Computer Science – Sound
Scientific paper
Jan 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998lpico.953q...3b&link_type=abstract
The First International Conference on Mars Polar Science and Exploration, Proceedings of the Conference held at Camp Allen, TX.
Computer Science
Sound
Echo Sounding, Geophysics, Ice, Mars Surface, Remote Sensing, Sounding, Mars (Planet), Antenna Design, Mars Missions, Piezoelectric Crystals, Radio Echoes, Roving Vehicles, Mars Exploration
Scientific paper
Of the many geophysical remote-sensing techniques available today, a few are suitable for the water ice-rich, layered material expected at the north martian ice cap. Radio echo sounding has been used for several decades to determine ice thickness and internal structure. Selection of operating frequency is a tradeoff between signal attenuation (which typically increases with frequency and ice temperature) and resolution (which is proportional to wavelength). Antenna configuration and size will be additional considerations for a mission to Mars. Several configurations for ice-penetrating radar systems are discussed: these include orbiter-borne sounders, sounding antennas trailed by balloons and penetrators, and lander-borne systems. Lander-borne systems could include short-wave systems capable of resolving fine structure and layering in the upper meters beneath the lander. Spread-spectrum and deconvolution techniques can be used to increase the depth capability of a radar system. If soundings over several locations are available (e.g., with balloons, rovers, or panning short-wave systems), then it will be easier to resolve internal layering, variations in basal reflection coefficient (from which material properties may be inferred), and the geometry of nonhorizontal features. Sonic sounding has a long history in oil and gas exploration. It is, however, unlikely that large explosive charges, or even swept-frequency techniques such as Vibroseis, would be suitable for a Polar lander -- these systems are capable of penetrating several kilometers of material at frequencies of 10-200 Hz, but the energy required to generate the sound waves is large and potentially destructive. The use of audio-frequency and ultrasonic sound generated by piezoelectric crystals is discussed as a possible method to explore layering and fine features in the upper meters of the ice cap. Appropriate choice of transducer(s) will permit operation over a range of fixed or modulated frequencies. Neutron scattering is used in soil science to assess the moisture content of soil. The technique relies on observing the effects of collisions between source neutrons and the H atoms in the material under test. Such a system maybe useful in assessing ice content-from within a borehole. Sounding of a several-kilometer-deep ice cap presents some considerable obstacles. There are, however, several methods that could be used to sound the upper meters of the ice cap in considerable detail.
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