Data Set Overview
  =================
    The APXS_oxides is a listing of weight percent oxide abundances
    derived from the X-ray portion of the APXS_EDR data from the
    Alpha Proton X-ray Spectrometer (APXS).  This data is preliminary
    and will be later refined as new calibration data become
    available.  Currently, there are oxide results for five rocks and
    six soils.
 
    Geochemists usually express the abudance of elements in rocks and
    minerals as weight percents of the oxides.  It is a convenience
    that is followed because most rock forming minerals are
    stoichiometric compounds and it makes comparison and calculations
    easier.  It does not mean that those specific oxides are
    necessarily found as minerals or compounds in the sample
    analyzed; it is only a way to recast the element abundances.  Nor
    does it mean that Fe in the sample is 2+ rather than 3+.  It is
    simply a way of expressing the chemical abundances by
    stoichiometric assignment to oxides.  For geochemical
    convenience, we have recast the Pathfinder APXS elemental
    abundances of Na, Mg, Al, Si, S, K, Ca, Ti, Fe, and Cl to weight
    percent Na2O, MgO, Al2O3, SiO2, SO3, K2O, CaO, TiO2, FeO and Cl.
 
    Futher calibration is necessary to determine oxide abundances for
    the one other soil and four other rock measurements obtained at
    the Pathfinder landing site.  The APXS bumper ring did not make
    good contact with the soil during A-9 measurements, so more
    testing is needed to determine the uncertainties on the oxides
    for this.  The X-ray spectra for A-19, A-20, A-23, and A-27 rock
    measurements were degraded due to the rover battery death on Sol
    56.  The APXS_EDR data for these are available now, and oxide
    abundances will be determined at a later date.
 
 
  Parameters
  ==========
    The parameters are (1) weight percent abundances of chlorine and
    the oxides: Na2O, MgO, Al2O3, SiO2, SO3, K2O, CaO, TiO2, and FeO;
    (2) uncertainties on those abundances; and (3) the original sum
    of the oxides before normalization.  The original sum varies in
    response to the measurement geometry and is closer to 100% if
    good contact is made between the sample and the APXS bumper ring.
 
 
  Processing
  ==========
    The only input necessary for processing was APXS EDR data.  These
    data files were the cumulative sums of data acquired from the
    beginning of the measurement cycle until the final reading.
    Readings occurred several times for each rock and soil that was
    analyzed.  The first step in processing the data is to subtract
    subsequent spectra from one another and examine the deconvolved
    spectra to check for the possibility of any damaged data or
    instrument drift (e.g.  by changing environmental temperature).
    The next step is to establish any changes in energy calibration,
    mainly due to changes in environmental temperature and shift the
    data to correct gain and zero-offset drift.  Then the individual
    shifted spectra are summed together.  The summed composite go
    into a least-squares fitting program that subtracts the
    background, finds all the peaks in the spectra, and calculates
    the peak areas and their uncertainties.  Calibration curves (peak
    area versus concentration) for each element are used to derive
    abudances of each element.  These calibration curves were
    obtained by analyzing terrestrial samples of known composition
    during the APXS calibration in the laboratory.  Some corrections
    for matrix effects for a few of the elements are made after this.
    Then, to express the element abundances as oxide abundances,
    oxygen is assigned stoichiometrically (Fe as FeO, S as SO3, etc.)
    and the analyses are renormalized to an arbitrary value, in this
    case 98.0%.  P2O5, Cr2O3, and MnO are not included in these
    preliminary results because they have large errors and the final
    calibration for these has not been completed.
 
 
  Data
  ====
    All of the data in this dataset are contained in an ASCII tabular
    file, ('OX_PERC.TAB') with a detached PDS label ('OX_PERC.LBL').
 
    The tabular file is formatted so that it may be read directly
    into many database management systems (DBMS) or spreadsheet
    programs on various computers.  All fields in the table are
    separated by commas; text fields are left justified and numeric
    fields are right justified.  The 'start byte' and 'bytes' values
    listed in the PDS label do not include the commas between fields.
    The records are of fixed length, and the last two bytes of each
    record contain the ASCII carriage return and line feed
    characters.  This allows the table to be treated as a fixed
    length record file on computers that support this file type and
    as a normal text file on other computers.
 
    The PDS label is object-oriented.  The object to which the label
    refers (the TABLE) is denoted by a statement of the form:
 
        ^object = location
 
    in which the carat character ('^', also called a pointer in this
    context) indicates that the object starts at the given location.
    For an object located outside the label file (as in this case),
    the location denotes the name of the file containing the object.
    For example:
 
        ^TABLE = 'OX_PERC.TAB'
 
    indicates that the TABLE object is in the file OX_PERC.TAB, in
    the same directory as the detached label file.
 
    The detached label file is a stream format file, with a carriage
    return (ASCII 13) and a line feed character (ASCII 10) at the end
    of each record.  This allows the file to be read by the MacOS,
    DOS, Unix, and VMS operating systems.
 
 
  Ancillary Data
  ==============
    Calibration APXS measurements obtained in the laboratory.
 
 
  Coordinate Systems
  ==================
    Estimates of the locations of the 5-cm diameter spots measured on
    rocks and soils on Mars are reported as XYZ coordinates in the
    Martian Local Level Coordinate Frame.  Only those for which the
    oxide abudances have been determined are listed:
 
    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-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
 
    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
    APXDDRDS.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 oxides data can be displayed on UNIX, Macintosh, and PC
    platforms using any ASCII editor.
 
 
  Media / Format
  ==============
    The APXS oxides 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.