Two-layer inversion of dispersive GPR data due to freezing induced waveguides — A synthetic study

A large permittivity contrast between a thin surface layer and the underlying substratum, caused by rapid changing dynamic processes in the subsurface, can result in waveguide dispersion. In some cases, a single-layer waveguide cannot explain the measured electromagnetic waves. Here, we show an analysis of four synthetic dispersive datasets of two-layer leaky waveguides which have large and small permittivity contrasts between the layers as well as an increasing and a decreasing permittivity with depth. The four synthetic datasets are inverted with a multi-layer inversion algorithm for leaky waveguides and with different single-layer inversion algorithms. For the two-layer waveguides with a large increasing permittivity with depth, it is not possible to reliably reconstruct the model parameters of the lowest layer. For small contrasts within the waveguide, the single-layer inversion algorithm resulted in an arithmetic mean value for the permittivity and a total waveguide thickness.