Pronounced dispersion of ground-penetrating radar (GPR) waves is observed at locations distinguished by thin surface layers of high-permittivity material (e.g., water-saturated soil). The dispersion characteristics depend on the permittivity and thickness of the effective surface waveguide and the permittivity of the material below it. We introduce a scheme for estimating the values of these parameters from dispersed transverse-electric (TE) and transverse-magnetic (TM) GPR data that is analogous to recently developed methods for analyzing dispersed Rayleigh waves recorded on multichannel seismic data. Our scheme involves calculating phase-velocity spectra, picking dispersion curves from the spectra, and then inverting the dispersion curves for the subsurface material properties by using a combined local- and global-minimization procedure. Application of this new scheme to synthetic and field data demonstrates its efficacy in providing the required physical property information. Where the surface layer is relatively distinct and uniform, inversions of the resulting high-quality dispersed TE data provide all required parameters. In more heterogeneous environments, joint inversions of the TE and TM data, which usually include information in different frequency ranges, may be required.