Data Set Overview
  =================
    Level 1b data are further processed to produce Level 2 data,
    i.e. data which have been calibrated, range-compressed and corrected
    for ionosphere distortion. Auxiliary information for Level 2 data
    is not modified, and thus the volume of auxiliary data accompanying
    Level 2 data is the same as for Level 1b data. Scientific data,
    however, are converted from 1-byte integer counts
    from the analogue-to-digital converter of the instrument
    to 4-byte real voltages, producing an increase of science data
    volume by a factor of four.
 
 
  Parameters
  ==========
    MARSIS data are organized into groups of echoes called frames. A frame
    contains one or more echoes, with or without on-board processing. Each
    echo, depending on the kind of processing it underwent, is recorded either
    as a time series of signal samples, or as the complex spectrum of the
    signal itself produced by means of a FFT. Scientific data in a frame are
    complemented by a set of ancillary data, produced by the instrument and
    recording parameter values used in pulse transmission,
    echo reception and on-board processing.
 
 
  Processing
  ==========
    The primary task of Level 2 data processor  is the
    Range Compression of the Marsis collected echoes during
    the subsurface modes (except for the SS2 Mode) and transmitted
    to the ground. These data are only compressed in azimuth on board
    (Doppler Filters output).
    Since these data have been distorted by the Ionosphere,
    we cannot use an ideal reference function (the ideal chirp)
    for range compression.
    Therefore we shall use the Contrast Method and/or
    the Front Surface Reflection (FSR) Method to estimate
    the Ionospheric distortion and to calculate a complex
    correction to modify the Ideal Reference Function in order
    to optimize the compressed signal.
    Note that the data related to the SS2 Mode will not be processed
    by the Level 2 processor, because they will be transmitted
    to the ground already compressed in time and also after
    a multi looking procedure.
 
    The Level 2 processor could elaborate the same data more times,
    using the information elaborated during
    the mission on the ionosphere and the instrument.
    This will signify a progressive improvement
    of the Level 2 data product.
    The Level 2 processing can be resumed in these steps :
 
     -| Data Decompression
     -| Ionospheric Dispersion Correction
         (Contrast Method and/or FSR Method)
     -| Range Compression
 
 
    Level 2 data distribution to the Co-Is and to the Mars Express
    mission archive is performed by ASDC. It is required by ESA that data
    products are delivered in batches of six-months worth
    of data within six months from the last data take
    (i.e. one year after the beginning of that particular data collection
    period), but it is necessary that level 1b processing be completed
    in a much shorter period, to allow enough time for level 2 data
    processing and data analysis within the MARSIS team before
    the expiration of the data proprietary period (which is the same
    six-month time span).
 
 
  Data
  ====
    The MARS EXPRESS MARS MARSIS REDUCED DATA RECORD SUBSURFACE V1.0
    Data Set contains subsurface-sounding data from the MARS EXPRESS MARS
    MARSIS EXPERIMENT DATA RECORD V1.0 Data Set that have been
    uncompressed, calibrated and, except for data acquired using
    the SS2 mode, range-processed after correcting for the distortion
    of the transmitted signal caused by the ionosphere.
    Geometric information needed to locate observations in space and
    time is also provided in the Data Set.
 
    The list of RDR data Products is :
 
    SSx_TRK_CMP_RDR : On-board processed Subsurface Sounding data
 
    Where   x   stands for a number between 1 and 5
 
    RDR Data Products are made by two files, each of which contains a PDS
    binary TABLE object preceded by a PDS attached label describing its
    structure. The first file, called Frame file (FRM) contains
    the instrument data proper, organised into individual frames.
    Each frame corresponds to a record in the file, which is also
    a row in the PDS binary TABLE object into which frames are organised.
    A Data Product contains all frames acquired using the same instrument
    mode in tracking (TRK) state during a single orbit.
    .
    The second file constituting an RDR Data Product is called a Geometry
    file (GEO), and contains one record, corresponding to one line
    of the PDS binary TABLE object into which data are organised,
    for every frame in the corresponding FRM file. Columns of the table
    contain the values of parameters describing the geometry
    of observation for the corresponding frame.
 
 
 
  Ancillary Data
  ==============
    Each frame of MARSIS data (with the exception of frames
    stored in flash memory) carries a 228 byte header of ancillary data,
    containing necessary information for subsequent analysis
    of the data and further processing.
    The exact content of the ancillary data depends on instrument mode.
 
 
 
  Coordinate System
  =================
    Locations on the surface of Mars are expressed in planetocentric
    coordinates. Longitude is comprised in the range 0 - 360 degrees.
 
 
  Software
  ========
    Marsis data products can be read by the PDS software NASAView, which
    reads a PDS label and displays the associated image or table.
    NASAView has been tested on both EDR and RDR data products.
 
 
  Media/Format
  ============
    The standard distribution format for the data is transfer through
    Internet from the Planetary Science Archive of ESA, which can be
    accessed at the following URL:
 
    http://www.rssd.esa.int/psa

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 journals. The dataset is
    currently being reviewed by the Plannetary Science Archive of ESA.
 
 
  Data Coverage and Quality
  =========================
    Data in this dataset have been acquired only in the last six months of
    the nominal mission, because of the delay in the deployment of the
    MARSIS antenna. Because of this, coverage is limited mainly to
    southern latitudes.
 
    Data quality in a data product label is indicated through the
    DATA_QUALITY_ID element, and measures the integrity of the telemetry
    stream from the instrument. The permitted values of DATA_QUALITY_ID
    are the following:
 
    -1: percentage of corrupted data not available
     0: no corrupted data
     1: less than 2% corrupted data
     2: less than 5% corrupted data
     3: less than 10% corrupted data
     4: more than 10% corrupted data
 
 
  Limitations
  ===========
    There are no known limitations at this time.