAN1996B], and [VAUGHAN1995]
    references.  However, please note that as of the time this
    APXEDRDS.CAT file was written, [WELLMAN1996B] had not yet updated
    his discussion of elevation measurements to match that agreed
    upon by the Project.  Where he used elevation ranges of 0 to 180
    degrees, the MPF Project used -90 to +90 degrees.
 
 
  Software
  ========
    The APXS data can be displayed on UNIX, Macintosh, and PC
    platforms using the PDS developed program, NASAView.  This
    software is freely available from the PDS Central Node and may be
    obtained from their web site at http://pds.jpl.nasa.gov/.  For
    more information or help in obtaining the software, contact the
    PDS operator at the following address:
 
    Address:     Planetary Data System, PDS Operator
                 Jet Propulsion Laboratory
                 4800 Oak Grove Drive
                 Pasadena, CA 91109
 
    Phone:       (818) 354-4321
    Email:       pds_operator@jpl.nasa.gov
    WWW URL:     http://pds.jpl.nasa.gov/
 
 
  Media / Format
  ==============
    The APXS EDR data will be stored on compact disc-read only memory
    (CD-ROM) media.  The CDs will be formatted according to ISO-9660
    and PDS standards.  The data files will not include extended
    attribute records (XARs), and will therefore not be readable on
    some older VMS operating systems.

Confidence Level Overview
  =========================
    The Alpha Proton X-ray Spectrometer (APXS) functioned well during
    the 83 sols of operation on the Martian surface.  For nighttime
    X-ray measurements, a temperature variation of more than 100
    degrees C during the data accumulation produced a shift in peak
    position smaller than a fraction of an energy channel.
 
 
  Review
  ======
    Prior to release, the data will be reviewed by the APXS
    instrument team and the Planetary Data System.
 
 
  Data Coverage and Quality
  =========================
    The highest quality measurements for soils were A-4, A-5, A-8,
    A-10, and A-15.  The highest quality measurements for rocks were
    A-3, A-7, A-16, A-17, and A-18.  The preliminary X-ray results
    for all of these high quality measurements are shown in
    [RIEDERETAL1997B].  Results for the soils A-2 and A-9 are not as
    good, due to poor contact with the sample by the APXS deployment
    mechanism and lower counting rates for alpha particles, protons,
    and X-rays.  The rover battery died in the early morning of Sol
    56, and all further APXS measurements had to be made during the
    daytime, which had an adverse affect on the X-ray portion of the
    data for rock measurements A-19, A-20, A-23, and A-27.  These
    four suffer from increased noise and low counting rates in the
    X-ray spectra (especially adverse for the low energy events and
    low atomic number elements such as sodium), but the alpha and
    proton portions of the data retain high quality.  Some of the
    files after Sol 55 have defects, with proton, or X-ray data not
    always appearing in the same file, and the time placed at the
    start of the data stream is incorrect.
 
    When measuring rock and soil samples, the desire was to obtain at
    least 10 integrated hours.  Only 3 hours of nighttime measurement
    were needed for a good X-ray analysis.  X-ray spectra obtained
    during the night, when ambient surface temperatures were low,
    were unaffected by electronics noise.  Ten hours of measurement
    during the day or night provide good alpha and proton analyses.
    Shorter times still provide useful results.  Actual spectral
    accumulation times (listed in the table below) for the rock and
    soil analyses on Mars range from 5 to 16 hours.
 
    A summary of the 27 APXS measurements is shown in the table
    below.
 
    APXS    Measurement initial start  Integrated  APXS spectra
    meas.   time and final stop time   meas. time  accumulation
    number  (Local True Solar Time)      (hrs)      time (hrs)   Target
    -----   -------------------------  ----------  ------------  ------
    A-1     Sol 1 07:17 - Sol 2 09:58      2.8        1.9        atmos.
    A-2     Sol 2 14:53 - Sol 3 10:00     19.6       15.9        soil
    A-3     Sol 3 15:00 - Sol 4 07:01     16.5       13.6        rock
    A-4     Sol 4 16:59 - Sol 5 01:32      8.8        8.1        soil
    A-5     Sol 5 16:01 - Sol 6 06:55     15.3        9.2        soil
    A-6     Sol 10 09:01 - Sol 10 09:40    0.7        0.1        atmos.
    A-7     Sol 10 14:17 - Sol 11 02:37   12.7        5.7        rock
    A-8     Sol 14 14:03 - Sol 15 02:55   13.2        5.7        soil
    A-9     Sol 15 14:04 - Sol 16 03:15    8.6        7.7        soil
    A-10    Sol 20 14:03 - Sol 21 02:59    8.3        7.0        soil
    A-11    Sol 22 15:23 - Sol 23 02:40   11.6        4.8        atmos.
    A-12    Sol 24 17:07 - Sol 24 17:17    0.2        0.1        atmos.
    A-13    Sol 24 18:01 - Sol 24 18:12    0.2        0.1        atmos.
    A-14    Sol 25 00:06 - Sol 25 00:16    0.2        0.1        atmos.
    A-15    Sol 28 14:05 - Sol 29 02:44    8.0        5.3        soil
    A-16    Sol 37 14:07 - Sol 38 03:05    8.2        6.5        rock
    A-17    Sol 52 14:18 - Sol 53 03:05    8.0        7.0        rock
    A-18    Sol 55 14:06 - Sol 56 00:05    7.2        5.9        rock
    A-19    Sol 58 12:08 - Sol 64 10:45   12.6        8.9        rock
    A-20    Sol 64 12:04 - Sol 66 10:40   10.3        6.5        rock
    A-21    Sol 66 12:04 - Sol 67 10:32    5.2        3.0        atmos.
    A-22    Sol 67 12:04 - Sol 68 09:32    4.0        2.0        atmos.
    A-23    Sol 68 12:05 - Sol 70 10:47    9.5        4.9        rock
    A-24    Sol 76 12:09 - Sol 77 09:06    2.7        0.5        atmos.
    A-25    Sol 77 12:08 - Sol 78 09:06    3.0        0.8        atmos.
    A-26    Sol 78 12:03 - Sol 79 10:17    4.6        2.6        atmos.
    A-27    Sol 79 12:08 - Sol 82 09:47   11.1        6.3        rock
 
    Measurement initial start and stop times were obtained from the
    SCLK times in the downlink telemetry for the acknowledgement of
    the exact commands that were issued to trigger the start and stop
    of each APXS measurement (usually Meas_Start, Meas_Stop, Reset,
    or Shutdown).  SCLK times were converted to Local True Solar Time
    using the script sclk2ltmst (see Ancillary Data discussion).
    This time is only as accurate as the rover's clock, and is a
    close approximation to the exact initial start and stop time of
    each APXS measurement.  In a few cases, the downlink was lost,
    and uplink predictions were used instead.  Some of the cumulative
    APXS measurements were interrupted by other rover activities, in
    which case, the first accumulation start time and last stop time
    are indicated.  Integrated measurement time, as indicated by
    ALPHA_SAMPLING_DURATION, PROTON_SAMPLING_DURATION, and
    XRAY_SAMPLING_DURATION in the data file headers, is always less
    than the accumulation final stop time minus the initial start
    time, because the sampling durations do not include quiet periods
    when the APXS was powered off and detector 'dead time.'
 
    In 15 of the APXS_EDR files, the APXS spectra are filled with
    zeros.  This is the case when rover command sequence 50520D was
    requeued by mistake on Sol 6, when there was not enough power to
    turn on the APXS (some of the A-19 measurements).  The files
    filled with zeroes are indicated by N/A listings for measurement
    start and stop times in the inventory table of the 173 APXS_EDR
    data files (mentioned in the Data Set Overview).
 
 
  Limitations
  ===========
    Further calibration and special processing is needed to further
    reduce the APXS_EDR data and convert the alpha, proton, X-ray,
    and background spectra to elemental abundances.
 
 
  Time-Tagging
  ============
    In each APXS data file header, the PACKET_CREATION_SCLK is the
    time at which the rover formatted the packet for delivery to the
    lander.  In most cases, this is just a few seconds after the APXS
    measurement was actually completed.  Sometimes, though, it was
    much later, and this can be discovered by examining the inventory
    table of the 173 APXS_EDR data files (mentioned in the Data Set
    Overview).  The situations that resulted in longer time
    discrepancies were: (1) duplicate insurance readouts of
    previously read out data were often commanded on the morning
    following a series of nighttime readouts just in case the
    previous one was lost in transmission (these are indicated in the
    comments section of the inventory table), (2) re-reads of old
    data to recover from lander telemetry data that was lost but
    still held in the APXS memory (the A-19 files indicated as
    'reread of memory'), and (3) problems with rover power resulting
    in shutdown of the rover before APXS measurements had ceased
    (several A-2 files: commands 2749, 2762, 2775, and 3020 and one
    A-19 file: command 6138).
 
    One known discrepancy was found in the APXS time stamps, for A-2
    rover command 2723.  The ALPHA_SAMPLING_DURATION (and PROTON and
    XRAY) indicate a minimum duration between measurement start and
    stop time of 2 hrs 45 minutes, but the stop minus start time
    duration, as indicated by rover time stamps is 2 hrs 10 minutes.
    The cause of this discrepancy is unknown.
 
    In addition, the rover clock was sometimes significantly in error
    when it wasn't synced up with the lander clock beforehand.
    Syncing usually occurred early each morning.  The only way to
    check for this is to carefully examine the rover downlink
    telemetry.  Timestamps for A-19 are the most uncertain of the
    APXS files, because the rover battery stopped working early in
    the morning of Sol 56 and the rover had difficulty powering back
    up in the first few days following this event.