Mathematics – Logic
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p34a..06r&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P34A-06
Mathematics
Logic
[5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering, [5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties, [5494] Planetary Sciences: Solid Surface Planets / Instruments And Techniques, [6250] Planetary Sciences: Solar System Objects / Moon
Scientific paper
Ground-Penetrating Radar (GPR) data from terrestrial analog environments can help constrain models for evolution of the lunar surface, aid in interpretation of orbital SAR data, and help predict what might be encountered in the subsurface during future, landed, scientific or engineering operations on the Moon. GPR can yield insight into the physical properties, clast-size distribution, and layering of the subsurface, granting a unique view of the processes affecting an area over geologic time. The purpose of our work is to demonstrate these capabilities at sites at which geologic processes, settings, and/or materials are similar to those that may be encountered on the moon, especially lava flows, impact-crater ejecta, and layered materials with varying properties. We present results from transects obtained at Barringer Meteor Crater, SP Volcano cinder cone, and Sunset Crater Volcano National Monument, all in northern Arizona. Transects were taken at several sites on the ejecta of Meteor Crater, all within a crater radius (~400 m) of the crater rim. Those taken across ejecta lobes or mounds reveal the subsurface contact of the ejecta upper surface and overlying, embaying sediments deposited by later alluvial, colluvial, and/or aeolian processes. Existing mine shafts and pits on the south side of the crater provide cross sections of the subsurface against which we compare adjacent GPR transects. The ‘actual’ number, size, and depth of clasts in the top 1-2 m of the subsurface are estimated from photos of the exposed cross sections. In GPR radargrams, reflections attributed to blocks in the top 2-5 m of the subsurface are counted, and their depth distribution noted. Taking GPR measurements along a transect at two frequencies (200 and 400 MHz) and to various depths, we obtain the ratio of the actual number of blocks in the subsurface to the number detectable with GPR, as well as an assessment of how GPR detections in ejecta decline with depth and depend on antenna frequency. This work allows calibration of GPR-based interpretations of ejecta processes. Work at SP volcano focuses on the northern, lower slopes of the cinder cone, from beneath which a basalt lava flow extends onto surrounding terrain. Layering within cinders is visible in GPR radargrams in the upper ~0.5 m. A small pit reveals that such layering may be due to significant, stratified variation in cinder size, relative moisture content of a fine, loess-like matrix, and fraction of inter-cinder voids, or pore space, filled with matrix. The subsurface cinder-lava contact, as well as some variation within the lava flow (possibly due to varying degrees of coherence and fracturing), is detected by the GPR. Our work will help frame tractable scientific questions in lunar mission development, and aid in interpretation of future returned data. A non-invasive alternative and complement to digging and drilling, GPR is also potentially useful in exploration of other terrestrial bodies.
Bussey Ben
Grant Alex J.
Russell Patrick S.
Williams Karina
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