Overview:
    =========

    The Neutral Particle Imager (NPI) measures integral ENA fluxes
    in the energy range 0.1 to 60 keV to help satisfy the following
    scientific objectives:

       1. Determine the instantaneous global distributions of plasma
          and neutral gas near Mars

       2. Energy deposition from the solar wind to the ionosphere

       3. Search for the solar wind-Phobos interactions

    Parameters:
    ===========

    All NPI data products have the same format and parameters, and
    each row (data file record) in the NPI SPREADSHEET data products
    has eight (8) COLUMN objects (parameters):
       1. Start Time - Begin Date/Time in UTC of data samples
       2. Stop Time - Ending Date/Time in UTC of data samples
       3. Data Type Name - either SENSOR or MODE. The SENSOR rows are
          the NPI science data for each sector (32 sectors). The MODE
          rows contains informational data like Accumulation Time and
          MCP Mode.
       4. Data Type Id - Numeric ID indicating either SENSOR or MODE.
       5. Data Name - Short description for data on that row.  For
          example 'Sector 0' for NPI sector 0 science data (SENSOR
          row), or 'Accumulation Time' for informational data (MODE
          row).
       6. Data Unit - Indicates the data unit (c/sec for SENSOR data,
          unitless for MODE data).
       7. Values - These are the actual data values.  For NPI, there
          is one value per row (sector).
       8. Data Quality Value - Quality indicator for the data on that
          row. See CONFIDENCE_LEVEL_NOTE under 'Data
          Coverage/Quality' for valid
          values and descriptions.

    Data Products:
    ==============

    The only Standard Data Product for the combined NPI PSA Level 1b
    (EDR) / PSA Level 2 (RDR) is:

       1. NPINORM_C_SEC - Neutral Particle Imager NORMal mode data in
          Counts / SECond (count rate).

    Ancillary Data:
    ===============

    It is important for ASPERA-3 science studies to know where in
    space and time the Mars Express spacecraft and ASPERA-3
    instruments are located and what objects (Sun, Mars, Earth,
    Phobos, Deimos) are in the fields of views. The ASPERA-3 view
    directions for each sensor can be derived using the SPICE kernels
    and software. The ASPERA-3 Sensor Frames and Geometry Information
    document (in DOCUMENT directory) provides a code example (in C
    and FORTRAN) for determining the view directions for the ASPERA-3
    sensors.

    Coordinate System:
    ==================

    The ASPERA-3 data are always in the instrument reference frame
    since data are sampled in situ. The GEOMETRY table contains
    spacecraft related parameters expressed in the J2000 reference
    frame, and the ASPERA-3 Sensor Frames and Geometry Information
    document (in DOCUMENT directory) provides information for
    determining the ASPERA-3 sensors view directions and transforming
    to the J2000 reference frame.

    References:
    ===========

    Refer to the ASPERA-3 Experiment to Archive Interface Control
    Document (EAICD) found in the DOCUMENT directory
    (MEX_ASPERA3_PSA_ICD_V02_01) for more information and detail
    concerning data set formulation and contents.

Review:
    =======

    These data have been reviewed by the instrument team and are of
    the highest quality that can be generated at this time. Science
    results based on these data have been published in several
    journals (Science, Nature, EGU, etc.). After submission to the
    PDS, these data successfully completed the peer review process.

    Data Coverage/Quality:
    ======================

    The data quality indicators in the data files for each sensor are
    associated with the data returned in telemetry.  Valid values
    are:

       0 - Good Data: Default because assumption is that data
                      are good unless determined otherwise.

       1 - Questionable Data: +30V monitor value is not within
                              tolerance

       2 - Invalid Data: +12V, +5V, or -5V monitor value is not
                         within tolerance

       3 - Bad Data: +30V monitor value and (+12V, +5V, or -5V
                     monitor value) are not within tolerance

       4 - Unknown State: Time related Main Unit housekeeping packet
                          is not available.

      -1 - Data Unavailable:  No data returned for the sensor, so a
                              fill value is used for data quality.

    Limitations:
    ============

       There are no known limitations at this time.