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Journal of Archaeological Science 40 (2013) 4162e4169

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Journal of Archaeological Science

journal homepage: http: / /www.elsevier .com/locate/ jas

The mosaic of the crypt of St. Nicholas in Bari (Italy): integrated GPRand laboratory diagnostic study

A. Calia, M. Lettieri, G. Leucci*, L. Matera, R. Persico, M. SileoInstitute for Archaeological and Monumental Heritage (IBAM) e National Research Council (CNR), Prov.le Lecce-monteroni, 73100 Lecce, Italy

a r t i c l e i n f o

Article history:Received 7 February 2013Received in revised form25 April 2013Accepted 6 June 2013

Keywords:GPRLaboratory analysisCrypt of St NicolaMosaic

* Corresponding author. Tel.: þ39 (0)832422223.E-mail address: g.leucci@ibam.cnr.it (G. Leucci).

0305-4403/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.jas.2013.06.005

a b s t r a c t

The crypt of St. Nicholas in Bari, Southern Italy, is a building of cultural worldwide importance. Inside thecrypt a mosaic develops on the apsidal floor and along a parietal seat placed along the apsidal masonry,in the form of cladding. A surviving portion of the mosaic pavement is also preserved in the right lateralchapel. Integrated non-destructive survey and laboratory analyses were undertaken for the diagnosticstudy of the mosaic. GPR prospection was successfully applied to the study of its conservation state, thatis strictly related to the condition of the subsoil, in particular to the presence and distribution of water.The presence of water, whose rise interests also some portions of the masonry and water content dis-tribution were identified by the results of electromagnetic wave velocity analysis in GPR data.

The decay visible on the tesserae evidenced widespread spalling and crumbling as typical forms thatselectively affect the different materials of the tesserae of the mosaic. Samples taken from them wereinvestigated by optical microscopy, X-ray diffraction, ion chromatography, infrared spectroscopy andthermogravimetric analyses, in order to identify the constituent materials and the products of their decay.

The application of the integrated methodologies showed its effectiveness in order to acquire a quitecomplete knowledge for diagnostic purpose. Decay appeared to be due to the combined presence ofwater and soluble salts and it has different effects depending on the materials characteristics.

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1. The case history

The Basilica of St Nicholas is located in the town of Bari, Italy, onthe Adriatic sea (see Fig. 1), and originally was not a church. Inparticular, around the year 1000, when a large part of southern Italywas enclosed in the Byzantine Empire, the Basilica was the resi-dence of the Byzantine governor, which made Bari an importanttown from a political and economical point of view. However, in1071 the Normans conquered this area, and a series of politicalevents subsequent to this conquest (whose details of course areavoided) eventually made Bari quite marginal and peripheral withrespect to the role it used to have during the Byzantine period. Togive back to Bari at least part of the ancient renown, in 1087 somepeople organized the theft of the relics of St. Nicholas, treasured inMyra, a town on the sea in Southern Turkey. At that time, in fact, tohave the relics of a venerated Saint had a political and economicalimportance, also due to the pilgrimages that the relics used toattract. The theft was successful, and so the old building of theBasilica was partially demolished and rebuilt, and was consecratedas a church in order to hedge in the relics of St. Nicholas. The

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Basilica is a complex and “sombre” Romanesque style monument,partially decorated by re-employing precedent Byzantine materialsandwith several modifications and further re-decorations occurredduring the centuries. For a detailed description of the architectureof the church, we refer the interested reader to the official site ofthe Basilica http://www.basilicasannicola.it/. Here, it is importantto outline that, beyond having an important historical and artisticvalue, the Basilica is still nowadays the destination of many pil-grimages, because St. Nicholas is venerated both by catholic be-lievers inwestern Europe and orthodox believers in eastern Europe(let us just remind that the schism between the two Churchesoccurred in the year 1057, i.e. seven centuries after the death of theSaint). In particular, nowadays both catholic and orthodox Massesare celebrated in the crypt of the Basilica. This makes this Basilica avery important monument, because it is a place with a meaningfulsymbolic value within the modern ecumenical reconciliation pro-cess started from the Second Vatican Council (1962e1965) and stillgoing on within the Christianity.

2. Monument analysis: integration of methodologies

Geophysical investigation in monumental buildings is animportant issue, because it is able to provide both historical and

Fig. 1. Basilica of St. Nicholas in Bari (Italy).

A. Calia et al. / Journal of Archaeological Science 40 (2013) 4162e4169 4163

structural information about the monument at hand (Barone et al.,2010; Bavusi et al., 2008; Binda et al., 2003, 2004; Kadioglu andKadioglu, 2010; Leucci et al., 2011, 2012a,b; Pieraccini et al., 2004;Ranalli et al., 2004; Utsi, 2010).

[1] In particular, issues of structural interest are the possiblepresence of fractures, voids, infiltrations of humidity ormetallic bars due to previous restoration works. Incidentally,these might date back to centuries ago and often are notdocumented. These investigations are well advised especially ifrestoration works are scheduled, both to give an insight foraddressing them and to provide a check about their effects bymeans of a post intervention monitoring. Issues of historicalinterest might be the presence of tombs, walled rooms, hiddenpictures, mosaics and floors (Grasso et al., 2011). In fact, thechanges to which the building underwent during the centuriesin many cases were not documented, or in other cases thedocuments have been lost. In some cases, the valence of aretrieved buried target can be twofold, i.e. both historical andstructural, as e.g. in the case of a hidden Crypt under a church.

[2] Historical buildings present some favourable aspects for GPRand other geophysical techniques, mainly because in thesecases one usually works on smooth surfaces and, of course,man-made structures, which customarily mitigates the prob-lem of the roughness of the interface. Moreover, the fact thatthe measurements are performed (often, even if not ever) in-door presents some obvious logistical advantages too. On theother hand, some structural elements, as pillar, columns, archesand so on, show curved surfaces (as in the present casestudy) and are not rigorously tractable with the usual methodssuited for flat interfaces (Binda et al., 2004; Nuzzo and Quarta,2010; Docherty, 1991; Stolt, 1978; Persico et al., 2005; Leucciet al., 2007). Indirect investigations, such as the GPR pro-specting, can give a general representation of the conditions ofthe structure and can give an insight about some parametersrelevant to the decay condition, as e.g. the water content(which is of interest in the present case study). However, a

complete and punctual diagnosis concerning the causes andthe effects of the decay requires an integration with laboratoryanalyses that allow to gain additional knowledge otherwise notavailable. Of course, a limit for the laboratory analyses isrecognized in their intrinsic destructivity, but nevertheless theimpact of the sampling can be minimized by a suitable andcareful choice of the most significant sampling points. A pre-liminary general representation of the decay context, obtainedfrom both non-destructive large scale investigations and in situpreliminary surveys should undoubtedly contribute to reducethe invasiveness of the sampling.

With regard to the present case history integrated non-invasivegeophysical investigation and optical microscopy, X-ray diffraction(XRD), ion chromatography, infrared spectroscopy (FTIR) andthermogravimetric analyses (TG-DSC), were undertaken on themosaic inside the crypt (Fig. 2) in order to identify the causes ofdeterioration, the constituent materials and the products related totheir decay.

The results show an interesting integration between the dataobtained by the GPR method and laboratory analyses. It is thusdemonstrated the existence of a direct correlation between thedeterioration of the mosaic and water presence.

3. GPR data acquisition and analysis

The GPR survey was carried out with a Hi Mod system using the2000 MHz (centre frequency) antenna manufactured by IDS. Thefollowing acquisition parameters were selected: i) samples perscan: 512; ii) _ recording time window: 20 ns; iii) gain function:manual; iv) reference marks distance: 0.2 m. In order to obtain a 3Dmodel of the mosaic, one should make an adequate field acquisi-tion; consisting of a grid of GPR lines. Hence the surveyed area onthe wall was a curved rectangle sized 12 � 0.8 m. Parallel GPR lineswere performed spaced 0.05 m apart (Fig. 2).

The quality of the original data required an appropriateprocessing for easier interpretation. Processing steps can be

Fig. 2. The mosaic inside of the crypt of St. Nicholas with location of GPR profiles.

A. Calia et al. / Journal of Archaeological Science 40 (2013) 4162e41694164

summarized as follows using reflex software (Sandmeier, 2012;Leucci et al., 2007): i) amplitude normalization; consisting of thedeclipping of saturated (and thus clipped) traces by means of apolynomial interpolation procedure; ii) background removal; thefilter is a simple arithmetic process that sums all the amplitudes ofreflections that were recorded at the same time along a profile anddivides by the number of added traces. The resulting compositedigital wave is then subtracted from the data set; iii) Kirchhoff 2D-velocity migration; a time migration of a two-dimensional profileon the basis of a 2D-velocity distribution is performed. The goal ofthe migration is to trace back the reflection and diffraction energyto their ‘‘source’’. The Kirchhoff 2D-velocity migration is done in theset range; this means that a weighted summation for each point ofthe profile over a calculated hyperbola of preset bandwidth isperformed. iv) topographical correction due to the semi circularshape of the antenna’s path (Fig. 2).

A general characteristic of the surveyed area is a good pene-tration of the electromagnetic energy (about 15 ns correspondingto a depth of about 0.5 m if the mean velocity value of 0.07 m/ns isused); it is essentially due to the physical characteristics of thesubsurface which is characterized by low-loss material. Most of theobserved anomalies are confined from 0 to 15 ns (Fig. 3).

The shape and alignment of the anomalies found in the sur-veyed area suggest that they could be related to the probablepresence of deterioration forms (such as fractures and voids).

3.1. Electromagnetic wave velocity measurements

The electromagnetic (EM) wave velocity plays an important rolein defining the depth of the archaeological features. EM wave ve-locity can be estimated from GPR data in several ways; the con-ventional method involves common depth-point (CDP) and wide-

angle reflection and refraction (WARR) data sets. Both methodsrequire two antennas in separate units and relatively long acqui-sition times. In the first case, both antennas are simultaneouslymoved apart on both sides of the mid-point of the profile. In thesecond case, one antenna remains stationary while the other ismoved along the profile direction. The EM wave velocity can bemore quickly and easily determined from the reflection profilesacquired in continuous mode, using the characteristic hyperbolicshape of reflection from a point source (diffraction hyperbola)(Fruhwirth et al. 1996). In the data acquired on the mosaic severalhyperbolic reflections, which allow an accurate velocity analysis,are present. The application of this method points an EM wavevelocity variation ranging from 0.06 to 0.09 m/ns.

3.2. Volumetric water content analysis

It is known that for pure water, the relative dielectric permit-tivity K is about 80, while for most dry geological material it variesbetween 4 and 10. If only a small amount of water is contained inthe material, the value of K will increase considerably and,conversely, the EM-wave velocity will decrease significantly. Thus Kis a good measure of the water-content in the ground. Severalformulae have been developed, both theoretical and empirical, togive the dielectric response of heterogeneous mixtures such aswater-saturated soils. One such formula is the complex refractiveindex method (CRIM) equation, which is often used in the inter-pretation of EM logging data (Masini et al., 2010). The majorproblemwith the CRIM formula is that it does not take into accountthe geometrical information about the internal structure of rocksand about the microscopic fluid distribution. This has a significanteffect on the dielectric properties of partially saturated rocks(Greaves et al., 1996). The above restriction may be overcome by

Fig. 3. Radar section related to R6 profile acquired on the mosaic: a) processed; b) envelope.

A. Calia et al. / Journal of Archaeological Science 40 (2013) 4162e4169 4165

using the HanaieBruggeman formula (Endrea and Knight, 1992).Themain problemwith the two previous approaches is that it is notpossible to derive both the porosity and the water-content from thedielectric constant. Therefore, it is not possible to obtain informa-tion about the water-content without strong a priori assumptions.For this reason it is preferable to use the well-known empiricalequation, derived in Topp et al. (1980), relating the dielectricresponse K of various soil samples (with different degrees of satu-ration) to their net water-content w. This formula is given by

w ¼ � 5:3� 10�2 þ 2:92� 10�2ðKÞ � 5:5� 10�4ðKÞ2

þ 4:3� 10�6ðKÞ3(1)

This equationwas found to be nearly independent of soil texture,soil bulk density, temperature and soil salinity (Du and Rummel,1994). Here, the volumetric water-content was determined fromthe dielectric properties of subsurface material, using the aboveempirical relationship (1) (Annan et al.1990; Du and Rummel,1994;Mellet, 1995; Grandjean et al. 2000; Leucci et al. 2002).

Fig. 4 shows the distribution of the EM wave velocity that couldbe transformed in volumetric water content using Eq. (1).

The greeneyellowered areas, which represents higher veloc-ities, probably corresponds to a lower soil water-content (about3.8e4.8%). The blue areas in the rest of the figure corresponds tolower velocities, and thus to a higher water-content (about 5e8%).In order towell understand the distribution of the volumetric watercontent in the surveyed area a 3D visualization was performed.Fig. 5 shows the iso-surface of volumetric water content withthreshold ranging between 6 and 8%.

4. Laboratory diagnostic analyses

The visual inspection clearly revealed different states of pres-ervation in the two sides (left and right) of the mosaic (Fig. 6).

Spalling and superficial erosion affected the reddish elementson the left side, that seem to be made of brick; both the white andthe black tesserae are compact limestones and they didn’t showevidences of decay. In this area, a white and fine powdered mortarwas found as filling material for the lacunae of some reddishtesserae. Indeed, in some points an underlying reddish brick wasobserved, as the remaining portion of the original tesserae. Someportions of the egg-shaped tesserae in the wreath decoration alsoappeared to be made of brick and they were also filled with amortar.

On the right side, the reddish decoration tesserae showed abetter state of conservation than in the left part of the mosaic. Theyappeared tobemadeof calcareous stone.Only someof themshoweda first stage of decay, consisting in detached small flakes. Theobservation of a different material used for the reddish decorationelements, along with the better state of preservation, suggested thehypothesis that this area probably underwent toworks of repairing.

Samples from the reddish elements (i.e. the red tesserae)located in either the left or the right side of the mosaic, as well asfrom the mortar filling the lacunae were taken, in order to identifythe constituent materials and the products of the decay.

The samples were first examined with a binocular microscope(Zeiss, mod. Stemi SV11) at magnifications of up to �100. This in-spection was used to observe the macroscopic features of the sam-ples in order to select the material for the analytical investigations.

Specimens were taken from these samples to prepare thin-sections, which were examined in transmitted light (StandardNorMaL 12/83, 1983; Standard NorMaL 15/84, 1984) using an op-tical microscope with polarized light (Zeiss, mod. Axioplan).

A certain amount of material was crushed into a powder andsubjected to X-ray diffraction analysis (XRD), using a Philips PW1710 diffractometer, with unfiltered CuKa radiation, and workconditions of 40 kV and 20 mA, recording the data in the 2q rangebetween 3� and 70� with a 2q step size of 0.025 and a scan step timeof 1.0 s.

Fig. 4. EM wave velocity distribution on R3 (a) and R6 (b) radar profile acquired on the mosaic.

A. Calia et al. / Journal of Archaeological Science 40 (2013) 4162e41694166

At the end of the XRD analysis, the examined powder wasdivided to perform Fourier transform infrared spectroscopy (FT-IR)analyses, simultaneous thermogravimetric and differential scan-ning calorimetric (TG-DSC) analyses, and ion exclusion chroma-tography (IC).

Fig. 5. 3D distribution of volumetric water content in

The FT-IR spectra were collected in transmission mode on KBrpellet, using a Nexus ThermoNicolet spectrophotometer; theacquisition was done in the range 4000e400 cm�1, with a resolu-tion of 4 cm�1 and 32 scans for each measurement. The TG-DSCanalyses were carried out in air flow (20 ml/min) with a heating

the mosaic: threshold ranging between 6 and 8%.

Fig. 6. The central area of the mosaic, with evidence of different states of preservation. Fig. 8. Photomicrograph of thin section from a reddish tessera on the right side.

A. Calia et al. / Journal of Archaeological Science 40 (2013) 4162e4169 4167

rate of 10 �C/min, in the range 30e1000 �C, using a NETZSCH STA449 F3 Jupiter thermobalance. A qualitative and quantitativedetermination of anions and cations of soluble salts (Standard UNI11087/2003, 2003) was made by IC; the chromatograms wererecorded with a Dionex ICS-1100 ion chromatograph (Sunnyvale);anions were analyzed using an Ionpac AG22 precolumn, an IonpacAS22 column and sodium carbonate/bicarbonate as eluent; cationswere analyzed using an Ionpac CG12A precolumn, an Ionpac CS12Acolumn and methanesulfonic acid as eluent; in both cases a SelfRegenerating Suppressor ASRS 300 was employed; the ion contentswere determined by comparison with standards of knowncomposition and for each sample at least three analyses wereperformed.

The mineralogicalepetrographical observations of the samplesconfirmed that the original reddish tesserae and egg-shaped ele-ments of the mosaic consist of bricks (Fig. 7). For the same items onthe right side an iron-rich compact limestone was identified(Fig. 8). The presence of these different materials on the two sidesof the mosaic confirmed the hypothesis that a heavy repairing ofthe mosaic was carried out by replacing the original brick tesseraeon the right part.

Fig. 7. Photomicrograph of thin section from a reddish tessera on the left side.

As regarding the material filling the lacking portions of themosaic elements, it was identified as a lime kind mortar bythe examination through optical microscopy. This finding wasconfirmed by the XRD analysis (Fig. 9) and the TG-DSC scans.Additional information was gained from this latter investigation.The constant weight decrease (not exceeding 4%), observed be-tween 200 �C and 600 �C in the TG curve (Fig. 10), could beascribed to small amounts of hydraulic compounds; however, theratio between the weight loss corresponding to the CO2 evolution(in the range 600e800 �C) and that corresponding to the H2Oevolution (in the range 200e600 �C) was higher than 10, there-fore, this material cannot be accepted as a hydraulic lime mortar(Boke et al., 2008). Moreover, it is to remark the weight loss takingplace up to 180 �C that can be ascribed to moisture and absorbedwater into the samples. A similar decrease was also noticed, fromjust above the ambient temperature (starting from 40 �C) to about100 �C, in the thermogravimetric analyses performed on the brickelements.

The degradation phenomena observed on the filling mortarand brick elements seem to be related to the presence of salts. Infact, NaCl, as halite, was identified by XRD (Fig. 9) and FT-IR

Fig. 9. XRD pattern of the filling mortar.

Fig. 10. TG and DSC curves of the filling mortar.

A. Calia et al. / Journal of Archaeological Science 40 (2013) 4162e41694168

analyses (Fig. 11) found CaSO4, as gypsum. Salt formations weredetected on thin sections observed by optical microscopy, aswell.

The presence of water-soluble salts was also detected by the ionchromatographic analyses. As reported in Table 1, high chloride andsulphate contents, along with significant amounts of sodium and

Fig. 11. FTIR spectrum acquir

potassium cations, were found in both the mortar and the bricks.These results suggest an external provenance of the salts. Giventhe high presence of sodium and potassium cations within thebrick tesserae, a contribution to the formation of salts by thealkali contained within the raw materials used for the brickmanufacturing cannot be excluded.

ed on the filling mortar.

Table 1Concentrations (% by weight) of ions from, water-soluble salts as determined by ICanalyses.

Ion [%] Filling mortar Brick elements

Cl� 1.87 � 0.02 0.19 � 0.02NO2

� e 0.07 � 0.01NO3

� 0.09 � 0.01 0.07 � 0.01PO4

2� e 0.06 � 0.01SO4

2� 0.25 � 0.01 0.18 � 0.02

Naþ 0.86 � 0.01 1.40 � 0.01Kþ 0.30 � 0.01 0.80 � 0.03Mg2þ 0.06 � 0.01 e

Ca2þ 1.95 � 0.13 0.33 � 0.02

A. Calia et al. / Journal of Archaeological Science 40 (2013) 4162e4169 4169

5. Conclusions

In this paper, the results of a prospecting performed on themosaic located inside the crypt of the Basilica of St. Nicholas in Bari(Apulia, Italy) were showed. GPR methodology allowed to identifythe damaged areas in the subsurface of the mosaic and evidencedthe 3D distribution of moisture inside the mosaic itself.

The identification of the constituent materials and their prod-ucts of decay were also achieved by mineralogical, petrographicaland chemical analyses.

The integrated interpretation of the data gathered by in situinvestigations and laboratory analyses lead to identify the causes ofthe mosaic damage. According to the results of the moisturemapping, clear evidence of penetration and rise of water from thefloor was revealed. The presence of moisture in the examinedsamples was experienced by chemical analyses, as well. In addition,significant amounts of water soluble salts were found within theconstituent materials.

It is well known that water acts as the moving agent of salts intostone materials; actually, the large water content located in themosaic was able to shift saline compounds along the back wallstowards the surface. The selective damage affecting the differenttesserae of the mosaic is consistent with a salt action whose effectsdepend on the nature of the different materials.

Finally, the identification of diverse constituent materials inseparate areas made it possible to ascertain several repairing workscarried out on the mosaic, letting us suppose that an advanceddecay affected some decorative elements in the past.

References

Annan, A.P., Scaife, J.E., Giamou, P., 1990. Mapping Buried Barrels with Magneticsand Ground Penetrating Radar, pp. 422e423, 60th SEG Meeting, San Francisco,USA, Expanded Abstracts.

Barone, P.M., Lauro, S.E., Mattei, E., Pettinelli, E., 2010. Non-destructive technique toinvestigate an archaeological structure: a GPR survey in the Domus Aurea(Rome, Italy). In: Proc. of XIII International Conference on Ground PenetratingRadar, Lecce, June 21e25. IEEE, ISBN 978-1-4244-4605-6.

Bavusi, M., Piscitelli, S., Soldovieri, F., Crocco, L., Prisco, G., Vallianatos, F., 2008.Exploitation of a microwave tomographic approach for GPR data processingcollected at historical buildings of Chania (Crete, Greece). In: Lasaponara, R.,Masini, N. (Eds.), Advances in Remote Sensing for Archaeology and CulturalHeritage Management. Aracne, Roma, ISBN 978-88-548-2030-2, pp. 151e154.

Binda, L., Saisia, A., Tiraboschi, C., Valle, S., Colla, C., Forde, M., 2003. Application ofsonic and radar tests on the piers and walls of the Cathedral of Noto. Con-struction and Building Materials 17 (8), 613e627.

Binda, L., Zanzi, L., Lualdi, M., Condoleo, P., 2004. The use of georadar to assessdamage to a masonry Bell Tower in Cremona Italy. NDT&E International Journal38, 171e179.

Boke, H., Cizer, O., Ipekoglu, B., Ugurlu, E., Serifaki, K., Toprak, G., 2008. Character-istics of lime produced from limestone containing diatoms. Construction andBuilding Materials 22 (5), 866e874.

Docherty, P., 1991. A brief comparison of some Kirchhoff integral formulas formigration and inversion. Geophysics 56 (8), 1164e1169.

Du, S., Rummel, P., 1994. Reconnaissance studies of moisture in the subsurface withGPR. In: Proceedings of the 5th International Conference on Ground PenetratingRadar, pp. 1224e1248.

Endrea, A.L., Knight, R., 1992. A theoretical treatment of the effect of microscopicfluid distribution on the dielectric properties of partially saturated rocks.Geophysical Prospecting 40, 307e324.

Fruhwirth, R.K., Schmoller, R., Oberaigner, E.R., 1996. Some aspects of the estimationof electromagnetic wave velocities. In: Proceedings of the 6th InternationalConference on Ground Penetrating Radar. Tohoku University, Sendai, Japan,pp. 135e138.

Grasso, F., Leucci, G., Masini, N., Persico, R., 2011. GPR prospecting in Renaissanceand baroque monuments in Lecce (Southern Italy). In: Proc. of VI InternationalWorkshop on Advanced Ground Penetrating Radar IWAGPR, Aachen, Germany,June 22e24.

Grandjean, G., Gourry, J.C., Bitri, A., 2000. Evaluation of GPR techniques for civil-engineering applications: study on a test site. Journal of Applied Geophysics45, 141e156.

Greaves, R.J., Lesmes, D.P., Lee, J.M., Toksöz, N., 1996. Velocity variations and watercontent estimated from multi-offset, ground-penetrating radar. Geophysics 61,683e695.

Kadioglu, S., Kadioglu, Y.K., 2010. Picturing internal fractures of historical statuesusing ground penetrating radar method. Advances in Geosciences 24, 23e34.

Leucci, G., Negri, S., Carrozzo, M.T., Nuzzo, L., 2002. Use of ground penetrating radarto map subsurface moisture variations in an urban area. Journal of Environ-mental and Engineering Geophysics 7 (2), 69e77.

Leucci, G., Persico, R., Soldovieri, F., 2007. Detection of fractures from GPR data: thecase history of the Cathedral of Otranto. Journal of Geophysics and Engineering4, 452e461.

Leucci, G., Masini, N., Persico, R., Quarta, G., Dolce, C., 2012a. A multidisciplinaryanalysis of the crypt of the Holy Spirit in Monopoli (Southern Italy). NearSurface Geophysics 10, 1e8.

Leucci, G., Masini, N., Persico, R., 2012b. Timeefrequency analysis of GPR data toinvestigate the damage of monumental buildings. Journal of Geophysics andEngineering 9, S81eS91.

Leucci, G., Masini, N., Persico, R., Soldovieri, F., 2011. GPR and sonic tomography forstructural restoration: the case of the Cathedral of Tricarico. Journal ofGeophysics and Engineering 8, 76e92.

Masini, N., Persico, R., Rizzo, E., Calia, A., Giannotta, M.T., Quarta, G., Pagliuca, A.,2010. Integrated techniques for analysis and monitoring of historical monu-ments: the case of S. Giovanni al Sepolcro in Brindisi (Southern Italy). NearSurface Geophysics 8, 423e432.

Mellet, J.S., 1995. Ground penetrating radar applications in engineering, environ-mental management, and geology. Journal of Applied Geophysics 33, 157e166.

Nuzzo, L., Quarta, T., 2010. A review of geometric issues in GPR prospecting of cy-lindrical structures in cultural heritage applications. In: Proc. of XIII Interna-tional Conference on Ground Penetrating Radar, Lecce, Italy, June 21e25. IEEE.http://dx.doi.org/10.1109/ICGPR.2010.5550198.

Persico, R., Bernini, R., Soldovieri, F., 2005. On the configuration of the measure-ments in inverse scattering from buried objects under the distorted Bornapproximation. IEEE Transactions on Antennas and Propagation 53 (6), 1875e1886.

Pieraccini, M., Luzi, G., Noferini, L., Mecatti, D., Atzeni, C., 2004. Joint time frequencyanalysis of layered masonry structures using penetrating radar. IEEE Trans-actions on Geoscience and Remote Sensing 42 (2), 309e317.

Ranalli, D., Scozzafava, M., Tallini, M., 2004. Ground penetrating radar investigationsfor restoration of historical building: the case study of Collemaggio Basilicata(L’aquila, Italy). Journal of Cultural Heritage 5, 91e99.

Sandmeier, K.J., 2012. Reflexw 6.0 Manual Sandmeier Software ZipserStrabe1 D-76227 Karlsruhe Germany.

Standard NorMaL 12/83, 1983. Aggregati artificiali di clasti e matrice legante nonargillosa: schema di descrizione. C.N.R e I.C.R., Rome.

Standard NorMaL 15/84, 1984. Manufatti e aggregati a matrice argillosa: schema didescrizione. C.N.R e I.C.R., Rome.

Standard UNI 11087/2003, 2003. Beni culturali, Materiali lapidei naturali ed artifi-ciali, Determinazione del contenuto di sali solubili. UNI, Milan.

Stolt, R.H., 1978. Migration by Fourier transform. Geophysics 43, 23e48.Topp, G., Davis, J., Annan, A.P., 1980. Electromagnetic determination of soil water

content: measurements in coaxial transmission lines. Water ResourcesResearch 16, 574e582.

Utsi, E., 2010. The shrine of Edward the confessor: a study in multi-frequency GPRinvestigation. In: Proc. of XIII International Conference on Ground PenetratingRadar, Lecce, Italy, June 21e25. IEEE, ISBN 978-1-4244-4605-6.