Data Set Overview
  =================
    The Mars Express Mars Advanced Radar for Subsurface and Active
    Ionospheric Sounding (MARSIS) data set includes all spectral
    information calibrated in units of spectral density for the
    Active Ionospheric Sounder over the  Mars Express
    mission.  This data set includes calibrated values for each
    transmit event and the corresponding temporal data for each
    frequency channel.


  Parameters
  ==========
    This data set comprises the electric field spectral densities
    obtained via the electric dipole antenna sensor.


  Processing
  ==========
    Data in this data set were processed by the use of a number of
    software programs.  These programs re-assembled and
    de-compressed the raw telemetry data.  These raw values were
    then calibrated into physical units: power received by the
    electric antenna.  The data products were calibrated using the
    best calibration tables and algorithms available at the time
    of data archiving.  Should a significant improvement in
    calibration become available, an erratum will be noted in the
    erratum section.  Later versions of the products may contain
    better calibrations.

  Data
  ====
    The AIS calibrated full resolution data set includes several
    binary tables of wave spectra as a function of time from each of
    the various transmit events.  Each table will contain fixed-
    length records including columns for time, transmit frequency,
    and spectral densities from the temporal measurements.  The
    number of transmit frequencies is constant at 160 frequencies per
    frame and the number of samples per transmit frequency is
    constant at 80 per transmit pulse.

    Interpreting the provided intensities as remote emissions requires
    knowledge of the time delay between the emitted pulse and the
    measured electric spectral density.  The time offsets from the onset
    of the transmit pulse until the measurement of each spectral density
    value may be found from the relation:

       delay time (microseconds) = 167.443 + 91.4286 * (item-1)

    where item is the ITEM number from the SPECTRAL density column of
    the AIS_TABLE data products.  The first item value is 1, not 0.

    To make this more explicit these time values are pre-calculated
    in the table below.

         ITEM*  Delay (microsec)      ITEM*   Delay (microsec)
         ----   ----------------      ----    ----------------
            1             167.44        41             3824.59
            2             258.87        42             3916.02
            3             350.30        43             4007.44
            4             441.73        44             4098.87
            5             533.16        45             4190.30
            6             624.59        46             4281.73
            7             716.01        47             4373.16
            8             807.44        48             4464.59
            9             898.87        49             4556.02
           10             990.30        50             4647.44
           11            1081.73        51             4738.87
           12            1173.16        52             4830.30
           13            1264.59        53             4921.73
           14            1356.01        54             5013.16
           15            1447.44        55             5104.59
           16            1538.87        56             5196.02
           17            1630.30        57             5287.44
           18            1721.73        58             5378.87
           19            1813.16        59             5470.30
           20            1904.59        60             5561.73
           21            1996.02        61             5653.16
           22            2087.44        62             5744.59
           23            2178.87        63             5836.02
           24            2270.30        64             5927.44
           25            2361.73        65             6018.87
           26            2453.16        66             6110.30
           27            2544.59        67             6201.73
           28            2636.02        68             6293.16
           29            2727.44        69             6384.59
           30            2818.87        70             6476.02
           31            2910.30        71             6567.45
           32            3001.73        72             6658.87
           33            3093.16        73             6750.30
           34            3184.59        74             6841.73
           35            3276.02        75             6933.16
           36            3367.44        76             7024.59
           37            3458.87        77             7116.02
           38            3550.30        78             7207.45
           39            3641.73        79             7298.87
           40            3733.16        80             7390.30
         -----------------------      ------------------------
         * Here ITEM refers to the ITEM number of the column
           named SPECTRAL_DENSITY in the AIS_TABLE of the
           data products on this volume.

    A basic method for determining the range at which an emission was
    generated is to multiply the delays above with 1/2 the speed of
    light in a vacuum.

      apparent range (kilometers) =  0.1499 * (167.443 + 91.4286 * (item-1))

    The assumption that the signal propagates at the speed of light in
    a vacuum does not hold when the pulse traverses regions where the
    local plasma frequency is near the pulse frequency.  For more
    information on these effects and more see the file:

         AIS_SIGNAL_PROCESSING_REQ.PDF

    in the DOCUMENT directory of this volume.


  Ancillary Data
  ==============
    No Ancillary data are provided.


  Coordinate System
  =================
    The data in this data set are measurements of wave electric
    fields measured by the MARSIS electric sensors.  These fields are
    presented as detected by the sensors and are not rotated into any
    other coordinate system.  If desired the SPICE kernels can be
    used with the SPICE toolkit to convert from the spacecraft frame
    to virtually any frame which may be of use in analyzing these
    data.  However, for many purposes, the wave amplitudes are
    extremely useful and may be entirely adequate with no coordinate
    transformations at all.


  Software
  ========
    Sample code is provided with these data which demonstrates how
    to read these files in order to build a set of time-ordered
    wave spectra.  The sample code and algorithms are found in the
    SOFTWARE directory.


  Confidence Level Overview
  =========================
    This data set contains all active ionospheric calibrated data for
    the Mars Express MARSIS for the interval described above.  Every
    effort has been made to ensure that all data returned to Iowa
    from the spacecraft is included and that the calibration is
    accurate.


  Review
  ======
    The MARSIS active ionospheric sounder data will be reviewed
    internally by the Mars Express MARSIS team prior to release to
    the PDS. The data set will also be peer reviewed by the PDS.


  Data Coverage and Quality
  =========================
    All data in the stated interval are included to the best of our
    knowledge and attempts to determine completeness.  In general,
    the instrument was operated only briefly during early cruise
    phase for the purpose of Antenna deployment and periodic
    instrument health. During this time, flight restrictions
    precluded any transmit events and hence no science data.

    Beginning in June of 2005 commissioning of the instrument
    commenced more-or-less continuously for about a month.  During
    this period instrument gain settings and transmit frequencies
    were optimized for maximum signal-to-noise ratios as well as
    avoidance of interference generated by the spacecraft and by
    other instruments.


  Limitations
  ===========
    One measurement quality issue deals with the data compression
    algorithm used by the MARSIS onboard processor, which generates
    values of zero when the measured AIS values should be small but
    non-zero.

Corrupted data have been flagged in data
                             files where they occurred.  The label file
                             for each data product contains an entry
                             to flag this condition.