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Integrated geophysical research of Bourbonic shipwrecks sunk in the Gulf of Naples in 1799

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  Integrated geophysical research of Bourbonic shipwrecks sunkin the Gulf of Naples in 1799 Gaia Mattei ⁎ , Francesco Giordano Dip. di Scienze e Tecnologie, Università Parthenope di Napoli, Napoli, Italy a b s t r a c ta r t i c l e i n f o  Article history: Received 10 September 2014Received in revised form 30 October 2014Accepted 13 November 2014Available online 2 December 2014 Keywords: Geophysical surveyUnderwater archeologyBourbonic shipwrecksGIS In1798,FerdinandIVofBourbon,KingofNaples,lostthebattlewiththeFrenchforcontrolofthePapalStatesandwas obliged to escape from Naples. On January 9, 1799, Admiral Campbell sank the ships that remained in theport due to a lack of crews, by setting them on  󿬁 re on the orders of Admiral Nelson. This action was taken toprevent the remaining ships from falling into the hands of the French, who were about to enter the city.This article describes the results of an integrated geophysical survey undertaken to detect the warships sunk in1799. The initial study area was broadly de 󿬁 ned by reference to a historical map of 1828, which purported toshow the position of the shipwrecks.The geophysical methods employed consisted of the seismic-stratigraphic method (sub-bottom pro 󿬁 ler), themorphologic method (acoustic image — side-scan sonar) and the magnetometric method. The objectives of thesurveys were to accurately locate the shipwrecks and to characterize the seabed sediments and wrecksthemselves in order to understand the process of the sinking of the vessels.Two of the shipwrecks, the St.Gioacchino and the Pallade vessels, were located using these non-invasivemethods, partially buried within soft seabed sediments. Future research of the sites will be undertaken byappropriately quali 󿬁 ed underwater archaeologists who will collect  󿬁 eld data that can build on and verify theresults of these surveys.© 2014 Published by Elsevier Ltd. 1. Introduction InNovember1798,FerdinandIVofBourbon,KingofNaples,orderedtheFrenchtoclearthePapalStateand,withhisArmy,enteredRomeasa liberator. The French, under the command of General Jean ÉtienneChampionnet, won Rome back and moved towards Naples. AdmiralNelson,anallyoftheBourbons,sailinghis 󿬂 agshipVanguard,organizedthe escape of Ferdinand and his family to Sicily. They left on December26, 1798, escorted by part of the Neapolitan  󿬂 eet (Colletta, 1861).Most of the  󿬂 eet, due to the lack of crew members, remained in NaplesunderthecommandofMarquisdeNisa,AdmiralofthePortuguese 󿬂 eetand allyof theEnglish. Hereceived from Nelson the order to sinkthoseshipsthatcouldnotsailincasetheFrenchenteredNaples.OnDecember28, the Frigate Pallade was scuttled by enlarging existing leaks. On Jan-uary 1, 1799, Portuguese Admiral de Nisa left and ordered the EnglishAdmiral Campbell, working for the Portuguese, to set  󿬁 re to the ships.On the night between January 8 and 9, 1799, even though the Frenchwere still far from Naples, orders were given to set  󿬁 re and sink all theremaining vessels:  “ Tancredi, ” “ Guiscardo ”  and  “ St. Gioacchino, ”  thecorvette  “ Flora ”  and the gabarra  “ Lampreda ”  (Radogna, 1978).The purpose of this research is to accurately locate, for the  󿬁 rsttime, the warships sunk in 1799 off the port of Naples and to distin-guish them from other objects, such as naval cannons and hulls,fragments that have accumulated in almost three thousand yearsand now partially covered by mud on the seabed. For this study,we have used geophysical methods (Quinn et al., 2002; Quinn,2006; Arnott et al., 2005). According to Duck (1993), Blake (1995) and Giordano (2010), the side-scan sonar is a powerful system forarchaeological investigation because it can image structures and ar-tifacts elevated from the seabed. Side-scan sonar, sub-bottom pro- 󿬁 ler (Quinn et al., 1997, 2002; Bull et al., 1998), single- and multi-beam echo sounder and magnetometer (Arnold, 1981, 1996;Passaro et al., 2009) are frequently used today for the localizationand characterization of shipwrecks (Breen and Barton, 1998;Quinn et al., 2002; Plets et al., 2008).Until this work, the only documentation of the position of theshipwrecks of the Bourbonic  󿬂 eet in the Port of Naples was an old map(scale 1:5000), dated to 1828 and entitled  “ Plant of the City of Naplesandits surroundings delineated andengraved in the Royal TopographicFactory of War ”  (Carola, 1999).The aims of the integrated seismic-stratigraphic (SBP), morphologic(SSS)andmagnetometric(MAG)surveyshavebeentolocatethepreciseposition of two Bourbonic shipwrecks, approximately located from theancient map, and to characterize, the lithology and morphology of the  Journal of Archaeological Science: Reports 1 (2015) 64 – 72 ⁎  Corresponding author at: Centro Direzionale Isola, C4, 80143 Napoli, Italy. Tel.: +390815476635; fax: +39 3471231700. E-mail address: (G. Mattei).© 2014 Published by Elsevier Ltd. Contents lists available at ScienceDirect  Journal of Archaeological Science: Reports  journal homepage:  seabed study area, in order to understand taphonomic processes associ-ated with the wrecking of the vessels. 2. The study area The positions of the shipwrecks according to the historic map areshown in Fig. 1A. The depth of the sea in the research area is between30 and 40 m (Fig. 1B). Using the results from previous studies (Milia et al., 1998; Sbrana et al., 2007) and through surveys carried out with apowerful sub-bottom pro 󿬁 ler, EG&G Uniboom and Dseismic acquisitionplatform(Corradietal.,2003),theacousticsignalsofthesuper 󿬁 cialfacieswere identi 󿬁 ed in the area around the shipwrecks (Fig. 1C). This facies istypical of thesediment cover and is madeup of  󿬁 nesoft sediments, withlow re 󿬂 ectivity(Fig. 1C). 3. The localized shipwrecks The shipwrecks identi 󿬁 ed in this study are the San Gioacchino andthe Pallade, and their precise position has been corrected with respectto the location recorded on the historic map (Fig. 1A).The vessel San Gioacchino was purchased by the Bourbon Navy inMalta in 1784 (Carola, 1999; Radogna, 1978). It was armed with 64weapons, of which 26 were 24-caliber guns, 28 were 12-caliber gunsand 10 were 6-caliber guns. According to Carola (1999), these guns Fig. 1.( A)Historical chartfortheyear 1828,indicating theapproximatelocationsofthe San Gioacchino and Palladewrecks.(B) Study areachart with the precise position ofshipwreckslocated by geophysical surveys: T12 is Pallade Fregate and T06 is S. Gioacchino Vassel. (C) Seismic interpreted pro 󿬁 le: F1 showing chaotic sediments with low re 󿬂 ectivity; F2 sedimentswith regular strati 󿬁 cation and high re 󿬂 ectivity, are representative of more compact deposits, which are probably of volcanic srcin.65 G. Mattei, F. Giordano / Journal of Archaeological Science: Reports 1 (2015) 64 – 72  werealmostcertainlycarriedtolandbeforethesinking.Theshipwouldhave had the following approximate dimensions: a displacement of 3000 tons, a length of 50 m and width of 14 m, a draft of 7 m, 3 mastsmore bowsprit, square sails. It would have required a crew of about400 men.TheFrigatePalladewas 󿬁 rstlaunchedinCastellammarediStabiaonSeptember 18, 1786. Her dimensions were 45.47 m in length and11.75 m in width. It was armed with 36 weapons (Radogna, 1978). 4. Survey equipment and methodology  The integrated geophysical survey comprised a side-scan sonarsurvey,asub-bottompro 󿬁 lersurveyandanOverhausereffectmagneto-metric survey. Positional information for the shipwrecks surveys wasprovided by a Trimble DSM232 GPS unit for marine applications, withOmnistar corrections (Fig. 2).The surveys in the area identi 󿬁 ed from the historical map werecarried out in three consecutive periods, each dedicated to a speci 󿬁 cgeophysical system. Each survey provided a series of results, whichsuggest the presence of targets compatible with the wrecks. AGISoverlay of all results was used to better identify the precise position of shipwrecks with respect to the historical map (Fig. 3).Themorphologicsurveys(SSS)wereplannedin7west-eastnaviga-tion lines. The GEOACOUSTIC Side-Scan Sonar device (TransceiverModel SS981, Tow 󿬁 sh Model 159D, and Multiplexer — Model SS982,114 – 410 KHz), made of a tow 󿬁 sh with two lateral transducers, a cablefordata transmissionand a control unit for data acquisition and record,was used at the frequency of 410 kHz. The data were processed usingthe Sonarweb software (Chesapeake Technology) producing the Geotif  󿬁 le.Theacousticaltargetscompatiblewiththeshipwreckswereidenti- 󿬁 edbycarefullyinterpretingthesonographsacquiredduringthesurvey.Thesonograph 󿬁 leswereimportedintoaGISasagridlayertodeter-minatetheprecisepositionoftheacousticaltargetsidenti 󿬁 ed.Finally,a3Dmodelproducedbyextrusionprocessingwasusedtoreconstructtheshape of each shipwreck and particularly to highlight their extrudedand buried parts.The sub-bottom pro 󿬁 ler stratigraphic surveys (SBP) were carried outaccording to a west-east navigation line of 4900 m (Fig. 2). The SAM 96Sparker (Corradi et al., 2003) was used as seismic source; it is a multi-electrode acoustic source, with very high-resolution and an acousticimpulse of about 1 ms in time. It is therefore suitable for shallow watersand for archaeological research due to its excellent resolution. It offers10 – 20 cm vertical resolution and shooting energy adaptable to speci 󿬁 cneeds of 100, 200 and 400 J. During the survey, a shooting energy of 200 J was employed. The acoustic response of the super 󿬁 cial layers of alltheseismicpro 󿬁 leswereanalyzedindetailtode 󿬁 netheseabed ’ sgeo-logical characteristics (Fig. 2) and to determinate the targets compatiblewith the presence of a shipwreck, including those partially buried. Thepositions of localized targets were entered in GIS as a point layer.The magnetometric surveys (MAG) were carried out according to awest-eastnavigationlineof3000m(Fig.2).ASeaquestMarineMagneticsystem was used with a sensitivity of 0.01 nT. It is an Overhauser effectmarine magnetometer, a magnetic platform that is designed to detectferrous object and targets in marine environments. The Overhausersensor measures magnetic  󿬂 ux density, the unit for which is theTesla (T). Magnetic Flux density on the surface of the Earth typically Fig. 2. Integratedgeophysicalsurvey navigation map (UTM 33N WGS84co-ordinatesystem).The redcircles indicatetheoff-limit navigation areasduringthemagnetometric survey forthe presence of   󿬁 shing nets.66  G. Mattei, F. Giordano / Journal of Archaeological Science: Reports 1 (2015) 64 – 72  varies between about 18  μ  T to 70  μ  T, depending to location. The  󿬂 uxdensity at any  󿬁 xed location of the Earth ’ s surface also varies withtime due to diurnal effects, which include the in 󿬂 uence of the Sunand the movement of theEarth ’ s molten interior. Magnetic methodsareveryusefulinmarinearchaeologicalstudies(Paolettietal2003).MAG survey results were used to identity individual magnetic anom-aliesproducedbyshipwrecks.ThegeomagneticprospectingmeasurestheEarth's magnetic 󿬁 eld variations, caused by the presence of undergroundelements with anomalous magnetic characteristics. The magnetic datawereimportedintotheGISasageoreferencedpointlayer.Thecalculationofthetotalmagnetic 󿬁 eld(TMF)anomalyincloseproximitytothewreckshas allowed a calculation of the iron mass contained in each wreck. 4.1. Location and positioning methods The location and georeferencing of the ships was performed inArcGIS 10.1 using the UTM (33 N) WGS84 co-ordinate system. Themethodology consisted of the mapping of the spatial position of thedetected targets during the surveys as an overlay. If the three geophys-icaltechniques(oratleasttwo)identi 󿬁 edapointincloseproximitytoawreck identi 󿬁 ed on the historical map, then it is more likely that thispoint is the real position of a shipwreck. The coding methodologyused to evaluate the importance of targets is in Table 1. 4.2. GIS project  All phases of this research were supported by a project GIS project(Mattei, 2010) structured in modules that managed both planning andprocessing of data from the three surveys.Furthermore, spatial analysis of the overlaid geophysical data (SSSGeotif,pointsofSBPacoustictargetsandpointsofmagneticanomalies)has allowed the geographical position of two targets compatible withthe shipwrecks of the Bourbonic  󿬂 eet to be identi 󿬁 ed.In particular, the grey scale image of the SSS mosaic wasgeoreferenced in ArcGIS ArcMap 10.1 and subsequently processedin ArcGIS ArcScene 10.1, allowing the reconstruction of the elevation of the acoustic targets on the basis of backscattering values (grey scale).The3Dmodeling,bymeansofextrusion,wasobtainedapplyingasuitable  Z   scale factor to the grey scale image values, utilizing the  “ elevation fromsurface ”  command. The georeferencing of the SBP acoustic targets hasallowedtheidenti 󿬁 cationoftargetsthatareclosetothewrecksprevious-lyidenti 󿬁 edontheSSSmosaic.Themagnetometricsurveywasanalyzed,evaluating the trend of total magnetic  󿬁 eld in the study area. A detailedanalysis of measured magnetic anomalies relative to the average valueof the local magnetic  󿬁 eld was carried out using the  󿬁 eld calculator inArcMap. The overlay of these results with the SSS mosaic has providedthe trend of total magnetic  󿬁 eld near to the acoustic targets (in Fig. 7)and the calculation of magnetic anomaly values in proximity of thewrecks.In the GIS project, the historical maps were georeferenced, and thecited wreck positions were overlaid and compared with those of thenewly identi 󿬁 ed geophysical targets. Finally, the difference betweenthe two spatial positions of the two were calculated, in meters. 5. Results Aside-scansonarandsub-bottompro 󿬁 leracousticresponsecharac-terized the sea 󿬂 oor of the area, indicating that the shipwrecks arepartially buried by recent, soft  󿬁 ne sediments with chaotic structure,lying on a facies with thin, regular strati 󿬁 cation with high frequencies,probably of volcanic srcin.In the side-scan sonar data,the seabed sed-iments around the shipwrecks are characterized by a low-backscatteracoustic response (Fig. 4A and D). In the sub-bottom pro 󿬁 ler data, thesuper 󿬁 cial facies (F1 in Fig. 1C) is graphically de 󿬁 ned by chaotic markswith little inner re 󿬂 ectivity, low lateral continuity and low frequency.This facies could be a mixture of   󿬁 ne recent sediments with a chaoticstructure,4 – 5mthick(thicknessesarestated,takingintoconsiderationtheconventionalpropagationspeedof1500m/s).TheF2facies(Fig.1C)is de 󿬁 ned by marks with thin and regular strati 󿬁 cation, with highfrequencies, slightlyundulated; itis approximately6m thickandprob-ably composed of unlithi 󿬁 ed but volcanic material. Fig. 3.  Research phases: (1) Historical map of 1828 with approximate shipwreck positions;(2) side-scan sonar survey layer; (3) magnetometric survey layer; (4) sub-bottom pro 󿬁 lesurvey layer; (5) GIS spatial overlay of all captured data, that produced the precise positionof the wrecks.  Table 1 Coding methodology used to identify targets.SBP SSS GM Target unit Target level Target relevance (score) Target position 0  0 0 No target Null Null Null 0  0 1 MG Low 1 Buried 0  1 0 SSS Low 1 Outcropping from the sea 󿬂 oor 0  1 1 SSS and MG INTERM. 2 Outcropping from the sea 󿬂 oor 1  0 0 SBP Low 1 Outcropping from the sea 󿬂 oor or buried 1  0 1 SBP and MG INTERM. 2 Outcropping from the sea 󿬂 oor or buried 1  1 0 SBP and SSS INTERM. 2 Outcropping from the sea 󿬂 oor or buried 1  1 1 SBP, SSS and MG MAX 3 Outcropping from the sea 󿬂 oor or buried67 G. Mattei, F. Giordano / Journal of Archaeological Science: Reports 1 (2015) 64 – 72  The side-scan data clearly imaged the two acoustic targets compati-ble with the shipwrecks. In Fig. 4A, the 󿬁 rst target, compatible with theSt. Gioacchino shipwreck (named T06), is clearly visible as a strong re- 󿬂 ector, orientated E – W. In plan, it extends over an area 50 m × 14 m(Fig. 4A) and is located 200 m (4 cm on the historical map scale) fromtheshipwreckpositionindicatedonthemapof1828.Thetargetislocat-ed at a depth of 40 m and is elevated approximately 0.5 m above theseabed.The second target (Fig. 4D) named T12 was identi 󿬁 ed on asonograph as a strong re 󿬂 ector of the wreck perimeter, orientatedNNW – SSE and a distance of 145 m (2.9 cm on the historical mapscale) from the location of the vessel Pallade on the chart of 1828; itwas located at a depth of 30 m. This spatial coverage of the imagecorresponded with the dimension of the wreck (44 m × 12 m).In Fig. 4b and Fig. 4e, the 3D model (constructed by extrusion pro- cessing) clearly shows the perimeter of the wrecks, reconstructed inFig. 4C and F.TheSt.Gioacchinoisalsoidenti 󿬁 edclearlybythesub-bottompro 󿬁 ledata.InFig.5,itisclearlyvisibleintheareabyaninversionphaseofthesignal that may be caused by the shipwreck (Quinn et al 1998).In Fig. 6, the acoustic response of the wreck is also shown by theanalysis of the signal.Thesignalreceivedbyre 󿬂 ectionfromthewreck,initsinitialpart,has an amplitude of approximately ¼ of those received from the Fig. 4. Targets SSScompatiblewiththeshipwrecks of Bourbonic 󿬂 eet, extractedfrom theSSSsonographs. InpanelsAand D,thebackscattering valuesareinarangescalebetween 0and255, gray scale of the GEOTIF. (A) St. Goacchino vessel T06 target, with spatial dimensions of 50 m × 14 m. (B) The 3D model of the T06 target image with a suitable  Z   scale factor todelineate the target elevation with respect to the seabed. (C) Vector reconstruction of the St. Gioacchino by means of the digitalization of the wreck perimeter visible in the sonograph.(D) Pallade vessel T12 target, with spatial dimension 43 m × 12 m. (E) The 3D model of the T12 target image with a suitable  Z   scale factor to delineate the target elevation with respectto the seabed. (F) Vector reconstruction of the Palade by meansof the digitalization of the wreck perimeter visible in the sonograph.68  G. Mattei, F. Giordano / Journal of Archaeological Science: Reports 1 (2015) 64 – 72
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