1,720,986 research outputs found
“Dielectric Measurements of Saline Ices: Implications for Jovian Satellites Radar Exploration”.
No full textAutomated reflection strength tracking for improved stratigraphic interpretation of GPR data sets
No full textWe developed an algorithm to automatically detect and track reflections within GPR data sets, based on their reflection strength. The procedure divides each GPR trace into a series of energy packets, each containing reflected, diffracted, interfering, or noise-related signals. Close packets in nearby traces are then connected, using the local reflection dips, to create a web covering the entire GPR profile. Through this web, the algorithm tracks, and marks as horizons, the main reflections, while redundant horizons and possible false positives are automatically removed. The procedure can be applied with just minimal signal processing, and requires only limited input from the interpreter. The algorithm was able to accurately track all the recorded reflections within GPR data sets acquired on coastal sand dunes, and to filter out deeper false positives
Automated detection and tracking of hyperbolic diffractions applied to engineering GPR data sets
No full textWe developed an algorithm to automatically detect and track hyperbolic diffractions within GPR data sets. The procedure uses the apexes as initial seeds, and also pre-estimates the widths of their hyperbolas, thus producing a more objective search window that is automatically adapted to local conditions. Within the search window, hyperbolas with varying EM velocities are fitted to the signal phases surrounding the initial seed, which are then connected to form preliminary hyperbolic paths. Among these paths, the algorithm selects the best fit by assessing several attributes, while possible false positives and redundant hyperbolas are subsequently removed. The proposed procedure can be applied with minimal signal processing, and it requires only limited input from the interpreter. The algorithm was able to accurately track most diffractions within engineering GPR data sets, with very few false positives and negatives
Dielectric measurements and radar attenuation estimation of ice/basalt sand mixtures as martian Polar Caps analogues
No full textThe nature of the materials underlying the superficial deposits of Mars can be inferred, applying an inversion
algorithm, from the data acquired by the orbiting HF radars MARSIS and SHARAD. This approach
requires the knowledge of the electromagnetic properties of the shallow deposits and an accurate evaluation
of the signal attenuation. The present work is focused on the determination of the dielectric
parameters of several geo-materials. We performed the measurements of the complex permittivity, in
a wide range of temperature (150–250 K) and frequency (20 Hz–1 MHz), on pure water ice, dry basalt
sand and ice/basalt mixtures with different sand volume fractions. The data are presented in terms of
attenuation as a function of basalt volume fraction, frequency and temperature, and discussed in terms
of extrapolation to MARSIS and SHARAD frequency bands. The results show that, besides the expected
dependence of the attenuation from temperature, the presence of the solid inclusions in the ice strongly
affects the behaviour of the attenuation versus frequency
Dielectric characterization of ice/MgSO4.11H2O mixtures as Jovian icy moon crust analogues
No full textOne of the main objectives of proposed missions to the icy Jovian moons is to prove the existence of the postulated subsurface ocean on Europa using radar sounders. The success of these missions will rely on the ability of the radar signals to penetrate ten kilometers of icy material that could potentially contain various types of impurities. In this work we quantify the impact of magnesium sulfate hydrates on the electrical properties of water ice by performing a series of dielectric measurements on different ice/MgSO4.11H2O mixtures as a function of frequency and at temperatures comparable with those expected on the icy satellite surfaces. Our results indicate that the salt only affects the real part of permittivity of the mixtures, whereas the imaginary part, hence the attenuation, does not significantly differ from that of pure ice. This means that in some regions signal penetration may be better than previously thought
Electromagnetic characterization of saline/acid ice mixture for shallow radar exploration
No full textThe aim of this work is the estimation of the electromagnetic parameters of the icy geomaterials present in Jovian satellite crusts. The first recognition of the Jupiter system, performed by the Voyager spacecraft, suggested the possibility of an ocean of liquid water beneath the ice shell of the two Jupiter's moons, Ganymede and Europa. In addition, the Galileo mission detected in the icy shell the presence of impurities like magnesium and sodium sulfates, and sulfuric and chloridric acids. JUICE - JUpiter ICy moons Explorer will investigate the potentially habitable zones in the Ganymede, Europa and Callisto moons. In particular a radar sounder (RIME) operating at 9 MHz, optimized for the penetration of the icy shell, will provide the subsurface survey up to a depth of about 9 km. The performance of RIME depends on the electromagnetic properties of the icy shells, which in turn are related to the impurity contents and temperature. In this scenario, we have performed measurements of dielectric properties of ice doped with MgSO4 , Na2SO4 , H2SO4 and HCl. The tests were performed as a function of frequency from 20 Hz to 30 MHz and temperature down to 100 K. In particular, the dielectric properties of the ice samples were measured using a capacitive cell and LCR meters. The values of real and imaginary parts of dielectric permittivity allow us to estimate velocity and attenuation of radar signals versus salts and acids content, to optimize the JUICE mission data analysis
Coaxial-Cage Line for Geo-materials Electromagnetic Characterization
No full textWe present the results obtained with a
custom coaxial-cage line built to measure the
complex dielectric permittivity and magnetic
permeability of granular and/or liquid materials.
The coaxial-cage line presents an open structure to
facilitate the insertion and to control the
compactness
of
granular
materials.
The
measurements have been performed using a Vector
Network Analyzer and the electromagnetic
parameters of the samples have been retrieved
through the Nicolson-Ross-Weir algorithm (in case
of magnetic materials) or the Boughriet algorithm
(in case of non-magnetic ones). The cell has been
used to characterize the electromagnetic properties
of some geo-materials (clay soils and magnetite
samples). The electromagnetic parameters are
shown as a function of frequency (1MHz-1GHz) and
temperature (about 200-298K)
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