Data Set Overview
    =================

    This archive contains radargram image data acquired by the Mars
    Reconnaissance Orbiter (MRO) Shallow Radar (SHARAD) instrument,
    which uses a 15-25 MHz radio signal to probe up to several
    kilometers through low-loss materials like the polar layered
    deposits, and up to a few hundred meters in typical geologic
    materials. Reflections occur where there are significant changes
    in the dielectric permittivity among layered deposits, occurring
    over lateral scales of at least a few kilometers. Radargrams are
    produced using a consistent set of synthetic aperture radar
    processing parameters described in the accompanying User's Guide.
    For each SHARAD track, the *RGRAM.IMG file is a real-valued image
    of the radar backscatter power, arranged with time delay on the
    vertical axis and along-track samples on the horizontal axis.
    These values are in arbitrary units of power. The along-track
    samples of each radargram are associated with latitude, longitude
    pairs in the ancillary *GEOM.TAB file, which also provides
    information on spacecraft position and planetary radius for use in
    changing the reference spheroid surface. Along-track spacing of
    the radargram samples is 128 pixels per degree, or about 460 m.
    The round-trip delay samples are a uniform 0.0375 microseconds.
    Browse products are presented in a logarithmic (decibel) format
    with a greyscale range corresponding to 35 dB.

    This archive includes data processed by the U.S. SHARAD team.
    Differences in the processing methods and resulting radargrams
    from the PDS archive products delivered by the SHARAD Italian
    science team are noted in the accompanying User's Guide (DOCUMENT
    directory). The Italian products are available as a separate PDS
    archive: http://pds-geosciences.wustl.edu/missions/mro/sharad.htm.


    Processing
    ==========

    SHARAD transmits a linear frequency-modulated chirp signal with a
    bandwidth of 10 MHz (15-25 MHz frequency). Data processing is
    described in detail in the accompanying User's Guide (see the
    DOCUMENT directory). In brief, the received signals are
    range-compressed by convolution with a model for the transmitted
    waveform, then processed using synthetic aperture radar techniques
    to improve the signal-to-noise performance and narrow the
    along-track resolution to a few hundred meters. Cross-track
    resolution is limited only by the delay window and the roughness
    of the surface, so significant 'clutter' can appear within the
    radargram from surface features some distance to either side of
    the nadir track. An empirical model for ionospheric delay effects
    is applied to bring the vertical registration among crossing
    tracks into better agreement.

    Data
    ====

    The 32-bit values in the *RGRAM.IMG files correspond to arbitrary
    units of received signal power. Since the instrument is relatively
    stable over time, and all synthetic aperture processing parameters
    are held constant across the archive, it is possible to compare
    these power values along and among SHARAD tracks. It must be
    noted, however, that significant variations in the signal level
    are associated with the roll angle of the spacecraft, and minor
    variations occur due to the positions of the spacecraft high-gain
    antenna and solar panels. Ionospheric attenuation also occurs
    during daytime SHARAD observations; while this has been
    characterized, no correction is applied to the archive products.
    The vertical delay resolution is presented at a spacing of 0.0375
    microseconds, which is approximately a factor of two oversampled
    with respect to the resolution dictated by the 10-MHz bandwidth of
    the transmitted chirp signal.


    Coordinate System
    =================

    The coordinate system is planetocentric, with longitude positive
    toward the east. The SHARAD radargrams are presented in a two
    dimensional format, with round-trip time delay along the vertical
    axis and along-track distance on the horizontal axis. The vertical
    scale is a uniform 0.0375 microseconds in round-trip delay. The
    center range cell of each image column is adjusted to match the
    round-trip time delay to the location of the MOLA areoid, and the
    GEOM.TAB file for each image contains the required information to
    shift to a different reference planetary shape. The horizontal
    samples are posted at 128 pixels per degree, corresponding to
    approximately 460 m horizontal distance along the ground track.
    The *GEOM.TAB file also contains a latitude and longitude location
    for each radargram column.

    Please see RGRAM_PROCESSING.PDF in the DOCUMENT directory for more
    information.

Confidence Level Overview
    =========================
      TBD


    Review
    ======
      This data set was examined by a peer review panel in accordance
      with PDS procedures.


    Data Coverage and Quality
    =========================
      See RGRAM_PROCESSING.PDF in the DOCUMENT directory.

    Limitations
    ===========
      See RGRAM_PROCESSING.PDF in the DOCUMENT directory.