To provide a database for interpreting GPR field data by means of small-scale laboratory studies, we have determined the real and imaginary parts of the dielectric permittivity of fine-grained fractions of soil samples from eastern Spain in the laboratory. We use the parallel-plate method in combination with an impedance analyzer and focus on the frequency of [Formula: see text]. The measurements are compared to physical properties such as volumetric water content, dry density, clay fraction, and carbonate content. The results show the well-known increase in dielectric permittivity with increasing water content, as presented in the literature; however, our values are systematically higher. This deviation may be caused by the exceptionally high carbonate content of the samples. We establish a basic relationship between dielectric permittivity and water content that is characteristic for soils in the research area. In addition to the dominating influence of water on permittivity, we find a correlation with dry density as well, which is linear for dry samples. Finally, we calculate the attenuation coefficients and find high attenuation for samples with high clay fraction, even at low water contents. A 1D model of the permittivity distribution is constructed from borehole data (water content and layer thickness) coincident with a GPR profile and from the laboratory data. The modeled GPR trace explains the observation and thus connects laboratory measurements to GPR data.
Airborne ground penetrating radar (GPR) measurements of temperate ice are a challenge because of absorption, internal scattering, and surface roughness. We found that at center frequencies of 30 MHz or below effects of scattering and roughness are sufficiently reduced to produce good quality radar data. The 30 MHz helicopter radar system BGR-P30 is able to penetrate temperate ice to more than 700 m depth. In 2010 about 220 km of GPR profiles were obtained by helicopter measurements performed on flight patterns over Nef and Colonia glaciers in Patagonia, Chile. We report the technique, processing, and results of these novel ice thickness measurements.
The most important parameter affecting ground-penetrating radar (GPR) measurements is the complex effective relative permittivity * r,eff ε because it controls the propagation velocity and the reflection of GPR pulses. Knowing * r,eff ε of soils passed through by electromagnetic waves increases accuracy in soil thickness and interface identification. Complex effective relative permittivity * ' ' ' r,eff r,eff r,eff j ε ε ε = − of 25 soil samples with textures ranging from loamy sand to silty clay was measured using the two-electrode parallelplate method. The measurements were conducted at defined water contents for frequencies from 1 MHz to 3 GHz. The results confirm the frequency dependence of * r,eff ε and show that the dielectric behavior of soil-water mixtures is a function of water content. Applying the experimental data of this study with predictions based on the empirical model by Topp et al. (1980), we find that Topp et al.'s curve tends to underestimate the real part of * r,eff ε measured. Along with frequency and water content, soil texture and organic matter affect soil permittivity. Moreover, the real part of * r,eff ε increases at higher dry bulk densities. Output from our calibration model enables us to predict * r,eff ε for the soil samples which were tested under the actual in situ soil water content. This results in high accuracy of soil thickness prediction.KEY WORDS: ground-penetrating radar (GPR), complex effective relative permittivity, soil sample.
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