A. De Santis

Electromagnetic propagation features of ground penetrating radars for the exploration of martian subsurface

In this work, the effects of magnetic inclusions in a Mars-like soil are considered with reference to the electromagnetic propagation features of ground-penetrating radars (GPRs). Low-frequency and time-domain techniques, using L-C-R meters and TDR instruments, respectively, are implemented in laboratory experimental set-ups in order to evaluate complex permittivity and permeability and wave velocity for different scenarios of a dielectric background medium (silica) with magnetic inclusions (magnetite). Attenuation and maximum detection ranges have also been evaluated by taking into account a realistic GPR environment, which includes the transmitting/receiving antenna performance and the complex structure of the subsurface. The analysis and the interpretation of these results shed new light on the significant influence of magnetic inclusions on the performance of Martian orbiting and rover-driven GPRs.

Design and construction of a large test site to characterize the GPR response in the vadose zone

In this work Ground Penetrating Radar (GPR) and Time Domain Reflectometry (TDR) measurements are carried out on a test-site. The test site consists of a pit filled with gravel and sand in which a pipe system for water inflow is buried. The data are collected under different water charge conditions and the water level is monitored by piezometers. TDR measurements are performed at various depths using a multilevel probe system. GPR measurements are performed by using the single-offset reflection method with a system equipped with 250 MHz and 500 MHz antennas. The results pertaining to the water table depth estimations, obtained by calibrating time GPR section with TDR velocity data, have shown a good agreement with the piezometric responses.

Electromagnetic Parameters of Dielectric and Magnetic Mixtures Evaluated by Time-Domain Reflectometry

The frequency-domain analysis of time-domain reflectometry (TDR) data can be used to evaluate the electromagnetic (EM) parameters of a sample under test. The goal of this letter was to use TDR to determine EM parameters, assumed to be frequency independent, for various magnetite/glass-beads mixtures. The EM parameters are, in turn, used to determine the velocity and attenuation of propagating waves. The latter quantity is also obtained through the TDR voltage method. Velocities decrease, and attenuations increase with increasing magnetite content. The measurements of the present work are compared with the velocities and attenuations reported in the literature (measured via the network analyzer (NA) and LCR meter techniques). The velocities calculated using the various methods are in good agreement. In contrast, the attenuations determined by fitting the TDR data only agree with the NA measurements at high frequencies (450 MHz), while those obtained by the TDR voltage method match the low-frequency attenuations determined through the LCR meter. The reasons for these behaviors are discussed, and the need for precise handling of the TDR data is emphasized. The TDR fit procedure is recommended to obtain reliable EM parameters of materials.

Effective frequency and attenuation measurements of glass beads/magnetite mixtures by time-domain reflectometry

Samples with different percentages (5–30%) of magnetite and different ranges of grain size are analysed by time-domain reflectometry (TDR). The passband, the attenuation factor α and the effective frequency are derived from the TDR measurements. The passband was obtained from the second edge of the sample by eliminating the DC component and applying a Fourier transform to the residual signal. The bandwidth of the resulting spectral shape decreases as the magnetite percentage increases. The second edge was also used to evaluate the effective attenuation factor α e , using multiple-reflection theory, terminated at the second reflection. The attenuation values α can be estimated independently by means of the electromagnetic parameters obtained using an LCR meter. To compare α and α e , an effective TDR frequency ν e is introduced. The agreement between the values obtained from TDR and LCR-meter techniques supports the reliability of the attenuation derived from the second TDR reflection, and that computed from the effective frequency. The shapes of the passbands and the α e and ν e values for magnetite/glass-beads mixtures, which simulate dry soils with increasing iron oxides content, are reported and discussed.

On the attenuation factor measurements of glass beads/magnetite mixtures and on the effective frequency evaluation by time domain reflectometry

AhtracrSamples with different percentages (5-25%) of magnetite and different grains size ranges are analyzed by Time Domain Reflectometry (TDR) for deriving the bandwidth and the attenuation factor a . The spectral content of the signal changes as function of the material investigated. Indeed, the bandwidths narrow with the increasing of magnetite volume content of the sample. The spectral information coming from the bandwidth and the attenuations values were used to evaluate the effective frequency of the TDR signal. The attenuation factor values are obtained by. two different methods: i) wave amplitude at the second reflection, ii) electromagnetic parameters (evaluated with L-C-R meters) and TDR band widths. The two methods provide consistent a values within the experimental uncertainties. The agreement supports the possibility of measuring the attenuation factor from the second TDR reflection.

Effect of Electromagnetic Soil Parameters on Early-Time GPR Signals

In the present work, a comparison between Time Domain Reflectometry (TDR) and Ground Penetrating Radar (GPR) measurement on a test site is performed. The finale scope of the experimental study was to explore the possibility to develop a new approach to water content estimation, based on the analysis of the GPR early-time response. Instantaneous amplitude signal of the first 8 ns have been compared with electrical parameters (and dc) extracted from TDR measurements. The tests were conducted in a specifically designed site, in which the soil water content could be varied. The results show a good correlation between the GPR instantaneous amplitude data and soil electromagnetic properties.