ABSTRACT 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.
For a vector field defined by a scalar potential outside a surface enclosing all the sources, it is well known that the potential is defined uniquely if either the potential itself, or its derivative normal to the surface, is known everywhere on the surface. For a spherical surface, the normal derivative is the radial component of the field: the horizontal (vector) component of the field also gives uniqueness (except for any monopole contribution). This paper discusses the way other partial information of the field on the spherical surface can give a unique, or almost unique, knowledge of the external potential/field, bringing together and correcting previous work. For convenience the results are given in the context of the geomagnetic field B. This is often expressed in terms of its local Cartesian components (X, Y, Z), equivalent to (-Bø, Bθ,-Br); it can also be expressed in terms of Z and the vector horizontal component H = (X, Y). Alternatively, local ‘spherical polar’ components (F, I, D) are used, where F = ǀBǀ, the inclination I is the angle in the vertical plane downward from H to B, and the declination D is the angle in the horizontal plane eastward from north to H. Knowledge of X over the sphere gives a complete knowledge of the potential, apart from that of any monopole (which is zero in geomagnetism), and Y gives the potential except for any axially symmetric part (which can be provided by a knowledge of X along a meridian, or of H along any path from pole to pole). In terms of (F, I, D) the situation is more complicated; either For the total angle (I, D) needs to be known throughout a finite volume; for the latter, this paper shows how, in principle, the actual potential can be determined (except for an unknown scaling factor). Similarly D on the sphere also needs a knowledge of ǀHǀ on a line from (magnetic) pole to pole. We also discuss how these various properties affect the determination, by surface integration, of the Gauss coefficients of the field representation in terms of spherical harmonics.
Nine representative sherds from the old (14th–16th century) kilns at the Castle of Cafaggiolo in Tuscany have been analysed by means of internal microstratigraphic analyses and micro‐Raman spectroscopy and classified as follows: six engobed and glazed fragments, of which three are covered with an opaque white, decorated layer, one is marbleized, and two are engobed. The surface of the two engobed sherds, fragments of unfinished products, indicates that at least two firing processes were used. Two samples show characteristics of Byzantine pottery, and three of them can be classified as Islamic ware or maiolica , whilst the other one displays intermediate characteristics. The variety of ceramic wares indicates the presence of craftsmen with differing expertise, and suggests that part of their work was dedicated to experimentation on new ceramic production techniques.
The effects of centrifugal distortions on polarizability anisotropies are taken into account to explain the experimental Rayleigh spectrum of H2S. Centrifugal corrections are calculated following a first-order perturbation theory due to Toyama et al. The simulated spectrum agrees with the experimental one qualitatively, but the calculated corrections to the rotational transitions are not large enough to reproduce the experimental findings. Possible origins of that discrepancy and consequences of a significant variation of the optical anisotropy are briefly discussed.
ABSTRACT 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 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 , using multiple‐reflection theory, terminated at the second reflection. The attenuation values can be estimated independently by means of the electromagnetic parameters obtained using an LCR meter. To compare and , an effective TDR frequency 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 and values for magnetite/glass‐beads mixtures, which simulate dry soils with increasing iron oxides content, are reported and discussed.
Time domain reflectometry (TDR) measurements, performed in a cylindrical tube filled with air, glass beads, and water, are analyzed in the time and frequency domains. In the time domain, air and water provide contrasting results of the probe length if the standard tangent line fitting procedure is used. An alternative method, based on the time derivative of the TDR response, is introduced. Its application suggests that the anomalous result provided by the tangent method in water is explained by dispersion effects. To account for the frequency dependence of the permittivity, an analysis in the frequency domain is performed. The problems of the input function choice and of the noise control are investigated. This allows us to correct the experimental scatter function S (ν) and to perform the best fit of its parameterized expression, which is theoretically evaluated from the Debye model of the permittivity. Consistent values of the probe length are derived. It is concluded that the tangent method cannot be applied for determining the geometrical and electromagnetic parameters of a probe filled by dispersive media. As an application, the calibrated probe is used for measuring the TDR trace of glass beads, which simulate sandy soils, and for deriving the frequency‐dependent permittivity within the Debye model.
We explore a new approach to evaluate the effect of soil electromagnetic parameters on early-time ground-penetrating radar (GPR) signals. The analysis is performed in a time interval which contains the direct airwaves and ground waves, propagating between transmitting and receiving antennas. To perform the measurements we have selected a natural test site characterized by very strong lateral gradient of the soil electrical properties. To evaluate the effect of the subsoil permittivity and conductivity on the radar response we compare the envelope amplitude of the GPR signals received in the first [Formula: see text] within [Formula: see text]-wide windows, with the electrical properties ([Formula: see text] and [Formula: see text]) determined using time-domain reflectometry (TDR). The results show that the constitutive soil parameters strongly influence early-time signals, suggesting a novel approach for estimating the spatial variability of water content with GPR.
