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.