Complex permittivity of karst medium in frequency domain and attenuation characteristics of ground penetrating radar signal

Mastering the dispersion and attenuation characteristics of ground-penetrating radar (GPR) electromagnetic waves in karst media is fundamental for identifying unfavorable karst geological bodies using attribute parameters. In this study, the frequency-domain complex permittivity of typical karst media in Guangxi was tested using a vector network analyzer. The dispersion parameters were fitted and solved through a second-order Debye model, and the dispersion-attenuation behavior of GPR waves was simulated via the finite-difference time-domain (FDTD) method. The reliability of the simulation was validated through physical model tests. Results demonstrate that the real and imaginary parts of the complex permittivity of saturated marl were higher than those of limestone and dolomite, with the most significant decline observed as frequency increased. The complex permittivity of clay fillings correlated with parent rock lithology, moisture content, and karst water mineralization. Both real and imaginary part increased with rising moisture content, while mineralization exerted a more pronounced influence on the imaginary part. GPR wave amplitudes decreased with higher moisture content and mineralization in clay fillings, while peak frequencies showed negligible variation with moisture content but decreased with elevated mineralization. Attenuation coefficients and quality factors effectively characterized the amplitude and peak frequency attenuation mechanisms. Engineering case studies confirmed consistency between forward-modeled GPR signal attenuation characteristics and field measurements. This research provides a theoretical foundation for identifying unfavorable karst geological bodies based on attribute analysis./t/n.Keywords: ground penetrating radar; complex dielectric constant; karst; forward simulation; dispersion attenuation.