Using Ground Penetrating Radar to Reveal Hidden Archaeology: The Case Study of the Württemberg-Stambol 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 Württemberg-Stambol 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 The presence of the gate remains was suggested by historical documents and information from previous restoration works.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 400-MHz central frequencies. Data were recorded over a grid and two three-dimensional 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 non-invasive 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.

Through-wall electromagnetic scattering by N conducting cylinders.

A spectral-domain analysis is presented for the scattering by perfectly conducting cylindrical objects behind a dielectric wall. The solution is developed with an analytical-numerical technique, based on the cylindrical wave approach. Suitable cylindrical functions and their spectral representations are introduced as basis functions for the scattered fields, to deal with their interaction with the planar interfaces bounding the wall. The numerical solution is given in TE and TM polarizations states, and in both near- and far-field zones. The model yields an accurate computation of direct scattering that can be useful for through-wall-imaging applications. A stack of three different dielectric media is considered in the theoretical model. In the numerical results, the upper medium, where the incident field is generated, is assumed to be filled by air, the central layer represents the wall, and the lower medium, which contains the scatterers, is air filled, too. Also general problems of scattering by buried objects can be simulated, being the cylinders buried in a medium of arbitrary permittivity, placed below a dielectric layer.

Spectral domain method for the electromagnetic scattering by a buried sphere.

A rigorous method to analyze the electromagnetic scattering of an elliptically polarized plane wave by a sphere buried in a dielectric half-space, is presented. The electric field components of the incident and the scattered monochromatic plane waves are expanded in series of vectorial spherical harmonics, with unknown expansion coefficients. The scattered-reflected and scattered-transmitted fields are computed by exploiting the plane-wave spectrum of the scattered field, considering the reflection and transmission of each elementary plane wave by the interface. The boundary-condition imposition leads to a linear system that returns the unknown coefficients of the scattered field. To achieve a numerical solution, a code has been implemented, and a truncation criterion for the involved series has been proposed. Comparisons with the literature and simulations performed with a commercial software are presented. A generalization of the method to the case of a short pulse scattered by a buried sphere is presented, taking into account the dispersive properties of the involved media.

Scattering by dielectric circular cylinders in a dielectric slab.

An analytical-numerical technique for the solution of the plane-wave scattering problem by a set of dielectric cylinders embedded in a dielectric slab is presented. Scattered fields are expressed by means of expansions into cylindrical functions, and the concept of plane-wave spectrum of a cylindrical function is employed to define reflection and transmission through the planar interfaces. Multiple reflection phenomena due to the presence of a layered geometry are taken into account. Solutions can be obtained for both TM and TE polarizations and for near- and far-field regions. The numerical approach is described and the method is validated by comparison with examples given in the literature, with very good agreement. Results are presented for the scattering by a finite grid of three cylinders embedded in a slab.