Reliable quantitative characterization of subsurface thin layers is impossible using standard reflection data processing techniques, e.g. velocity analysis, if the layer thickness is below the conventional resolution limits of the data. The limiting layer thickness for such resolution is approximately one-half the dominant wavelength of the signal in the medium of interest. In many environmental problems, target layers are below this layer thickness; and accurate determination of layer properties becomes problematic. In spite of the difficulty, site managers and scientists need ways to reliably quantify thin layer parameters for problems such as contaminated site investigation and subsequent remediation efforts, oil spill detection in Arctic conditions, and determination of basal conditions in mountain glaciers. I propose to use radar and seismic data in conjunction with amplitude variation with offset (AVO) analysis to determine thin-layer characteristics for these three examples and several others. In addition, as part of this research, I will also develop and implement a full-waveform inversion algorithm to estimate the thin-layer parameters of interest. When complete, these processing methodologies and the inversion improve our ability to characterize thin subsurface layers, which was previously difficult or impossible.