## 4 Results and Discussion
### The Herculane Dam Data  
Unsurprisingly, the character and the type of anomalies are significantly different at the concrete arch dam, Herculane. After processing the data, it appears that both profiles which were closer to the edge of the dam fail to provide useful reflections, most probably due to the raised kerb and proximity to the fence. Therefore, the focus remains only on the central profile from both data sets. The first data set, S1 (Figure 12), which has a low-pass and a high-pass filter applied, as well as a negative gain on the top layer with higher gain applied with depth, and a high stacking number (Table A1), appears to offer information from approximately down to 9 m. The velocity for the migration was calculated based on hyperbola fitting, and uses a value of 0.1 m/ns. The profiles have also been cut to extract information only from specific portions of the dam due to the increased number of metallic elements on the surface and the high effect on the data of the spillway area. Even though a multitude of reflections are visible at the top of the profile (Figure 12--AOI 1), ranging between 10 and 20 ns, these do not appear as strong as the reflections in the second data set (Figure 13--up). The second data set, S2, which has no stacking, no function gain, and no filters applied to the raw data at the acquisition stage, offers a better view at the small continuous reflections in that layer, managing to offer more information regarding the intensity of the reflections as well. For example, in the area marked as AOI 4 (Figure 13--up), these reflections appear less intense, with the AOI 5 slightly more intense compared to the almost non-visible ones in AOI 4. Those marked as AOI 5 (Figure 13--up) represents a distinct area that is almost unique compared to the rest of the profile. In this area, the reflections are probably the strongest. In both data sets, marked as BM with green arrows, significant metallic reflections are represented by reverberation underneath, appearing more intense in the second data set (Figure 13--up). However, even though the second data set, S2, provides enough detail, the useful information marked by reflections appears to stop at about 90 ns (Figure 13) compared to the data from the first set, S1 (Figure 12); therefore, it does not offer information about the area marked with yellow rectangle named AOI 2 in the first data set (Figure 12). This area is represented by what can be described as an inhomogeneous character compared to the background, with a multitude of reflections with higher intensity. Figure 11: Leveling data measured at the benchmarks from the dam’s crest, as described by [PERSON] et al., 2017 [44] using data from Table A3. The orientation of the graph matches the orientation of the GPR profiles. Figure 12: Processed data from the set 1 (S1). Up—profile H1; down—H1 profile with migration applied. Figure 13: Processed data from the second data set, S2. Up—profile H1; down—profile H1 with migration applied. At the Herculane dam, only the central profile (H1) profile provided useful data, as the fence and raised concrete substantially affected the quality of the data and rendered it largely useless. The data collected in two different data sets (S1-S2) with two different acquisition parameter settings managed to complement each other into providing more information, compared to using individual data sets, even when using the same antenna frequency. The second data set at the Herculane dam, S2, manages to image the top layer of the dam, highlighting reflections indicative of rebars, marked as AOI3 at the top (Figure 10). The rebar reflections may provide some information regarding the state of the rebars themselves or their surrounding environment. For instance, the rebars in the area marked as AOI3 (Figure 13--down) show strong reflections that appear indicative of good quality rebars, whereas the rebars in the areas marked as AOI4-5 show a reduced intensity of reflection, which may be indicative of water which lowers the speed of wave propagation [43].