Using Ground Penetrating Radar to Reveal Hidden Archaeology: The Case Study of the Wxc3xbcrttembergStambol Gate in Belgrade (Serbia) This paper presents the results of a research study where ground penetrating radar (GPR) was successfully used to reveal the remains of the WurttembergStambol Gate in the subsurface of Republic Square, in Belgrade, Serbia. GPR investigations were carried out in the context of renovation works in the square, which involved rearranging traffic control, expanding the pedestrian zone, renewing the surface layer, and valorising existing archaeological structures. The presence of the gate remains was suggested by historical documents and information from previous restoration works. A pulsed radar unit was used for the survey, with antennas having 200 and 400MHz central frequencies. Data were recorded over a grid and two threedimensional models were built, one for each set of antennas. The grid was the same for both sets of antennas, therefore the two models could be compared. Several horizontal cross sections of the models were plotted, corresponding to different depths; these images were carefully examined and interpreted, paying particular attention to signatures that could originate from the sought archaeological structures. Reflections coming from the gate remains were identified in both models, in the same region of the survey area and at the same depth; the geometry, size, and layout of the gate columns, as well as of other construction elements belonging to the gate, were determined with very good accuracy. Based on the GPR findings, archaeological excavation works were carried out in the region where the foundation remains were estimated to be. The presence of the remains was confirmed, with various columns and side walls. This case study demonstrates and further corroborates the effectiveness and reliability of GPR for the noninvasive prospection of archaeological structures hidden in the heterogeneous subsurface of urban environments. In the opinion of the authors, GPR should be incorporated as a routine field procedure in construction and renovation projects involving historical cities.

3D modeling of groundpenetrating radar data across a realistic sedimentary model Abstract   Groundpenetrating radar (GPR) is an established geophysical tool to explore a wide range of nearsurface environments. Today, the use of synthetic GPR data is largely limited to 2D because 3D modeling is computationally more expensive. In fact, only recent developments of modeling tools and powerful hardware allow for a timeefficient computation of extensive 3D data sets. Thus, 3D subsurface models and resulting GPR data sets, which are of great interest to develop and evaluate novel approaches in data analysis and interpretation, have not been made publicly available up to now.  We use a published hydrofacies data set of an aquiferanalog study within fluvioglacial deposits to infer a realistic 3D porosity model showing heterogeneities at multiple spatial scales. Assuming freshwater saturated sediments, we generate synthetic 3D GPR data across this model using novel GPUacceleration included in the opensource software gprMax. We present a numerical approach to examine 3D wavepropagation effects in modeled GPR data. Using the results of this examination study, we conduct a spatial model decomposition to enable a computationally efficient 3D simulation of a typical GPR reflection data set across the entire model surface. We process the resulting GPR data set using a standard 3D structural imaging sequence and compare the results to selected input data to demonstrate the feasibility and potential of the presented modeling studies. We conclude on conceivable applications of our 3D GPR reflection data set and the underlying porosity model, which are both publicly available and, thus, can support future methodological developments in GPR and other nearsurface geophysical techniques.