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Due to several sources of multipath in through-wall radar sensing, such as walls, floors, and ceilings, there could exist multipath ghosts associated with a few genuine targets in the synthetic aperture beamformed image. The multipath ghosts are false positives and therefore confusable with genuine targets. Here, we develop a multipath exploitation technique using point spread functions, which associate and map back the multipath ghosts to their genuine targets, thereby increasing the effective signal-to-clutter ratio (SCR) at the genuine target locations. To do so, we first develop a multipath model advocating the Householder transformation, which permits modeling multiple reflections at multiple walls, and also allows for unconventional room/building geometries. Second, closed-form solutions of the multipath ghost locations assuming free space propagation are derived. Third, a nonlinear least squares optimization is formulated and initialized with these free space solutions to localize the multipath ghosts in through-wall radar sensing. The exploitation approach is general and does not require a priori assumptions on the number of targets. The free space multipath ghost locations and exploitation technique derived here may be used as is for multipath exploitation in urban canyons via synthetic aperture radar. Analytical expressions quantifying the SCR gain after multipath exploitation are derived. The analysis is validated with experimental EM results using finite-difference time-domain simulations.

The development of cracks and distortions caused by past seismic events compromised the integrity of the rose window of Troia Cathedral, one of the most precious Romanesque monuments in southern Italy. Ground-penetrating radar (GPR) using high-frequency antennae (mainly 1500 MHz) was selected from among various non-destructive testing methods for its high-resolution imaging to scan the internal structure of the various architectural elements of the wheel window: the decimetre-diameter columns constituting the rays, the ring decorated with intersecting arched ribwork and the surrounding circular ashlar curb. GPR was employed in the classical continuous reflection mode, moving the antennae manually along the architectural elements and paying exceptional care in the acquisition and processing stages to avoid positioning errors. Indeed, the challenging aspects of this case study were the geometrical complexity and small dimensions of the structural elements, causing many logistic/coupling problems. In spite of this, through proper interpretation techniques, based on signal analysis (presence of reflections and diffractions, velocity and attenuation variations) and correlation with features detected by visual inspection of the external surfaces, the GPR survey provided useful information on the internal structure of the rose window, detecting fractures and the boundaries of previously restored parts and locating hidden metallic components connecting the architectural elements. Information on the internal structure and spatial distribution of metallic junctions was essential for gaining insight into building techniques in order to discriminate between restoration strategies which may require either total or partial dismantling of the rose window. GPR results provided crucial evidence in favour of one of the (conflicting) hypotheses about the original building techniques, leading to the selection of partial dismantling as the most suitable restoration strategy. Analysis of measurements revealed the potential of GPR in the field of cultural heritage restoration, even in those cases characterized by complex geometry, structural brittleness and logistic difficulties, such as that discussed in this paper.

Hierapolis, Denizli, Turkey, was one of the most important Hellenistic-Roman cities in Asia Minor.Located about 250 km east of Izmir, the area is a UNESCO World Heritage Site because of its magnificent archaeologicalremainsandthewhitetravertine poolformationscreated byitspeculiargeothermal setting. The Italian Archaeological Mission in more than 50 years of activity in Hierapolis has brought to light and restored important vestiges of the ancient city, helping to understand the urban layout in the various epochs of its development. In 2001^2003 geophysical surveys were performed by the University of Lecce in several areas inside the archaeological site of Hierapolis to support the archaeological excavations.This paper reports the results of the integrated geophysical surveys performed in 2003 inside the Martyrium of Saint Philip, a mausoleum built on the place where it is believed that the Apostle was martyred. Ground-penetrating radar (GPR), electrical resistivity tomography (ERT) and magnetic gradient investigations were carried out in the central octagonal room, whereas the accessible lateral rooms were surveyed with GPR and occasionally ERT.The acquisition was performed along a series of closely spaced lines and the processed data were visualized as two-dimensional vertical sections (GPR), map view (magnetic gradiometry), depth slices or threedimensional volumes (GPR and ERT) to allow an integrated interpretation of the geophysical results. The analysis of the geophysical datasets revealed a series of anomaliesin both the central andlateral rooms that could be ascribed to the building foundations and to other possible archaeological structures, probablyrelated to earlier stagesofthe sacredbuildingandto tombs, aswellasotheranomalies (voids, fractures) of presumable natural origin.