Integrated prospecting in the crypt of the Basilica of Saint Nicholas in Bari, Italy

This article has been downloaded from IOPscience. Please scroll down to see the full text article.

2012 J. Geophys. Eng. 9 271

(http://iopscience.iop.org/1742-2140/9/3/271)

Download details:

IP Address: 150.145.56.22

The article was downloaded on 13/04/2012 at 08:45

Please note that terms and conditions apply.

View the table of contents for this issue, or go to the journal homepage for more

Home Search Collections Journals About Contact us My IOPscience

IOP PUBLISHING JOURNAL OF GEOPHYSICS AND ENGINEERING

J. Geophys. Eng. 9 (2012) 271–281 doi:10.1088/1742-2132/9/3/271

Integrated prospecting in the crypt of theBasilica of Saint Nicholas in Bari, ItalyAngela Calia, Giovanni Leucci, Nicola Masini, Loredana Matera,Raffaele Persico and Maria Sileo

Institute for Archaeological and Monumental Heritage IBAM-CNR

E-mail: g.leucci@ibam.cnr.it

Received 9 December 2011Accepted for publication 14 March 2012Published 12 April 2012Online at stacks.iop.org/JGE/9/271

AbstractIn this paper, we present the results of non-destructive integrated geophysical surveys (groundpenetrating radar (GPR) and seismic sonic) performed in the crypt of the Basilica of StNicholas in Bari, Italy. The aim was twofold, namely to investigate the consistency ofrestoration work performed in 1950 and the presence of features of archaeological interest.The GPR technique has also been exploited to characterize the subsurface water content underthe crypt. In particular, the existence of buried anomalies, probably due to the restorationwork, has been identified. Moreover, by means of an electromagnetic-wave velocity analysis,an estimation of the volumetric water content under the floor has been achieved. The resultsindicate the main causes of the deterioration and have provided significant information for thesafeguard of this historical building. Furthermore, the GPR survey allowed us to identify someanomalies buried under the crypt that are probably of archaeological interest. Finally, bothsonic tomography and a GPR survey have been performed on an important mosaic, and haveenabled us to identify probable ‘internal’ reasons for its decay.

Keywords: GPR, amplitude tomography, seismic attenuation tomography, crypt of Basilica ofSt Nicholas in Bari

(Some figures may appear in colour only in the online journal)

1. Introduction

Geophysical investigation in monumental buildings is animportant issue because it is able to provide both historicaland structural information about the monument at hand (Bindaet al 2003, 2004, Ranalli et al 2004, Pieraccini et al 2004,Bavusi et al 2008, Barone et al 2010, Kadioglu and Kadioglu2010, Utsi 2010, Leucci et al 2010). In particular, someissues of structural interest are the possible presence offractures, voids, infiltrations of humidity or metallic barsdue to previous restoration works, possibly dating back tocenturies ago (Sambuelli et al 2010) and not adequatelydocumented. These investigations are well advised especiallyif new restoration works are scheduled. In particular, thenon-destructive investigations can provide information foraddressing the restorations properly and allow one to check thesuccess of the restoration works by means of post-interventionmonitoring. Some issues of historical interest are the presence

of tombs, walled rooms, and hidden pictures, mosaic and floors(Grasso et al 2011, Pieraccini et al 2006). In particular, thechanges that a building has undergone through the centurieshave not been documented in many cases, or in other cases thedocuments have been lost. In some cases, the significance ofa retrieved buried target can be both historical and structural,as for example in the case of a hidden crypt under a church.

With regard to the present case history, theSuperintendence for the Architectonic and the LandscapeHeritage for the Province of Bari and Foggia put the Institutefor Archaeological and Monumental Heritage IBAM-CNR(www.ibam.cnr.it) in charge of a non-invasive geophysicalinvestigation and a geological (petrographic) investigation ofseveral parts of the Basilica of St Nicholas in Bari (ApuliaRegion, Italy). The Basilica is an important monument, aswe will describe in the following, and restoration work isscheduled for it.

1742-2132/12/030271+11$33.00 © 2012 Sinopec Geophysical Research Institute Printed in the UK 271

A Calia et al

Figure 1. Bari: location of the crypt of the Basilica of St Nicholas.

IBAM-CNR has performed a non-invasive investigationin the crypt underlying the church (which contains the relicsof St Nicholas and an artistically important mosaic) and anarea external to the church. The main problem was to gainsome insight into the condition of the church, affected byinfiltrations of humidity and by the presence of buried cavitiesthat might undermine the stability of the building. In this paper,we will focus on the ground penetrating radar (GPR) andseismic prospecting performed in the crypt, which is the mostimportant part of the work.

The paper is organized as follows. In the next sectiona brief historical outlook of the monument is provided. Insection 3, the results of the prospecting on the floor of thecrypt are shown. In section 4, the results of the prospectingon a floor mosaic in the right-hand corner of the crypt arepresented. In section 5, a moisture map is given. Conclusionsfollow in section 6.

2. The Basilica of St Nicholas

The Basilica of St Nicholas is located in the town of Bari,Italy, on the Adriatic Sea (see figure 1), and was not originallya church. In particular, around the year 1000, when a large partof southern Italy was included in the Byzantine Empire, theBasilica was the residence of the Byzantine governor, whichmade Bari an important town from a political and economicalpoint of view. However, in 1071 the Normans conquered thisarea, and a series of political events subsequent to this conquesteventually made Bari quite marginal and peripheral in relationto the role it used to have during the Byzantine period. To giveback to Bari at least part of its ancient renown, in 1087, thetheft of the relics of St Nicholas, held in Myra, a town on thesea in Southern Turkey, was organized. At that time, to have

the relics of a venerated Saint had political and economicalimportance due to the pilgrimages that the relics used toattract. The theft was successful, and so the old building ofthe Basilica was partially demolished and rebuilt, and wasconsecrated as a church in order to hedge in the relics ofSt Nicholas.

The Basilica is a complex and ‘sombre’ Romanesque-style monument, partially decorated by re-employingprecedent Byzantine materials, with several modifications andfurther re-decorations made later through the centuries. For adetailed description of the architecture of the church, we referthe interested reader to the official website of the Basilica,http://www.basilicasannicola.it/. Here, it is important to notethat, beyond having an important historical and artistic value,the Basilica is still the destination for many pilgrims, becauseSt Nicholas is venerated both by Catholic Christians in westernEurope and Orthodox Christians in eastern Europe (let us notethat the schism between the two Churches occurred in 1057,seven centuries after the death of the Saint). Nowadays, bothCatholic and Orthodox masses are celebrated in the crypt of theBasilica. This makes this Basilica a very important monumentbecause it is a place with a meaningful symbolic value forthe modern ecumenical reconciliation process started by theSecond Vatican Council (1962–1965) and still going on withinthe Christian religion.

3. Geophysical investigation on the floor of the crypt

The GPR surveys on the floor of the crypt were performedwith a Ris Hi-Mod system, manufactured by Ingegneria deiSistemi (IDS), equipped with several antennas. In particular,on the floor we have used a double pair of antennas, containedin the same box, with nominal central frequencies of 200

272

Integrated prospecting in the crypt of the Basilica of Saint Nicholas

Figure 2. Location of radar profiles in the crypt of the Basilica.

and 600 MHz, respectively. Data along 69 B-scans gatheredaccording to the scheme were given in figure 2. The distancebetween the scan lines was 0.4 m.

The data were processed by means of zero timing,background removal (the averaging was been performedconsidering all the traces of the current B-scan), gainvariable versus the depth and Kirchoff migration. From theshape of the diffraction hyperbolas, we have evaluated anaverage electromagnetic (EM)-wave velocity equal to about0.07 m ns−1. This gives a relative permittivity εr ≈ 18, workedout from the well-known relationship εr = ( co

c

)2, co being the

velocity of the EM waves in free space and c the undergroundpropagation velocity. We recorded a penetration of the signalradiated with the antenna at 600 MHz of the order of 60 ns,corresponding to a depth of 2.1 m. This can be appreciatedin figures 3 and 4. In particular, figure 3 shows one of theradar sections parallel to the x-axis (oriented roughly east–west) evidenced by a red line in figure 2, and figure 4 showsone of the radar section parallel to the y-axis (oriented roughlynorth–south) also shown by a red line in figure 2.

From figure 3(c), we note the presence of severalreflections in the belt 20–30 ns (corresponding to the depthrange 0.7–1.05 m). These are probably due to a layer ofdifferent material. Below this layer, within the time range 30–45 ns (about 1.05–1.57 m), we see instead some quite precisearch structures (shown by the rectangle in dashed yellow lines),probably due to man-made structures and possibly related toan earlier hypogeum room. Figure 4 shows similar features,just with a small difference in the return times.

One way to obtain useful maps for understanding theplan distribution of reflection amplitudes within specific timeintervals is the creation of horizontal time slices (Goodman

et al 1994, Piro et al 2001). This data representation playsan important role in GPR investigations as it allows an easiercorrelation of the most important anomalies found in the areaat the same return time, thus facilitating the interpretation.As underlined by several authors (for example Conyers andGoodman (1997)) the data sets for time slices should ideallybe derived from a closely spaced parallel profile. Theoretically,the transect spacing should be of the order of one-fourth of thesubsurface wavelength (Hansen and Johansen 2000). In thecase at hand, however, since the nominal central frequency is600 MHz and the relative permittivity has been estimated equalto 18, an interline spacing of the order of 3 cm would have beenrequired. This was not practicable, due to the available time andbudget. However, it should also be said that the unavoidableloss of resolution versus depth in GPR prospecting makes alsoless severe the requirements for the interline space when theinvestigated targets are not shallow. In particular, the Fresnelzone is sometimes approximated as (Conyers 2004)

Fz = 2

√(d + λ

4

)2

− d2 (1)

and provides a widely exploited approximation of thenecessary interline spacing. In equation (1), d is the depthof the target and λ is the underground wavelength. There arealso relationships that account for the limited view angle underwhich the target is illuminated (Persico and Soldovieri 2010),but for a qualitative evaluation, equation (1) is enough. Inparticular, the targets of interest in the cases at hand, as shown,begin at a depth of about 70 cm, which when substituted intoequation (1) gives an interline of the order of 41 cm. Therefore,in the end, the interline space adopted is reasonably adequatefor our purposes. Finally, it is also worth ‘quoting’ that in

273

A Calia et al

(a) (b) (c )

Figure 3. Radar section related to the ‘short’ W–E-oriented profile: (a) raw; (b) un-migrated; (c) migrated.

Figure 4. Migrated radar section related to the N–S-oriented profile.

some cases it is possible to obtain useful images from timeslices constructed even with relatively widely spaced profiles(Goodman et al 1994). Of course, in this case the size ofthe buried targets plays a key role. The time slice maps havebeen built averaging the square amplitude of the radar signalwithin consecutive time windows of width �t. Typically �tis chosen of the order of the dominant period, but differentwidths can be used in order to enhance particular features. Incommon practice, non-overlapping time windows are chosen,although sliding windows could be used instead. In this workthe time slice technique has been used to display the squareamplitude variations within consecutive time windows with�t = 10 ns. The chosen �t corresponds to a layer about0.35 m thick. The time slices have been calculated from 0 to2.4 m. In figure 5, the most interesting among them are shown.

In particular, the anomalies evidenced in figure 5 arealigned in the same way as some archaeological features foundby direct excavation outside the crypt. Therefore, we interpretthese anomalies as being due to the presence of structures ofarchaeological interest.

Due to the presence of groundwater and seawater at abouta depth of 4 m, the data acquired with the 200 MHz antenna donot allow us to investigate deeper levels than those acquiredwith the antenna at 600 MHz, and so are not presented.

4. Integrated prospecting on the right-hand floormosaic

In the crypt is an ancient mosaic, whose location is givenin figure 6. We have performed integrated GPR and seismicprospecting on it.

274

Integrated prospecting in the crypt of the Basilica of Saint Nicholas

Figure 5. Depth slice (0.70–1.05 m): the high amplitude anomalies (dashed black lines) are probably related to structures of archaeologicalinterest.

Figure 6. The mosaic present on the right-hand side of the crypt.

4.1. GPR survey: data analysis and processing

The GPR survey was performed with the same systememployed for the floor, this time with antennas at a nominalcentre frequency of 2 GHz. We gathered 20 B-scans, withtransect spacing of 10 cm (figure 7(a)). Again, it is larger thana quarter of the estimated underground wavelength. However,we were looking for possible causes of decay (linked, forexample, to moisture gradients or to small undergroundfractures). So, we could tolerate some loss of detail. Theprocessing of the data was the same as that performed forthe floor, but of course the parameters retrieved from the dataare different. In particular, we worked out an average EM-wave velocity equal to 0.07 m ns−1, and the signal penetratedreliably up to 10 ns (which means about 0.35 m).

In figure 8, the images relative to the B-scans R2–R5(according to the labels in figure 7(a)) are shown.

From figure 8, we note a first layer about 2 ns deep(corresponding to 0.07 m). This corresponds to a layer underthe tiles of the mosaic. Moreover, a discontinuity in the mediumis visible in the two-way time range of 4–6 ns (0.14–0.21 m).This seems to be related to man-made work: probably to theinitial preparation or to some restoration of the mosaic.

Moreover, several anomalies are visible in the two-waytime range of 1–4 ns (0.035–0.14 m in depth). Due to theirshape and size (about 0.1 m), they are probably related tosmall inhomogeneities such as voids.

Time slices with adjacent time windows with �t = 1 nshave also been calculated.

275

A Calia et al

(a) (b)

Figure 7. (a) The mosaic and the lines of the GPR profiles; (b) the scheme for the seismic refraction.

Figure 8. Mosaic: processed radar sections related to the profiles R2, R3, R4 and R5.

The selected two-way time interval corresponds to a layerapproximately 0.035 m thick, and the time slices are locatedbetween 0 and 0.35 m in depth. The slices shown in figure 9were obtained using the processed data.

The most evident anomalies are in the two-way time rangeof 1–3 ns (0.035–0.105 m in depth). In this range, the highamplitude anomalies (H) have an irregular shape and could be

related to small inhomogeneities. The deeper slices appear tobe more homogeneous.

4.2. Seismic refraction tomography survey: data analysis andprocessing

Seismic tomography was carried out by exciting a seismicenergy source at several locations along the entire perimeter

276

Integrated prospecting in the crypt of the Basilica of Saint Nicholas

Figure 9. Mosaic: depth slices.

of the mosaic, and gathering the propagated energy at receiversdisplaced along a central line according to figure 7(b).Considering the size of the mosaic and its fragility, we chosethis measurement configuration in order to avoid shots onthe tesserae. On the other hand, similar layouts had alreadybeen exploited in the past (Luzio et al 1987) allowing us toobtain meaningful information about the internal structure ofthe mosaic.

A total of 21 receivers were installed along a single line,with intervals of 0.1 m. Sources were located at 80 locationswith intervals of 0.1 m. A total of 2000 records were made(also considering double shots), of which 1680 were selectedfor further processing after heuristic quality control. Thesource was a triggered hammer (1 kg weight), while verticalgeophones with a resonance frequency of 55 kHz were usedas receivers. Data were recorded on a multi-channel TDASseismograph produced by Boviar s.r.l. The acquisition param-eters were (i) a sample interval of 1 μs and (ii) a time recorderwindow of 10 ms. In figure 10, the waveform of the commonsource data gathered from the first shot location is shown.

Following quality control and some processing of the fieldrecords, only the first arrivals were used in the tomographicanalysis. The error in time picking was calculated to be ofthe order of 0.05 ms. A time–distance plot for some of thetotal first arrivals is presented in figure 11. From figure 11, itcan be seen that the mean arrival time is of the order of 0.9ms. An average velocity of 950 m s–1 was calculated from thetomographic data.

With reference to a dominant transmission frequency ofabout 3 kHz, this yields an average wavelength of about 0.32 m.

Figure 10. The record from the shot labelled ‘1’ in figure 7(b). Thered crosses pick the first arrival times.

Under these conditions, the average vertical and horizontalresolution are estimated to be of the order of 0.08 and 0.29 m,respectively.

The inversion of the travel time data was preformed usinga simultaneous iterative reconstruction technique algorithm

277

A Calia et al

Figure 11. Dromocrones relative to some of the shot points.

Figure 12. The amplitude spectrum related to the records shown in figure 10.

(Hayashi and Takahashi 2001, Morey and Schuster 1999,Parasnis 1997), making use of the ReflexW software(Sandmeier 2011). This involves modification of an arbitraryinitial velocity model by repeated cycles of three steps:(i) forward computation of model first arrival travel times;(ii) calculation of travel time residual; (iii) application ofvelocity corrections.

The starting velocity model consisted of a single layerwith a uniform velocity of 950 m s–1. Minimum and maximumallowable velocities with values of 200 and 2000 m s−1,respectively, were applied as global constraints in the inversionprocedure, in order to incorporate a priori information in thecalculation. The inversion process converged after ten curvedray iterations, with a RMS value of 0.1 ms, which representsa mean error of about 11% with respect to the mean measuredtravel time (0.9 ms).

For amplitude inversion, the no-scattering assumptionwas employed. This means that all the amplitude variationswere interpreted as absorption effects once the data hadbeen reduced for the geometrical spreading. For theamplitude tomography all seismograms were analysed andtrace-spectrum filtering was performed. This allowed thecalculation of the amplitude spectrum of each trace for anyacquired seismogram (figure 12). The reference amplitudewas chosen equal to the amplitude of the wavelet receivedin correspondence with the shortest source–receiver distance,statistically averaged between all the shortest distance signals.

To process the data, a square grid, 0.1 × 0.1 m2, wasdesigned. Also, for the amplitude tomography, the startingattenuation rate model was a single layer with a uniformattenuation rate of 0.5 m dB–1. Horizontal tomograms ofvelocity and attenuation rate are shown in figure 13.

278

Integrated prospecting in the crypt of the Basilica of Saint Nicholas

Figure 13. Tomograms of the results from the inversion of experimental data: (a) velocity; (b) attenuation rate.

For the velocity tomogram of figure 13(a), three differentranges of velocities were found: (i) high velocity anomalies,labelled H (velocities ranging from 1100 to 1800 m s−1);(ii) low velocity anomalies, labelled L (velocities ranging from200 to 600 m s−1); (iii) medium velocity anomalies, labelledM (velocities ranging from 700 to 1000 m s−1).

With regard to the attenuation rate, the results offigure 13(b) show higher (H) values (ranging from 0.7 to1 m dB–1), probably resulting from the presence of cohesivematerial, medium values (M, ranging from 0.05 to 0.5 m dB–1),related to the probable presence of degraded material and/orempty spaces, and low (L, under 0.05 m dB–1) values.

The comparison of the results of the sonic (figure 9) andthe GPR slices (figure 13) makes us think of the presence ofsmall voids in the lower part of the mosaic. In fact the mostmeaningful GPR anomalies in the depth range of 3.5–10 cmroughly correspond to the lowest seismic velocities, in thelower left-handed corner of figures 9 and 13(a).

5. Analysis of the velocity of the EM waves andmoisture map

The EM-wave velocity plays an important role in definingshallow subsurface water content. Several studies have madeuse of GPR techniques to determine subsurface moisture(Annan et al 1990, Du and Rummel 1994, Mellet 1995,Grandjean et al 2000, Leucci et al 2002). However, often thetechniques are considered in specific contexts and quite rarelyare they compared with each other for a parity of externalconditions. In particular, for most dry geological materials,the relative dielectric permittivity, εr, varies between 4 and10. However, if even a small amount of water is containedin the material, the value of the relative permittivity εr canincrease considerably and, conversely, the EM-wave velocitywill decrease significantly. Thus εr can be an index for themeasure of the water content of the ground. Several formulaehave been developed, both theoretical and empirical, to providethe dielectric response of heterogeneous mixtures such as (but

not only) water-saturated soils. One of them is the complexrefractive index method (CRIM) equation, which is often usedin the interpretation of EM logging data (Greaves et al 1996).As affirmed by several authors (Greaves et al 1996, Endrea andKnight 1992), the major problem with the CRIM formula isthat it does not take into account geometrical information aboutthe internal structure of the rocks and about the microscopicfluid distribution. This has a significant effect on the dielectricproperties of partially saturated rocks (Endrea and Knight1992). This restriction may be overcome by using the Hanai–Bruggeman formula (Endrea and Knight 1992). However, themain problem with the two previous approaches is that it is notpossible to derive both the porosity and the water content fromthe dielectric constant. Therefore, it is not possible to obtaininformation about the water content without strong a prioriassumptions. For this reason, we prefer to use the well-knownempirical equation derived by Topp et al (1980), relating thesub-superficial relative dielectric permittivity to the net watercontent w.

This formula is given by

w = −5.3 × 10−2 + 2.9 × 10−2εr − 5.5

× 10−4ε2r + 4.3 × 10−6ε3

r . (2)

This equation was found to be nearly independent of thesubsurface texture, bulk density, temperature and salinity(Du and Rummel 1994). With regard to the measurementconfiguration, the EM-wave velocity can be estimated fromGPR data in several ways (Conyers and Goodman 1997,Huisman et al 2003); the conventional methods involvecommon depth-point and wide-angle reflection and refractiondata sets. Both methods require two separable antennas andrelatively long acquisition times. The EM-wave velocity canbe more quickly and easily determined from the reflectionprofiles acquired in continuous mode, using the shape of thediffraction hyperbolas (Fruhwirth and Schmoller 1996). In thedata set at hand, several hyperbolic reflections caused by smallobjects are present, enabling us to perform a wave velocityanalysis.

279

A Calia et al

Figure 14. Volumetric water-content (w) as a depth slice using0.70–1.05 m depth windows.

Let us say that we have examined both the migratedand un-migrated section, and on the basis of this we haveretained for the velocity analysis only the hyperbolas thatwe have deemed as being related to small targets. Theapplication of this method provided vertical and lateralvelocity values ranging within an uncertainty belt of 0.065 to0.090 m ns−1, respectively. In particular, an average velocity of0.077 m ns−1 was obtained over the survey area. By applyingthe empirical Topp formula (equation (2)), we then obtained anestimate of the average volumetric underground water contentdown to the depth of the point-source reflector, varying fromabout 20% to 36% and increasing with the depth.

Figure 14 shows the plan distribution of the volumetricwater content on the surveyed area. In this figure, thevolumetric water content is also displayed as a depth slicein the window 0.7–1.05 m. The yellow area, which representslower velocities, corresponds to a higher water content (about22–28%). The blue region in the rest of the figure correspondsinstead to the higher velocities, and thus to the lowest watercontent (about 10–15%). The higher values of humidity areprobably related to water infiltration from the surface externalto the crypt. According to figure 14, two areas with highmoisture content seem to be located within the areas delimitedby dashed closed curves. These areas correspond to twozones restored in 1950, so we hypothesize possible ways forpenetration of humidity in these zones, as shown by the arrows.

6. Conclusions

In this paper, we have shown the results of integratedprospecting in the crypt of the Basilica of St Nicholas in Bari(Apulia, Italy). The GPR methodology allows us to locateburied archaeological remains and to estimate the level ofmoisture around them, whereas seismic data can be relatedmore quantitatively to specific hypotheses about the causes ofthe degradation.

The existence in the radar sections of many hyperbolicanomalies, due to small inhomogeneities, made it possible to

perform an EM-wave velocity analysis. This, in turn, made itpossible to estimate water content variations underground.

We observed a significant increase in values of humiditythat are probably related to water infiltration from the surfaceexternal to the crypt, and a significant rise of water from thefloor near a zone restored in 1950.

Moreover integration between high resolution GPR andseismic refraction tomography measurements allowed us tounderstand the conservation condition of an important mosaic.In particular, data analysis makes us suspect the presence ofsmall voids in the lower part of the mosaic.

The ability of GPR to provide information about thestructure of a mosaic and about its preservation state has alsobeen studied in other cases, and also test mosaics have beenset up to estimate the performance achievable (Derobert et al2004). To the best of our knowledge there is still no universallyaccepted protocol for this. However, general rules of thumbare certainly the use high-frequency antennas, surely beyondthe GHz, closely spaced lines (if possible, one fourth of theestimated sub-superficial wavelength, though this can be anunpractical value and so the choice is also driven by the kindof anomalies looked for) and a particular carefulness aboutthe positions of the data, especially for large mosaics (tens ofsquare metres) and narrow transects (less than 10 cm). If somespecific hypothesis for the interpretation of the buried targetsis probable, then forward modelling can be useful, as done forexample in Utsi (2006). However, this was not the case forthis investigation, where the GPR results were compared withseismic prospecting results in order to test the likelihood of theinterpretation about the most damaged area. In particular, forour mosaic, from the comparison between GPR and seismicresults, we have estimated the most probable causes of decayas due to underlying small voids or cracks.

References

Annan P A, Cosway W S and Redman J D 1991 Water tabledetection with ground penetrating radar Soc. ExplorationGeophysicists Ann. Meeting, Houston, TX, USA ExpandedAbstracts pp 494–6

Barone P M, Lauro S E, Mattei E and Pettinelli E 2010Non-destructive technique to investigate an archaeologicalstructure: a GPR survey in the Domus Aurea (Rome, Italy)IEEE Proc. 13th Int. Conf. on Ground Penetrating Radar(Lecce, 21–25 June) pp 250–4 ISBN 978-1-4244-4605-6

Bavusi M, Piscitelli S, Soldovieri F, Crocco L, Prisco Gand Vallianatos F 2008 Exploitation of a microwavetomographic approach for GPR data processing collected athistorical buildings of Chania (Crete, Greece) Advances inRemote Sensing for Archaeology and Cultural HeritageManagement ed R Lasaponara and N Masini (Rome: Aracne)pp 151–4, ISBN: 978-88-548-2030-2

Binda L, Saisia A, Tiraboschi C, Valle S, Colla C and Forde M 2003Application of sonic and radar tests on the piers and walls ofthe Cathedral of Noto Constr. Build. Mater. 17 613–27

Binda L, Zanzi L, Lualdi M and Condoleo P 2004 The use ofgeoradar to assess damage to a masonry bell tower in Cremona,Italy NDT&E Int. J. 38 171–9

Conyers L B 2004 Ground-Penetrating Radar for Archaeology(Walnut Creek, CA: Alta Mira)

Conyers L B and Goodman D 1997 Ground-Penetrating Radar: AnIntroduction for Archaeologist (Walnut Greek, CA: Alta Mira)

280

Integrated prospecting in the crypt of the Basilica of Saint Nicholas

Derobert X, Cote P, Miltiadiou-Fezans A and Delinikolas N 2004Expected performances for mosaic-grouting monitoring byGPR Proc. 10th Int. Conf. on Ground Penetrating Radar (Delft,the Netherlands, 21–24 June) pp 147–50

Du S and Rummel P 1994 Reconnaissance studies of moisture in thesubsurface with GPR Proc. 5th Int. Conf. on GroundPenetrating Radar pp 1224–48

Endrea A L and Knight R 1992 A theoretical treatment of the effectof microscopic fluid distribution on the dielectric properties ofpartially saturated rocks Geophys. Prospect. 40 307–24

Fruhwirth R K and Schmoller R 1996 Some aspects on theestimation of electromagnetic wave velocities Proc. 6th Int.Conf. on Ground Penetrating Radar (GPR’96) (Sendai, Japan,30 September–3 October) pp 135–8

Goodman D, Nishimura Y and Tobita K 1994 GPRSIM forwardmodeling software and time slices in ground penetrating radarsurveys Proc. 5th Int. Conf. on Ground Penetrating Radar(GPR’94) (Kitchener, Ontario, Canada, 12–16 June) pp 31–43

Grandjean G, Gourry J C and Bitri A 2000 Evaluation of GPRtechniques for civil-engineering applications: study on a testsite J. Appl. Geophys. 45 141–56

Grasso F, Leucci G, Masini N and Persico R 2011 GPR prospectingin Renaissance and Baroque monuments in Lecce (SouthernItaly) Proc. 6th Int. Workshop on Advanced GroundPenetrating Radar IWAGPR (Aachen, Germany, June) pp 22–4

Greaves R J, Lesmes D P, Lee J M and Toksoz N 1996 Velocityvariations and water content estimated from multi-offset,ground-penetrating radar Geophysics 61 683–95

Hansen T B and Johansen P M 2000 Inversion scheme for groundpenetrating radar that takes into account the planar air–soilinterface IEEE Trans. Geosci. Remote Sens. 38 496–506

Hayashi K and Takahashi T 2001 High resolution seismic refractionmethod using surface and borehole data for site characterizationof rocks Int. J. Rock Mech. Min. Sci. 38 807–13

Huisman J, Hubbard S, Redman J and Annan A 2003 Measuringsoil water content with ground penetrating radar: a reviewVadose Zone J. 2 476–91

Kadioglu S and Kadioglu Y K 2010 Picturing internal fractures ofhistorical statues using ground penetrating radar method Adv.Geosci. 24 23–34

Leucci G, Masini N, Persico R, Quarta G and Dolce C 2012 Amultidisciplinary analysis of the Crypt of the Holy Spirit inMonopoli (Southern Italy) Near Surf. Geophys. 10 57

Leucci G, Negri S, Carrozzo M T and Nuzzo L 2002 Use of groundpenetrating radar to map subsurface moisture variations in anurban area J. Environ. Eng. Geophys. 7 69–77

Luzio D, Margiotta C and Ranieri G 1987 Analisi comparata dimisure geoelettriche e sismiche per l’individuazione di cavitanell’area archelogica di Roca (Lecce) Atti del Convegno sulleConoscenze Geologiche del Territorio Salentino (Lecce,12 December 1987) pp 355–72

Mellet J S 1995 Ground penetrating radar applications inengineering, environmental management, and geologyJ. Appl. Geophys. 33 157–66

Morey D and Schuster G T 1999 Paleoseismicity of the OquirrhFault, Utah from shallow seismic tomography Geophys. J. Int.138 25–35

Parasnis D S 1997 Principles of Applied Geophysics 5th edn(London: Chapman and Hall)

Persico R and Soldovieri F 2010 Recent issues relevant to GPRprospecting Proc. EMTS (Berlin, Germany) pp 88–92

Pieraccini M, Luzi G, Noferini L, Mecatti D and Atzeni C 2004 Jointtime frequency analysis of layered masonry structures usingpenetrating radar IEEE Trans. Geosci. Remote Sens. 42 309–17

Pieraccini M, Noferini L, Mecatti D, Atzeni C, Persico Rand Soldovieri F 2006 Advanced processing techniques forstep-frequency continuous-wave penetrating radar: the casestudy of ‘Palazzo Vecchio’ walls (Firenze, Italy) Res.Nondestruct. Eval. 17 71–83

Piro S, Goodman D and Nishimura Y 2001 High-resolutionground-penetrating radar survey at Forum Novum—Vescovio:studying urbanism in the Tiber valleyJ. Roman Archaeol. 14 59–79

Ranalli D, Scozzafava M and Tallini M 2004 Ground penetratingradar investigations for restoration of historical building: thecase study of Collemaggio Basilicata (L’Aquila, Italy)J. Cultural Heritage 5 91–9

Sambuelli L, Calzoni C, Stocco S and Rege R 2010 Geophysicalmeasurements on the occasion of the moving of an ancientEgyptian sculpture Proc. GNGTS Conf. (Trieste, Italy, 16–19 November) pp 595–9

Sandmeier K J 2011 ReflexW 6.0 Manual, Sandmeier Software,Zipser Strabe1, D-76227 Karlsruhe, Germany

Topp G, Davis J and Annan A P 1980 Electromagneticdetermination of soil water content: measurements in coaxialtransmission lines Water Resour. Res. 16 574–82

Utsi E 2006 Improving definition: GPR investigation at WestminsterAbbey Proc. 11th Int. Conf. on Ground Penetrating Radar(Columbus, OH (USA), June) pp 19–22

Utsi E 2010 The shrine of Edward the Confessor: a study inmulti-frequency GPR investigation Proc. 13th Int. Conf. onGround Penetrating Radar (Lecce, Italy, June) pp 21–5

281