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NASA Space Science Data Coordinated Archive Header



Availability: Data Identified but not Received

Time span: 2006-09-30 to 2006-11-28


This description was generated automatically using input from the Planetary Data System.

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:


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.


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.

These data are available on-line from the Planetary Data System (PDS) at:

Alternate Names



  • Planetary Science: Geology and Geophysics

Additional Information



Questions and comments about this data collection can be directed to: Dr. David R. Williams



NameRoleOriginal AffiliationE-mail
Dr. Roberto SeuData ProviderUniversita degli Studi di
Dr. Nathaniel E. PutzigGeneral ContactSouthwest Research
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