A new inversion scheme for common-offset ground-penetrating radar measurements at multiple antenna separations was proposed, which is intermediate between inverting of picked reflectors using ray-tracing and full-waveform inversion. The measurements are modeled similarly to the real data using 2D finite-difference time-domain simulations. These simulations are obtained with a parameterized model of the subsurface that consists of several layers with constant dielectric permittivity and an explicit representation of the layers' interfaces. Then, reflections in the modeled and in the real data are detected automatically, and the reflections of interest of the real data are selected manually. The sum of squared residuals of the reflections' traveltime and amplitude is iteratively minimized to estimate subsurface water content and geometry, i.e., the position and shape of the layer interfaces. The method was first tested with a synthetic data set and then applied to a real data set. The comparison of the method's result with ground-truth data showed an agreement with the subsurface geometry within ±5 cm and with the water content, a difference less than ±2% volume.