MODELLING PERMITTIVITY FOR THE APPLICATION OF GPR FOR DETECTING BURIED PREHISTORIC ANIMAL BONES

This research explores the use of ground-penetrating radar (GPR) to detect buried prehistoric animal bones. In order to evaluate the application of GPR for detecting buried animal bones in different environmental settings, the electrical properties of bone must be understood, in particular the relative permittivity of the bone. Previously, results of the electrical properties (relative permittivity, loss factor, and loss tangent) of five animal species, including modern cow, bison, deer, elk, and prehistoric mammoth were presented in the frequency ranges of 10 MHz to 1 GHz. Bone-sample porosity, bulk density, water saturation and volumetric water content of the modern bone specimens were also measured. Results showed statistically significant electrical property differences among different animal fauna, as well as a decrease in permittivity as a function of increasing frequency. The differences observed between the mean values of the permittivity of different species is significant and indicates that assuming one range of permittivity values at varying frequencies for all bone is not accurate and can affect ground-penetrating radar modelling parameters. In addition, porosity and water saturation levels of the bones at the time of measurement also need to be considered for accurate modelling of the relative permittivity of the sample.

This paper presents a comparison of measured bone permittivity values to modeled permittivity values using the complex refractive index model (CRIM). CRIM is a commonly used relative permittivity mixing model that accounts for the heterogeneity of a material by including the effects of sample porosity, water saturation and sample material permittivity. The CRIM model was used in order to estimate relative permittivity values of the bone mineral grain of each animal type. Overall, we found that the CRIM model was effective for the entire frequency range of 10 MHz to 1000 MHz and that the relative permittivity values of the bone mineral grains range from 3-5 across the four species. The deer and elk bone mineral values were lower than the bison and cow bone mineral values, which is consistent with the results of the measured permittivity values.