*3.5. GPR Tomographic Imaging of Floor*

Figure 21 presents the tomographic images of the south aisle. At the depth of 0.16 m (Figure 21a), the tombstones identified in the above-discussed B-scans of the south aisle were detected. The elements were laid in a straight line along the whole aisle at the width between about 2.75 and 4.25 m. Additionally, the single tombstone was located aside from the main row at the length between 2.5 and 4.5 m (it was seen in the A-129 scan, Figure 19). The distinction of singular tombstones from the main row was not possible; the scanning was performed along the tombstone grouts, thus they could not be

imaged. The singular tiles were not detected due to a single direction profiling. The tile grouts in the lengthwise direction (perpendicular to the measurement traces) were identified, unlike the crosswise grouts (oriented in the same direction as the scan traces). At the depth of 4.06 cm (Figure 21b), the imaging of the tombstones was far clearer; however, there was still no possibility to distinguish the singular elements. On the contrary, the individual tiles could be detected; the chosen tomography depth was between the minimum and the maximum thickness of the tiles, thus some of them were visible, whereas other ones could not be observed. At the depth of 12.19 cm (Figure 21c), most of the tombstones were clearly visible. The lower faces of some thicker tombstones were below the tomography depth, unlike the thinner ones, which were not detected at this level. The adornment was detected on the second tombstone from the left. The tiles could not be identified because their bottom faces were located certainly above the actual tomography level. What is more, the brick wall was moderately imaged at the width of about 5.2 m and the length between 2.2 and 13.8 m. The tombstones were still distinguishable at the depth of 23.75 cm (Figure 21d). The inhomogeneities in the ground under certain tombstones were visible, especially on the right side of the tomography. The brick wall discovered at the depth of 12.19 cm was still detectable and seemed to be longer. What is more, another two brick walls were identified: the first one at the width of 4.5 m and the length between 5.5 and 14.0 m, the second at the width of 2.2 m and the length between 6.5 and 15.0 m. All of the three walls were clearly imaged in the A-117 B-scan (see Figure 17b).

Figure 22 shows the tomographic images of the north aisle. Similarly to the results for the south aisle, the tombstones were detected at the depth of 0.16 cm (Figure 22a); however, their configuration was not so regular. The lengthwise tile grouts were also imaged, unlike the crosswise grouts. The adornments were visible on some of the tombstones. At the depth of 4.06 cm, the tombstones were shown far more clearly. Some individual tiles were also observed. At the depth of 12.19 cm, the singular tombstones could be distinguished. Some of them did not seem to be rectangular because of the irregular shape of their bottom faces. It is also worth noting that the staircase reinforcement was visible at the length of 30.0–32.0 m and the width of 5.2–7.8 m. Only the lengthwise bars were noticeable, and the crosswise reinforcement could not be imaged because of the single direction of the GPR scanning.

**Figure 21.** GPR tomographic images of the south aisle (survey A) at different depths: (**a**) 0.16 cm; (**b**) 4.06 cm; (**c**) 12.19 cm; (**d**) 23.75 cm.

**Figure 22.** GPR tomographic images of the north aisle (survey B) at different depths: (**a**) 0.16 cm; (**b**) 4.06 cm; (**c**) 12.19 cm.
