Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p53a1502a&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P53A-1502
Physics
[6250] Planetary Sciences: Solar System Objects / Moon
Scientific paper
Lab experiments were conducted to analyze and study the attenuation phenomena of the electromagnetic waves which could be used to indicate the subsurface material on the moon. Intrinsic attenuation is defined as the amount of energy absorbed by the material. Although attenuation might not be able to uniquely identify the mineralogy, it could be a good indicator of the chemistry of the subsurface. With the total lack of liquid water at or near the surface of the moon, the changes in electric properties and attenuation are related only to changes in mineralogy. We observed the GPR signal amplitude at two different time steps as it traveled in a homogeneous material. The ratio of these two amplitudes provides a reliable measure of the attenuation factor in that material using the amplitude ratio formula. Given that the scattering and reflection coefficient are identical for both measurement, the amplitude ratio becomes a function of geometric spreading and intrinsic attenuation. A GPR signal propagating through high concentrations of ilmenite is expected to be of less energy relative to the signal which propagates through material having less ilmenite or iron bearing minerals. To practically test this hypothesis, preliminary GPR fieldwork has been conducted in Howard County, AR. where the main source for the heavy-mineral sands bearing ilmenite is found in the outcropping Tokio formation. The site was previously surveyed and a number of shallow drill holes were used to collected soil samples. The samples were used to determine the percentage of ilmenite and heavy minerals in the upper several meters of the earth surface. This data was used as ground truth data for the GPR surveys. We used GSSI, 400 MHz and 270 MHz antennas for data acquisition. Energy levels were compared in different GPR profiles in order to verify the relationship between the observed energy level and the ilmenite concentration. Due to the complexity in the scattering mechanism, amplitude representations of the profiles become impractical to compare. Average energy in the EM wave becomes more indicative of the intrinsic attenuation since it smoothes the high-frequency and sharp changes due to scattering. Our preliminary results show that energy profiles clearly indicate differences in the energy level between the high ilmenite and the low ilmenite regions.
Al-Shukri H. J.
Biris Alex
Mahdi Hanan
Su Meng
Trigwell Steven
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