Physics – Geophysics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p11e1625c&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P11E-1625
Physics
Geophysics
[0933] Exploration Geophysics / Remote Sensing, [0994] Exploration Geophysics / Instruments And Techniques, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
The MARSIS and SHARAD orbital radar sounders have given tantalizing glimpses of subsurface fof Mars. But, to be accommodated aboard spacecraft with a number of other high-level investigations, MARSIS and SHARAD had to accept some compromises in instrument design and operation that have limited their potential capabilities. Here we describe a proposal for a new Mars orbital radar mission, the Mars Global Subsurface Sounder (MGSS), that is solely dedicated to sub-surface sounding, allowing it to achieve maximum spatial resolution and penetration depth through an optimized orbit, antenna design, increased power and significantly improved signal to noise ratio. The chief science goals of this mission are to investigate the stratigraphic and structural evolution of the Martian subsurface and polar layered deposits (PLD), as well as the distribution and state of subsurface water (whether as a liquid or as massive ice deposits) through the acquisition of a 3-D radar map to depths ranging from 1 km, in lithic environments, and up to 4 km in the PLD. The MARSIS and SHARAD radar investigations have provided clear demonstrations of the capabilities of deep-sounding radar to conduct similar investigations. The MGSS is expected to significantly improve on this performance by taking advantage a spacecraft and mission optimized for radar sounding. Over its 2-year mission duration, the MGSS will be able to compile a global 3-D map of local variations in dielectric properties, with a horizontal resolution of ~1 km and vertical resolution of ~10-20 m MGSS is a dual-band radar sounder that operates at 1-6 MHz and 15-25 MHz. 2-D SAR processing is used to maximize both along and cross track resolution and clutter suppression, while onboard along track processing minimizes the downlink data rate. The spacecraft has sufficient mass margin to incorporate sufficient shielding minimize signal degradation by electromagnetic interference and maximize the signal to noise ratio. The orbit of MGSS is similar to that of NASA's MRO, being nearly sun synchronous at 92.6° at an altitude 300 km. This orbit results in the acquisition of 13 complete ground tracks across the planet each solar day, with an orbital precession rate of about 500 m/day. Thus, a full global survey can be completed in two Martian years. A synthetic aperture and cross-track array processing minimize the effects of surface clutter and improve the effective depth of sounding. The large synthetic aperture in cross track is formed by sequential orbital passes. The orbits are sufficiently random to eliminate grating lobes. Array processing techniques, such as constrained optimization, can then be used to steer nulls in the direction of the surface clutter. Significant improvements can be made in an orbital radar sounder's performance and coverage when the spacecraft and mission are optimized for this purpose. Examples of a terrestrial radar sounding investigation, employing similar techniques, can be found at:
Clifford Stephen M.
Delemere W.
Gogineni Prasad S.
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