Computer Science – Sound
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja.....9597p&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #9597
Computer Science
Sound
Scientific paper
According to the Mars Express mission , the MARSIS primary scientific objectives are to map the distribution of water, both liquid and solid, in the upper portions of the crust of Mars. Detection of such reservoirs of water will address key issues in the hydrologic, geologic, climatic and possible biologic evolution of Mars, including the current and past global inventory of water, mechanisms of transport and storage of water. Three secondary objectives are defined for the MARSIS experiment: subsurface geologic probing, surface characterization, and ionosphere sounding. According to the previous scientific objectives, this paper provides a description of the operational planning (in particular of the operative mode and frequency selection, taking into account of the MOLA data on the selected orbit) and expected performances of the MARSIS. The principle of operation of MARSIS is the following: the transmitted radar pulse will reach the top of the Mars surface producing a first reflection echo which propagates backward to the radar. However, due to the long wavelengths employed, a significant fraction of the e.m. energy impinging on the surface is transmitted into the crust and propagates downward. Additional reflections, due to subsurface dielectric discontinuities, will occur and the relevant echoes will propagate backward to the radar. As consequence time domain analysis of the strong surface return, eventually after multi-look non-coherent integration, will allow estimation of surface roughness, reflectivity and mean distance, just like in classical pulse limited surface radar altimeters. The presence of weaker signals after the first strong surface return will enable the detection of subsurface interfaces, while the estimation of their time delay from the first surface signal will allow the measurement of the depth of the detected interfaces. The detection of these subsurface echoes is limited by the surface echoes (especially if surfaces are rough), for this reason three different methods will be implemented in MARSIS: Doppler Beam Sharpening, Secondary Monopole Antenna, and Dual Frequency Processing. Finally, the MARSIS frequency-agile design will allow to tune the sounding parameters in response to changes in sun illumination condition.
Biccari Daniela
Cicchetti Andrea
Gurnett Donald A.
Johnson William T. K.
Jordan Rolando L.
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