Computer Science – Sound
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p33a1743f&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P33A-1743
Computer Science
Sound
[6055] Planetary Sciences: Comets And Small Bodies / Surfaces, [6094] Planetary Sciences: Comets And Small Bodies / Instruments And Techniques, [6210] Planetary Sciences: Solar System Objects / Comets, [7299] Seismology / General Or Miscellaneous
Scientific paper
The Mission Rosetta was launched to comet 67P/Churyumov-Gerasimenko in 2004. It will finally reach the comet and will deliver the Lander Philae at the surface of the nucleus in November 2014. The Lander carries ten experiments, one of which is the Surface Electric Sounding and Acoustic Monitoring Experiment (SESAME). Part of this experiment is the Comet Acoustic Surface Sounding Experiment (CASSE) housed in the three feet of the lander. The primary goal of CASSE is to determine the elastic parameters of the surface material, like the Young's modulus and the Poisson ratio. Additional goals are the determination of shallow structure, quantification of porosity, and the location of activity spots and thermally and impact caused cometary activity. We conduct calibration measurements with accelerometers identical to the flight model. The goal of these measurements is to develop inversion procedures for travel times and to estimate the expected accuracy that CASSE can achieve in terms of elastic wave velocity, elastic parameters, and source location. The experiments are conducted mainly on sandy soil, in dry, wet or frozen conditions, and apart from buildings with their reflecting walls and artificial noise sources. We expect that natural sources, like thermal cracking at sunrise and sunset, can be located to an accuracy of about 10 degrees in direction and a few decimeters (1σ) in distance if occurring within the sensor triangle and from first arrivals alone. The accuracy of the direction is essentially independent of the distance, whereas distance determination depends critically on the identification of later arrivals. Determination of elastic wave velocities on the comet will be conducted with controlled sources at known positions and are likely to achieve an accuracy of σ=15% for the velocity of the first arriving wave. Limitations are due to the fixed source-receiver geometry and the wavelength emitted by the CASSE piezo-ceramic sources. In addition to the deterministic evaluation of travel times we prepare a statistical interpretation of the medium in terms of scattering properties and seismogram coda. An existing 2D finite integration code able to handle not only velocity variations but also voids will be extended to 3D media in order to simulate porous cometary ices.
Faber Carel
Fischer Hanspeter
Hoppe Jens
Knapmeyer Martin
Seidensticker Klaus J.
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