Overview:
    =========

    The Ion Mass Analyzer (IMA) provides in situ ion measurements in
    the energy range 0.01 - 40 keV/q for the main ion components H+,
    He++, He+, O+, with 20-80 amu/q to help satisfy the following
    scientific objectives:

       1. Determine the instantaneous global distributions of plasma
          and neutral gas near Mars by providing undisturbed solar
          wind parameters

       2. Define the local characteristics of the main plasma regions

       3. Complement the ENA images

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

    All IMA data products have the same format and parameters, and
    each row (data file record) in the IMA SPREADSHEET data products
    has seven (7) 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 - SENSOR or MODE. The SENSOR rows are the
          IMA science data for each mass channel (32 channels).  The
          32 SENSOR rows are followed by 10 rows of MODE data for the
          same time period.  The MODE rows contain informational data
          such Mask indicators, Indexes, and Summations.
       4. Data Type Id - Numeric ID indicating SENSOR or MODE.
       5. Data Name - Short description for data on that row.  For
          example 'Mass Channel x' where x = 0-31 to indicate the
          mass channel in the SENSOR rows or 'Polar Angle Index' for
          informational data (MODE row).
       6. Data Unit - Indicates the data unit (c/acc for SENSOR
          data, unitless for MODE data).
       7. Values - These are the actual data values.  For this column
          there are multiple values as indicated by the ITEMS keyword
          in the label files.  For IMA data, there are 96 ITEMS.  In
          the SENSOR rows, these are the science data sampled for
          each energy step starting at 0 and ending at 95.  The MODE
          data rows contain only one value each with remaining ITEMS
          indicated as 'missing' with nothing between the commas
          (value,,...,,).  Please note that the data values are
          formatted for best accuracy and that this is not the
          accuracy of the IMA instrumentation.  In addition, even
          though the IMA data are in units of c/acc (raw counts)
          which are typically integer values, the data are formatted
          with 2-3 decimal places to account for possible fractions
          that can occur due to onboard data compression and ground
          data decompression.

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

    The Standard Data Products for IMA PSA Level 1b (EDR) products
    are:

       1. IMA_AZ00_C_ACC - Ion Mass Analyzer AZimuth anode 0 data
          in Counts / ACCumulation units.

       2. IMA_AZ01_C_ACC - Ion Mass Analyzer AZimuth anode 1 data
          in Counts / ACCumulation units.

       3. IMA_AZ02_C_ACC - Ion Mass Analyzer AZimuth anode 2 data
          in Counts / ACCumulation units.

       4. IMA_AZ03_C_ACC - Ion Mass Analyzer AZimuth anode 3 data
          in Counts / ACCumulation units.

       5. IMA_AZ04_C_ACC - Ion Mass Analyzer AZimuth anode 4 data
          in Counts / ACCumulation units.

       6. IMA_AZ05_C_ACC - Ion Mass Analyzer AZimuth anode 5 data
          in Counts / ACCumulation units.

       7. IMA_AZ06_C_ACC - Ion Mass Analyzer AZimuth anode 6 data
          in Counts / ACCumulation units.

       8. IMA_AZ07_C_ACC - Ion Mass Analyzer AZimuth anode 7 data
          in Counts / ACCumulation units.

       9. IMA_AZ08_C_ACC - Ion Mass Analyzer AZimuth anode 8 data
          in Counts / ACCumulation units.

      10. IMA_AZ09_C_ACC - Ion Mass Analyzer AZimuth anode 9 data
          in Counts / ACCumulation units.

      11. IMA_AZ10_C_ACC - Ion Mass Analyzer AZimuth anode 10 data
          in Counts / ACCumulation units.

      12. IMA_AZ11_C_ACC - Ion Mass Analyzer AZimuth anode 11 data
          in Counts / ACCumulation units.

      13. IMA_AZ12_C_ACC - Ion Mass Analyzer AZimuth anode 12 data
          in Counts / ACCumulation units.

      14. IMA_AZ13_C_ACC - Ion Mass Analyzer AZimuth anode 13 data
          in Counts / ACCumulation units.

      15. IMA_AZ14_C_ACC - Ion Mass Analyzer AZimuth anode 14 data
          in Counts / ACCumulation units.

      16. IMA_AZ15_C_ACC - Ion Mass Analyzer AZimuth anode 15 data
          in Counts / ACCumulation units.

    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 - MEX_ASPERA3_PSA_ICD_V02_00) found in the
    DOCUMENT directory 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:
    ======================

    IMA cannot measure the positive ions at very low energies and
    are indicated by negative values for the CENTER_ENERGY for the
    energy steps affected in the IMA_ENERGYn.TAB files in the CALIB
    directory.  Data at these energy levels should be ignored and
    not used.  Also included in the IMA_ENERGYn.TAB files are the
    elevation angles per polar angle index and per energy step.
    Elevation angles than -50.0 (degrees) indicate invalid data that
    should also be excluded from data analysis.

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

    The ASPERA-3 IMA data is complicated and there are many issues to
    address when analyzing the data. The IMA_CALIBRATION_REPORT.PDF
    (in the DOCUMENT directory) addresses many of these issues and it
    is strongly advised to contact the ASPERA-3 IMA team in guidance
    in analyzing the IMA data.

 ** Please contact the ASPERA-3 IMA Team for more information before
     using IMA data:
       Rickard Lundin - rickard@irf.se
       Stas Barabash - stas@irf.se
       Andrei Fedorov - Andrei.Fedorov@cesr.fr