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Read Full Article (file size: 4599424 bytes) Cited by
JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 111,
E06S02,
doi:10.1029/2005JE002619,
2006
Absorption and scattering in ground-penetrating radar: Analysis of the Bishop Tuff
Robert E. Grimm
Department of Space Studies, Southwest Research Institute, Boulder, Colorado, USA
Essam Heggy
Lunar and Planetary Institute, Houston, Texas, USA
Stephen Clifford
Lunar and Planetary Institute, Houston, Texas, USA
Cynthia Dinwiddie
Department of Earth, Material, and Planetary Sciences, Southwest Research Institute, San Antonio, Texas, USA
Ronald McGinnis
Department of Earth, Material, and Planetary Sciences, Southwest Research Institute, San Antonio, Texas, USA
David Farrell
Center for Nuclear Waste Regulatory Analyses, Southwest Research Institute, San Antonio, Texas, USA
Abstract
Ground-penetrating radar (GPR) signals are attenuated by both absorption and scattering. We performed low-frequency (<100
MHz) GPR surveys at the Volcanic Tableland of the Bishop (California) Tuff to evaluate the factors that control GPR depth
of investigation and to develop insight into the capabilities of such radars for Mars. The subsurface reflection character
was very different for two different commercial systems used; together, they revealed both internal welding contacts in the
tuff and an abundance of discrete scatterers. Attenuation coefficients were computed from profiles that showed distributed
scattering: the semilogarithmic signal decay is directly analogous to seismic coda. The absorption (intrinsic loss) was determined
to be ∼1 dB/m from low-frequency vertical-electric soundings. The residual attenuation (that is, the attenuation in the absence
of absorption) is attributed to scattering. Scattering attenuation of ∼1 dB/m at 25–50 MHz corresponds to mean-free paths
as short as 4 m, a fraction of the two-way propagation distances of 20–40 m. Therefore the Bishop Tuff is formally a strong
scatterer to GPR. The mean-free path is also comparable to the subsurface radar wavelength in this case, maximizing scattering
loss. The scatterers themselves likely originate as welding heterogeneities; contrasts in dielectric constant due to density
differences may be supplemented by moisture variations. On Mars, scattering is likely to contribute significant losses to
GPR signals in all but the most uniform materials, and unfrozen thin films of water in the lower cryosphere could influence
both absorption and scattering.
Received 21
October
2005;
accepted 26
April
2006;
published 30
June
2006.
Keywords: ground-penetrating radar;
attenuation;
absorption;
scattering;
Mars.
Index Terms: 0994 Exploration Geophysics: Instruments and techniques; 5109 Physical Properties of Rocks: Magnetic and electrical properties (0925); 5144 Physical Properties of Rocks: Wave attenuation; 8404 Volcanology: Volcanoclastic deposits; 6225 Planetary Sciences: Solar System Objects: Mars.
Read Full Article (file size: 4599424 bytes) Cited by
Citation: Grimm, R. E., E. Heggy, S. Clifford, C. Dinwiddie, R. McGinnis, and D. Farrell
(2006),
Absorption and scattering in ground-penetrating radar: Analysis of the Bishop Tuff,
J. Geophys. Res.,
111,
E06S02,
doi:10.1029/2005JE002619.
Copyright 2006 by the American Geophysical Union.
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