SHARAD

SHARAD
Name	SHAllow RADar (SHARAD)
Mission	Mars Reconnaissance Orbiter
Operator	Jet Propulsion Laboratory / California Institute of Technology
Launched	August 12, 2005
Launch vehicle	Atlas V
Launch site	Cape Canaveral Air Force Station
Orbit	Mars polar, mapping
Instrument type	subsurface sounding radar
Wavelength	15 MHz (center)
Heritage	derived from MARSIS heritage and European Space Agency techniques

SHARAD SHARAD is a high-frequency subsurface-sounding radar flown on the Mars Reconnaissance Orbiter that maps Mars' near-surface stratigraphy and dielectric properties. Developed by the Italian Space Agency in collaboration with the Jet Propulsion Laboratory and NASA, it complements radar sensors such as MARSIS and airborne instruments like Arecibo Observatory observations by providing higher vertical resolution over regional and local scales. The instrument has produced three-dimensional views of layered deposits, buried impact structures, and potential ice-rich units that inform studies linked to Viking program legacy datasets and modern exploration campaigns.

Overview

SHARAD operates as a nadir-looking synthetic-aperture radar payload on the Mars Reconnaissance Orbiter and targets frequencies chosen to balance resolution with penetration through Martian materials. It was proposed within the context of international cooperation involving the Italian Space Agency, Jet Propulsion Laboratory, NASA headquarters, and scientific teams connected to institutions such as Brown University, Cornell University, University of Arizona, and Caltech. The instrument's primary science objectives intersect with programs and missions including Mars Global Surveyor, Mars Odyssey, Spirit (rover), Opportunity (rover), and later projects like Mars Science Laboratory and Perseverance (rover), by providing subsurface context to landing-site geology, polar stratigraphy, and volatile reservoirs.

Design and Instrumentation

SHARAD's hardware architecture centers on a radar transmitter/receiver, deployable antenna, and on-board processors integrated with the Mars Reconnaissance Orbiter avionics and communications systems. The instrument transmits a 10–30 MHz chirped pulse and records echoes with a vertical resolution finer than that of the lower-frequency MARSIS instrument, enabling detailed discrimination of layers analogous to stratigraphic work from United States Geological Survey teams. The antenna is a 10-meter, dual-slot structure mechanically stowed at launch and deployed in Mars orbit by mechanisms designed with guidance from Lockheed Martin and tested at facilities like the Jet Propulsion Laboratory testbeds. Electronic components and calibration subsystems trace lineage to radar engineering advances at Thales Alenia Space and academic groups at Massachusetts Institute of Technology and Stanford University.

Mission Operations and Data Processing

Mission operations for the instrument coordinated Jet Propulsion Laboratory flight operations, science planning teams at institutions such as Brown University and Cornell University, and international partners including the Italian Space Agency and Agenzia Spaziale Italiana facilities. Data are acquired during targeted passes over polar and mid-latitude terrains, downlinked via the Deep Space Network to processing centers at Caltech and partner institutions. Raw echo data undergo range compression, motion compensation, synthetic aperture focusing, and clutter mitigation using processing chains developed by teams affiliated with University of Rome, University of California, Los Angeles, and Washington University in St. Louis. Processed radargrams are archived in planetary data systems used by agencies such as NASA and analyzed by investigators at centers including University of Colorado Boulder, Brown University, and University of Oxford.

Scientific Results

SHARAD has revealed subsurface stratigraphy in the Martian polar caps, detected buried impact craters under mantling deposits, and identified laterally extensive, radar-bright units interpreted as nearly pure water ice in mid-latitude lobate debris aprons and concentric crater fill. These findings cross-inform geomorphologic analyses from teams associated with US Geological Survey, Smithsonian Institution, and Max Planck Institute for Solar System Research. SHARAD data constrained deposits correlated with observations by the High Resolution Imaging Science Experiment and spectral datasets from Compact Reconnaissance Imaging Spectrometer for Mars and Thermal Emission Imaging System, yielding integrated interpretations of age, depositional processes, and volatile history relevant to hypotheses debated at conferences like the Lunar and Planetary Science Conference and publications in journals such as Science and Nature Geoscience. The instrument also mapped dielectric contrasts associated with layered terrains in regions tied to landing site assessments for Mars Science Laboratory and Mars 2020.

Calibration and Validation

Calibration efforts for the radar leveraged natural and engineered targets: polar layered deposits, known impact basins, and comparisons with active radar campaigns such as those at Arecibo Observatory and passive sounding from assets like Mars Express. Cross-validation included correlating radar horizons with surface exposures identified in images from HiRISE and morphological mapping from CTX (instrument), with teams from University of Arizona and Brown University quantifying permittivity and loss tangent estimates. Laboratory dielectric measurements at institutions such as NASA Ames Research Center and Jet Propulsion Laboratory supported inversion models used to estimate ice purity and porosity in subsurface units.

Limitations and Challenges

Limitations include depth-of-penetration tradeoffs inherent to SHARAD’s higher frequency relative to MARSIS, leading to shallower penetration in high-loss materials and susceptibility to clutter from surface roughness and steep topography noted over regions mapped by Mars Orbiter Laser Altimeter and Mars Orbiter Camera studies. IonosphERIC effects associated with Sun activity and diurnal electron content variations impacted signal coherence, requiring mitigation strategies developed with input from researchers at University of Colorado Boulder and Cornell University. Processing challenges include discriminating multiple scattering, resolving ambiguous dielectric layering in heterogeneous terrains, and integrating multi-instrument datasets from missions like Mars Reconnaissance Orbiter and Mars Global Surveyor to produce robust geophysical interpretations.

Category:Instruments aboard the Mars Reconnaissance Orbiter