An inversion method for geometric and electric parameters of layered media using spectrum of GPR signal

The generalized reflection coefficients of underground layered media for Ground Penetrating Radar (GPR) wave are defined and a pair of the coefficient of three-layer media is decomposed into the even component and the odd one. A cost function is established to connect the spectrum of reflection coefficient sequence with the layer's parameters, which include position of reflection interfaces, layers' thickness, dielectric permittivity and electric conductivity. Then a global optimal inversion method is proposed for multiple parameters of underground layered media from GPR signal spectrum. Moreover, through the research on the effects of different parameter on the spectrum of reflection coefficient sequence, a method for estimation of different parameter from different spectral attributes is proposed, namely staged inversion method. The result of the staged inversion was used as the starting value for the global inversion, the efficiency and accuracy of which were then improved greatly. The methods in this paper were tested using synthetic and observed data, and good results of layer thickness, interface position and electric properties were obtained, even when thickness of the layer is less than tuning thickness.