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.