Remote Sensing and Archaeological Prospection in Apulia, Italy

Maney Publishing Trustees of Boston University Remote Sensing and Archaeological Prospection in Apulia, Italy Author(s): Shawn A. Ross, Adela Sobotkova and Gert-Jan Burgers Source: Journal of Field Archaeology, Vol. 34, No. 4 (Winter, 2009), pp. 423-437 Published by: Maney Publishing Stable URL: http://www.jstor.org/stable/25608604 Accessed: 20-11-2015 01:10 UTC REFERENCES Linked references are available on JSTOR for this article: http://www.jstor.org/stable/25608604?seq=1&cid=pdf-reference#references_tab_contents You may need to log in to JSTOR to access the linked references. Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at http://www.jstor.org/page/ info/about/policies/terms.jsp JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. Maney Publishing and Trustees of Boston University are collaborating with JSTOR to digitize, preserve and extend access to Journal of Field Archaeology. http://www.jstor.org This content downloaded from 137.111.13.200 on Fri, 20 Nov 2015 01:10:34 UTC All use subject to JSTOR Terms and Conditions 423 Remote and Archaeological Sensing Prospection inApulia, Italy Shawn A. Ross The University of New South Wales Sydney, New South Wales, Australia Adela Sobotkova The University ofMichigan Ann Arbor, Michigan Gert-Jan Burgers The Royal Netherlands Rome, Italy Institute inRome deployed in combination withground control,archaeological surface survey,and environmental research,remote sensing based upon high-resolutionmultispectral satellite imageryallows large areas to be evaluated efficientlyby a small team ofresearchersand contributesto a betterunderstanding ofan archaeological landscape. In 2007 and 2008, we analyzed ca. 100 sq km of imagery centered onUAmastuola, Italy. Combining the eval uation ofhigh-resolutionmultispectral imagerywith concurrent ground control led to the scatters 29 sites and about significant off-site discoveryof four weeks offieldwork. during Our analysis indicates thatmost of thedetectedfeatures reflect geological conditions amenable topast human habitation rather than subsurfacearchaeological remains. Earlier fieldwork by theMurge Tableland Survey (MTS) provided independent definitionsfor vari ous types sitesand a of large sample of sitesand off-sitescatters in the studyarea. Compari son of our remote-sensing with the results of that surveysuggests that our suc guided efforts cessrate is too high to be explained by random association and also illuminates the strengths When and weaknesses of the respectivemethods, underscoring the need to integrate satellite image analysis withground controland surface survey. Introduction Until recently, high-resolution multispectral imagery, such as QuickBird, has been used to analyze only relative ly small areas (Lasaponara and Masini 2007; Masini and Larger areas have been in vestigated using multispectral but low-resolution imagery or mediumsuch as Landsat to but high-resolution Har 1996; panchromatic imagery likeCORONA (Fowler and Oches 2002; Philip et al. 2002; rower,McCorriston, Lasaponara 2006: 536-537). Wilkinson, Ur, and Casana 2004; Casana and Cothren 2008). Lower-resolution imagery is useful for producing base maps and studying large-scale environmental and ge ological phenomena, while higher-resolution panchromat ic imagery can detect prominent archaeological sites such as tells. Only high-resolution multispectral imagery reveals the relatively small soil marks, crop marks, and shadow marks often associated with subsurface re archaeological mains. Use of high-resolution multispectral allows imagery for the detection of smaller sites, and for the efficient in vestigation and management of large, archaeologically rich landscapes (Madry 2007). The use of high-resolution multispectral imagery as a means of primary archaeological prospection ismethod ologically underdeveloped, and an assessment of the utili tyof all types of imagery remains a pressing need (Kantner 2008). Few projects have combined satellite image analysis with field survey to evaluate the numbers of sites discov a task necessary in order to deter mine the utility of satellite imagery for landscape archaeol im ogy. Madras paper (2007) on the use of QuickBird ered with each method, agery exemplifies this trend, where identified sites are never confirmed through ground control or compared with the results of field survey.Rates of recovery also need This content downloaded from 137.111.13.200 on Fri, 20 Nov 2015 01:10:34 UTC All use subject to JSTOR Terms and Conditions 424 Remote Sensing and Archaeological Prospection inApulia, Italy/Ross,Sobotkova,and Burgers to be related to sensor type and resolution, accounting for different environments and various types of archaeological i \ remains. Our project evaluated 100 sq km of high-resolution established methods of image multispectral imagery using to discover features associated with past human ac analysis was and extended by tivity. Image analysis supplemented V^^ ground control and geological investigation to improve the accuracy and efficiency of site detection, as well as to determine the nature of the relationship between the fea tures visible in the evidence image and archaeological f L'AmastuolaX^^ *^~\ S Jjg] found in the field. The process, built around iterative im age analysis and ground control, led to the discovery of previously unknown sites, shedding new light on settle ment patterns in the environs of L'Amastuola. Results were compared with existing data from the Murge Tableland a Survey (MTS), systematic archaeological surface survey thatwas conducted in a transect across the Salento Isthmus between 2003 and 2007 and included 10 sq km within our area. Variables such as rates of site recovery, time and study labor costs, and the overall character of the results were we assess the relative compared. Here, utility of both ap an extensive in proaches regional investigation, indicating how surface survey and satellite image analysis profitably complement one another. TheUAmastuola Archaeological Project and the Murge Tableland Survey The area investigated in the present project corresponds to the target area of the L'Amastuola Archaeological Pro Paul Crielaard and Gert-Jan Burgers ject, designed by Jan of Vrije Universiteit Amsterdam and begun in 2003 with the aim of investigating the material culture, settlement patterns, and landscape archaeology of the site of L'Amas tuola (figs, i, 2). The MTS, a sister project conducted be tween 2003 and 2007, involved systematic survey of a transect extending from the coastal plain of Taranto into uplands. In 2007, members of this sur also with assisted vey ground control and systematic inves sens tigation of selected features located through remote a ing. The MTS provides comparative dataset for the pre sent remote sensing project. Both the L'Amastuola Archaeological Project and the fit into a research program started by Vrije Univer MTS siteit in 1981 and encompassing amuch wider area?from the Salento Isthmus between Taranto on the Ionian Sea the karsticMurge and Brindisi on the Adriatic, which connects the Salento Peninsula to the rest of Italy. From the beginning, theVri je Universiteit fieldwork in Salento combined excavation, field survey, environmental research, and remote sensing to investigate setdement and landscape evolution in the study 0 Figure 1.Map of southern Italy showing centered on L'Amastuola. 100 200 N i\ the 100 sq km research area region. Initially, Vrije Universiteit fieldwork focused on on the effects of Romanization regional societies (3rd-1st centuries B.C.), but gradually the scope was widened to in clude the impact of earlyGreek colonization (8th-7th cen turies B.C.) and subsequent urbanization?issues that have also motivated research around L'Amastuola. L'Amastuola is considered a key site for the study of a much-debated early Greek colonization, phenomenon among modern classical archaeologists and ancient histori ans. The debate informs the interpretation of the archaeo evidence from excavations in the 1980s by the So logical printendenza dei Beni Archeologici della Puglia and from 2003 onwards by Vrije Universiteit. While some consider the site to be a colonial Greek stronghold in Greek-con trolled territory,others believe that itwas an autonomous settlement with a mixed Greek-indigenous population 1948; Herring 1991; Boardman 1999; D'An The first scenario is thought to demonstrate the aggressive, expansionist nature of early Greek colo nization as well as Greek superiority over the indigenous a population, while the latter supports model of coexis tence and integration. (Dunbabin dria 2002). Setting aside the historical debate, the site occupies one of themost prominent hill peaks in the entire Taranto re gion. Apart from its dominant location, the setdement seems to have been selected with a view to a exploiting resource area of its catchment offers both fer zones; range This content downloaded from 137.111.13.200 on Fri, 20 Nov 2015 01:10:34 UTC All use subject to JSTOR Terms and Conditions Journal ofField Archaeology/Vol.34, 2009 425 IB Figure 2. The Taranto. environs of L'Amastuola. Photograph taken from theMurge tile inland soils for cereal cultivation and a coastal lagoon zone amenable to animal husbandry. It comes as no surprise that early archaeological has es prospection culminating with the intensive MTS tablished that the area was densely inhabited throughout was much more settled in an antiquity. Indeed, the region later than periods, forwhich very few habi tiquity during tation sites have been identified. Early prospection discov ered dozens of small, ancient, rural sites that are spread over the landscape, but clustering in some places in evenly amount of ancient off village-like settlements. The large also suggests that the sitematerial recorded by theMTS area was in exploited intensively, particular during the late Classical and early Hellenistic periods (late 5th through 3rd centuries B.C.). This existing body of settlement infor an ideal test case acquired through survey offered mation looking towards the Gulf of for remote sensing. The results of the present investigation contribute to a fuller understanding of setdement patterns and the environmental conditions underpinning them. SatelliteImage Data satellite image as the This project used a QuickBird basis for analysis. At the time the project was initiated, satellite imagery QuickBird was the highest-resolution with commercially available, optimal panchromatic resolu m and multispectral resolution of 2.44 m. tion of 0.61 information includes separate QuickBird's multispectral red, green, blue, and near-infrared (NIR) bands. Our im age was archival rather than newly tasked, collected on 18 March 2004 (the cost savings offered by archival imagery was justified because there were only modest changes in the landscape over the three-year interval between This content downloaded from 137.111.13.200 on Fri, 20 Nov 2015 01:10:34 UTC All use subject to JSTOR Terms and Conditions image 426 Remote Sensing and Archaeological Prospection inApulia, Italy/Ross,Sobotkova,and Burgers our project). The early acquisition and die beginning of of the date spring image captured vigorous plant growth, increasing the contrast between healthy and stressed vege tation that can reveal archaeological remains. At the same time, plant growth had not proceeded so far bymid-March as to entirely obscure the ground, allowing for the detec tion of soilmarks. A combination of factors including clear a low off-nadir sky, excellent environmental quality, and an unobstructed to combined image with produce angle of A full QuickBird description relatively little distortion. can be found on theDigital Globe website (http:// imagery www. digitalglobe. com/product/product_docs. shtml). Methods Analysis of the imagery began with georeferencing and projection, followed by image overlay and enhancement. Ground control was carried out concurrendy with feature identification because of time constraints and to improve the accuracy of feature identification through immediate feedback from the field. Information from ground control feature identification in the or patterns consistendy denot image, spectral responses or natural features were eliminated from con modern ing was used as to refine ongoing sideration and characteristics of features frequendy associ ated with ancient surfacematerial became clearer. Ground control also provided the location and extent of sites and off-site scatters as defined by theMTS. was performed blind, without Image interpretation of sites previously identified by location of the knowledge theMTS. Only after image analysis and ground control were complete did we compare the sites and off-site scat ters newly discovered through remote sensing with previ was employed in order to ously known sites.This approach remote of results compare the sensing with surface survey a in favor of areas with bias to avoid introducing and known sites. Projection,and Image Processing Georeferencing, Before georeferencing using ground control points, the a root mean square error (RMSE) of 14 m, image had each pixel in the image had a 63% probabil that meaning to 14 m of its actual location ityof being referenced within on the earth's surface. After georeferencing by Samsung of approxi Lim, its accuracy was improved to an RMSE low off the an facilitated result excellent 3 m, by mately nadir angle of the image. The investigators determined that no further correction (such as orthorectification) would be worthwhile since the size and variability of an artifact scat en ter (the most common archaeological phenomenon more After not precise mapping. countered) does require the image was projected onto a local coor georeferencing, dinate system (WGS 84, UTM 33N), ponents of the image were combined and the two com so that the higher layerwas enriched spatial resolution of the panchromatic by information from themultispectral layer. Image Analysis on the Archaeological analysis of satellite images relies or certain and that spectral patterns spatial assumption characteristics of vegetation or topsoil can be correlated remains (Lasaponara and with buried archaeological For 2006b; Lillesand and Kiefer 1994: 20-21). taken from a many decades conventional photographs bird's eye perspective have been used to identify patterns such as soilmarks, crop marks, and shadow marks thatmay Masini indicate past human activity (Crawford 1929; Partington 1983; Riley 1987). Some of these patterns, however, only become visible through manipulation of the various color bands that constitute multispectral satellite imagery (typi Indicators of buried ar cally blue, green, red, and NIR). to spectral analysis include chaeological remains amenable To enhance patterns in soil moisture. and vegetation vigor visible in standard panchromatic or color photographs, the bands inmultispectral satellite imagerymay be manipulat ed manually or through the use of indices (automated mathematical operations on combinations of bands) such as the Normalized Difference Vegetation Index (NDVT) (Lasaponara and Masini 2006a). Our analysis began with band combinations prioritizing red and NIR, as they best reveal differences in vegetation growth sometimes associated with subsurface archaeolog ical remains. The ratio of NIR to red light reflected from in turn revealing plants indicates the health of vegetation, the quality of the soil and substrate. The chlorophyll in and absorbs red. Such healthy vegetation reflects NIR or marks weed may identify aerated, moist, "positive" crop or fertile soils, sometimes revealing filled ditches, graves, or other "cuts" containing disturbed soil that retainwater and nutrients. Conversely, stressed plants are associated with and high red values. These "negative" crop or low NIR weed marks may reveal packed, dry, or infertile soils, some times indicating underground masonry that is depriving water and nutrients (figs. 3B-c, 4A-d) (Parting plants of ton 1983: 183; Masini and Lasaponara 2006). between high NIR values (healthy vegeta were sought tion) and high red values (stressed vegetation) band recombination displaying, primarily through manual for example, NIR as purple and red as green while exclud 4-1-4 band combina ing all other color information (a were then recombination manual of band results The tion). and such as NDVI transformations with supplemented not did the latter Principal Component Analysis, although Contrasts This content downloaded from 137.111.13.200 on Fri, 20 Nov 2015 01:10:34 UTC All use subject to JSTOR Terms and Conditions Journal ofField Archaeology[Vol. 34, 2009 0 ^^ 50 100 ZZZH^^^^H detected in the image. Left column is panchromatic; (4-1-2 right column ismultispectral Figure 3. Features band combination). A-B) Rectilinear feature F1002 proving to be a false positive (protruding bedrock for Soil mark F1014 prominent in the 4-1-2 band combination (confirmed by ground control mation); C-D) as a prehistoric site); E-F) Linear feature (crop mark) F1007 is a false positive (modern pipeline). This content downloaded from 137.111.13.200 on Fri, 20 Nov 2015 01:10:34 UTC All use subject to JSTOR Terms and Conditions N 200 T Meters I 427 428 Remote Sensing and Archaeological Prospection in Apulia, Italy'/Ross,Sobotkova,and Burgers prove useful in our study (Lillesand and Kiefer 1994: In their comprehensive discussions of the use of 536-537). satellite imagery to detect spatially limited ar Masini and chaeological remains, Lasaponara relied heavi an indexwhich further increases the lyon the use ofNDVI, contrast between vigorous and stressed vegetation (Las aponara andMasini 2006a, 2006b, 2007; Masini and Las aponara 2006). Since there is such wide variation inNIR versus red reflectance produced by variable ground cover across our we used NDVI to large study area, primarily areas between bare and and quickly distinguish vegetated to confirm discoveries made through manual band recom multispectral bination crop marks. rather than &s the principal means In addition to detecting crop can also reveal variations sensing be may direcdy associated with ferent soil characteristics (e.g., for detecting and weed marks, remote in soil characteristics that past human activity.Dif texture, chemistry, mois distinct ture, etc.) produce spectral responses visible as "soil in marks55 aerial photography or satellite imagery (Riley on the 1983: 9). The visibility of soilmarks depends largely difference between the reflectance of anthropogenic residues and surrounding surface material. Some soil marks, for example, may appear as lighter spots against the darker background formost of the year (e.g., F1025; see figs. 4A-b). The higher reflectance in this case can proba bly be attributed to differences in soil moisture resulting from the better drainage of disturbed soils and/or the pres ence of subsurface masonry (Ur 2003: 105). In other cases, such as ditches or middens, the buried organic con tentsmay leave a darker on the surface. The level imprint of contrast will depend on particular soil types and season; thin, xeric, and calcareous soils such as those in theMurge are fairly sensitive to fluctuations inmoisture and other dis turbances, facilitating the detectability of soil marks. Soil marks, which are caused by variations in texture and chemical composition, tend to appear across all bands of a multispectral image (Lillesand and Kiefer 1994: 18-19; Ur 2003) As a result, soil marks should be more easily trace able than crop marks, a phenomenon dependant upon sub tie differences in the vegetation health visible only in par ticular band combinations. In our image, some soilmarks, particularly where bedrock had been plowed into surface soils, were readily visible in the panchromatic image (fig. 3A). Elsewhere, soil marks appeared more clearly in a par ticular band combination, as was the case with Feature F1014, a soilmark produced by differences in soil compo sition and moisture retention (Vincenzo Simeone, person al communication 2008) (figs. 3C-d and compare Feature F1017, figs. 4E-f). Determining the nature of soil marks and distinguishing soilmarks from crop or weed marks re quires ground control, especially when considering a large image. A greater degree of certainty about the origin of soil marks can be achieved if ground control takes place soon after image capture (one of the disadvantages of using archival imagery). Idiosyncrasies in our image were selected for ground control based on whether or not they displayed distinctive no that had obvious natural or mod patterns immediately ern Both rectilinear circular and explanation. patterns were scrutinized under theworking assumption thatGreek and Roman sites would have a rectilinear form, while prehis toric sitesmight be circular. Particular attention was paid to features that did not align with themodern field system, roads, or structures such as field division walls. In short, over the course of we analyzing this image found that, given the constraints of time and resources, the most effectiveway to quickly evaluate a large image with wide variations in vegetation cover, topography, and other parameters involved the use of a limited range of manual band combinations (4-2-1; 4-1-2; 4-1-4), paying special attention to idiosyncratic features that did not align with the orientation of modern structures and field divisions. Features were identified visually; in most cases they ap peared as spatial patterns in the intensity of reflectance, usually in band combinations emphasizing the contrast be tween red and NIR. Sometimes we could determine these patterns were crop or soil marks through careful comparison of the panchromatic and multispectral whether images and automated transformations, but inmost cases so doing required ground control. The immediate feed back provided by simultaneous ground control improved image interpretation; spectral responses associated with false positives identified early in the process could be ex cluded as the analysis proceeded, while those associated with ancient surfacematerial could be sought out. Ground Control As noted above, ground control was conducted simul taneously with image analysis and informed feature identi fication in the image. Features were visited to identify any ancient surfacematerial associated with them. Ultimately, one of five were they placed into categories: sites, off-site scatters, ambiguous (significant image anomaly but little or no surfacematerial), false positives, and unassessed. A team consisting of two or three people visited each feature,walked itsperimeter and thenwalked several paths across it.Modern or natural features were noted as such, while features thatwere not obviously modern or natural were fullydocumented. The density of ancient surfacema terial (if present) was systematically recorded. We em same site definition criteria as the MTS (a ployed the This content downloaded from 137.111.13.200 on Fri, 20 Nov 2015 01:10:34 UTC All use subject to JSTOR Terms and Conditions Journal ofFieldArchaeology/Vol.34, 2009 0 50 100 IH^^^^^HM Figure 4. Features detected in the satellite image. Left column is panchromatic. B) and F) are is a Normalized Difference Vegetation (4-1-2 band combination); D) multispectral Index (NDVI); A-B) Rectilinear feature F1025 (confirmed by ground control as a Hel Grid pattern F1023, only visible in the 4-1-2 band combina lenistic/Roman site); C-D) as a Hellenistic/Roman tion and the NDVI reproduced here (confirmed by ground control a a buried site); E-F) Rectilinear feature F1017, promising anomaly perhaps indicating cover structure (ground prevented confirmation). This content downloaded from 137.111.13.200 on Fri, 20 Nov 2015 01:10:34 UTC All use subject to JSTOR Terms and Conditions N 200 t Meters I 429 430 Remote Sensing and Archaeological Prospection inApulia, Italy/Ross,Sobotkova,and Burgers threshold of five sherds per sqm for historical sites and two sherds per sqm for prehistoric sites), and, like theMTS, we corrected for low surface visibility (Burgers, Attema, and van Leusen 1998: 3-4). Correction for surface visibility was particularly important because, unlike a typical surface survey,we could not choose fields based primarily on agri cultural condition and visibility. Again, following the pro cedures of theMTS, off-site scatters that did not meet the site threshold (even after correction) were also recorded. was Wherever ancient material was present, a grab sample collected. The data collected through ground control al lowed us to ascertain whether or not the features identified in the satellite image were associated with ancient materi al, and provided some indication of each site's period of habitation and function. When no material was present, control often explained the origin of these false positives. Several types of false positives were identified in the first days of ground control. Outcroppings of bedrock, modern agricultural improvements or soil conditioning, and un were the most common. As derground pipelines ground ground control proceeded, image patterns associated with these features became readily identifiable, and were eliminated during the subsequent image analysis. Conversely, features identified in the image that proved to be associated with ancient surface material were scrutinized, and a careful search was conducted for similar features thereafter.Nine features identified in the satellite image could not be sub jected to ground control because of inaccessibility or de struction between the date the image was acquired and the time of investigation. These features were excluded from consideration. Results the course of approximately threeweeks of field this iterative process of image analysis, ground control, image review, and subsequent ground control was performed across the entire northern half of the image. The southern half of the image was completed an additional 10 days in June and July2008. In to during over 70 sq km were assessed (fig. 5).One hundred and tal, Over work in July 2007, were identified in the im twenty-three features of interest evaluated 1.45 sq control inventoried. Ground and age areas were omitted, as 114 features. Urban km, including was an area in the extreme southwestern part of the image thatwas deemed very unlikely to yield any ancient remains since itwas a wetiand before drainage in the 20th century and is now subject to intensive use. Ground control determined that 14 image features cor scatters thatmet theMTS's responded to ancient surface definition of a site (aftermodest correction for surface vis ibility). Significant off-site scatterswere additional 15 image features. Another displayed such distinctive and unusual that they remain ambiguous; they had associated with an 13 image features reflectance patterns no obvious expla nation and often low or no surface visibility (e.g., F1017 see figs. As 4E-f). is the case with any archaeological survey, ground control associated with satellite image analysis is not im mune to the it adds problem of site definition. Moreover, to site definition, which complications traditionally de the and of sur boundedness pends upon quality, density, face material. The issue of past human activity associated with chemical residues rather than surface material is of enclosures particular interest in remote sensing. Herding and pastoral camps that contain little surfacematerial are in this category. While in theory such "sites55 should be de tectable through remote sensing under propitious circum stances (repeated use, accumulated deposits, and environ mental conditions amenable to preservation), the impossi bility of their confirmation and dating through non-inva sive techniques prevents conclusive identification. We be lieve that at least some of our "ambiguous55 sites fall into this category. The characteristics of features associated with ancient surfacematerial varied widely across the image.Most strik ingwere unusual patterns likely caused by subsurface struc tures or cuts oriented against the pattern of modern agri cultural divisions. Among confirmed siteswere rectilinear features (F1024, F1025), semicircular and circular features (F1107, F1108, F1036, F1054-1062), andgrids (F1018, F1023; for F1023 see figs. 4C-d). Another group of fea tures associated with surfacematerial was distinguished by a areas of reflectance. Occasionally, particular high NIR a rectilinear in hand with would hand response go spectral pattern visible in other bands. Features F1018 and F1023, visible in the panchromatic image, were accompanied by an intenseNIR response. One general association involved historical sites; such siteswere often accompanied by con trasts in brightness cutting across all bands creating recti linear patterns interpreted as negative crop marks that structures. probably indicate the presence of subsurface one two Three major sites, historical, prehistoric and were and their unusual, intense, spatially recognized by bounded NIR and reflectance (features F1014, F1018, see figs. 3C-d). This characteristic re for F1014 F1054; flectancemay be caused by soil chemistry, but its exact ori to be determined. Feature F1009, a discrete gin has yet re rounded area in the image, produced a high NIR to but site F1014 that of prehistoric flectance similar yield and sta ed no material during ground control. Herding in bling may have been economically important, especially This content downloaded from 137.111.13.200 on Fri, 20 Nov 2015 01:10:34 UTC All use subject to JSTOR Terms and Conditions Journal ofField Archaeology[Vol. 34, 2009 Figure 5. Satellite indicated. the L'Amastuola image of research area analyzed in 2007-2008 areas such as theMurge, but they marginal agricultural leave few durable artifacts (Cribb 1991). Could theNIR reflectance of these features, one prehistoric, one historical, and one unidentified, represent a chemical or mechanical residue characterizing pastoral enclosures, where soil with 431 image features might have been disturbed, phosphate-rich, and moisture retentive as a result of herding? Overall, 14 out of 114 features (12.3%) identified in the satellite image and assessed in the field yielded surface finds thatmet the density criterion for a "site" employed by the This content downloaded from 137.111.13.200 on Fri, 20 Nov 2015 01:10:34 UTC All use subject to JSTOR Terms and Conditions 432 Remote Sensing and Archaeological Prospection inApulia, Italy/Ross,Sobotkova,and Burgers some ancient project. Another 15 features (13.1%) yielded re material below the site threshold, while 13 (11.4%) main features of interest despite the fact that they have not yet yielded any ancient material. Thus, some 25.4% of fea tures yielded significant surface material, while another 11.4% could neither be confirmed nor eliminated from consideration. False Positives Still, some 72 of 114 (63.1%) features were eliminated from consideration after ground control. Such false posi tives further illustrate the strengths and weaknesses of ar chaeological prospection using satellite image analysis. or other activ Many were the result ofmodern agriculture or or natural phenomena (33 or 28.9%). In 23.6%) ity (27 one case (F1007), the feature proved to be an under ground pipeline (figs. 3E-f). Another feature (F1001) consisted of filled ditches once dug for the irrigation of olive trees, but never used. Other features represented the ruins of masserie, the abandoned earlymodern farm com since ancient plexes of southern Italy (F1105 and F1106); occur near itself?sometimes LAmastuola sites?including not were masserie, these features rejected outright, but were thoroughly investigated. Common agricultural prac tices that produce suspicious image features include im of irrigation systems, and portation of topsoil, installation a land amelioration process that involves excavating ditch es in the bedrock, pulverizing the resulting debris, and re to the ditches. Indeed, many of turning the crushed rock of the image (on the coastal half in southern the the fields industrial agriculture is plain, where intensive, large-scale, the norm) had undergone disruptive soil remediation, ren dering archaeological prospection impossible. In short,most of the false positives were similar in na ture to the phenomena sought by archaeological prospec tion: either (modern) crop or weed marks accompanied by or soil marks arising from vari (modern) surfacematerial, ations in the characteristics or composition of the soil. Other features resulted from the presence of modern ma terial on bare ground (total of nine features: piles of mod ern pot sherds, brick fragments, or other rubble). Comparison with theMurge Tableland Survey false positives, the considering the number of identified in the features with sites associated number of be would satellite image proved higher than expected from a random sample. The MTS, which explored a representa tive transect of our study area, yielded an average of 6.3 sites and off-site scatters per sq km (63 sites in total). At Even this rate, an area the size of that analyzed during remote sensing ground control (1.45 sq km) should have pro duced a total of about nine ancient sites and off-site scat ters.The discovery of 29 sites and off-site scatters exceeds the number expected from a randomly chosen area of equal size by more than three times. "False negatives," sites or off-site scatters previously dis but not detected during our image covered by theMTS also reveal the value and limitations of re analysis (fig. 6), mote sensing. Our project encountered 51 such false neg atives.Most remarkably, the large (2.91 ha) necropolis lo cated south of the settlement of UAmastuola could not be located; the exposed tombs cut directly into the limestone and partially covered by pines and macchia (Mediterranean scrub) were invisible in the satellite image. The small size of individual tombs (1.5 x 0.5 m, equiva lent to one or two pixels in the image) combined with the uneven topog bright reflectance of the exposed bedrock, raphy, and patchy surface vegetation, rendered the necrop olis indistinguishable from naturally eroded bedrock out croppings in the vicinity (even now, knowing its location and having visited it several times, none of the investiga tors can distinguish the tombs of this necropolis from un altered bedrock in the image). Similarly, neither the shal bedrock itself is situated, low soil of the hilltop where UAmastuola traces of the nor the vegetation it supported, revealed any structures recovered through excavation; only rectangular the fortificationwall around the sitewas visible as shadow and weed marks produced by macchia protected from the farmers3plow by collapsed masonry (Burgers and Crielaard 2007). Most of the sites and off-site scattersmissed during satellite image analysis, however, consisted of numerous small scatters, a tendency reflected in the difference be tween the median size of scatters discovered through re mote sensing (0.65 ha) versus surface survey (0.1 ha) to de (table i). The smallest tier of sites proved difficult tect through image analysis, even using high-resolution imagery. Twelve image features corresponded to surface concen trations previously defined as sites or off-site scatters by the MTS (out of a total of 63). Curiously, only eight of these 12 features yielded site or off-site sherd densities during The other four produced little if any an ground control. cient surfacematerial (listed as "ground control failure" in Table 1). Since variations in surface visibility are probably not of the sites in question are located in responsible (most fields characterized by well-established perennial agricul in ar a familiar problem ture), this discrepancy highlights re to fail later fieldwork surface may survey: chaeological when sites are resurveyed (Barker results initial produce 1996: 94). The incon 1984; Terrenato and Ammerman This content downloaded from 137.111.13.200 on Fri, 20 Nov 2015 01:10:34 UTC All use subject to JSTOR Terms and Conditions Journal ofField Archaeology[Vol. 34, 2009 ". If CD ? ?A a? @ ? 5 Remote sensing results Murge transect [ |Overlappingsites False negatives Imagefeatures ??????? ^ Q 10Q ^^^ZZZZZZ^D a 40q Meters of satellite sites (2007-2008) in the northeastern part of Figure 6. Comparison image features and MTS the study area. Image features are solid black. The MTS sites that overlap or fall within 25 m of the are solid white; false more than 25 m remotely sensed features negatives (MTS sites beyond the image features) are crosshatched. Solid light gray background represents the transect units of theMTS. This content downloaded from 137.111.13.200 on Fri, 20 Nov 2015 01:10:34 UTC All use subject to JSTOR Terms and Conditions 20Q /\ 433 434 Remote Sensing and Archaeological Prospection inApulia, Italy/Ross,Sobotkova,and Burgers Table 1. Surface surveyand remote sensing comparison (all figuresreflectonly the 100 sq km study area investigatedby both thepresent project and theMTS). Studyarea Areawalked Total features detectedin image (assessed) Sites (newlydiscovered) Off-site scatters (newly discovered) Remote sensingproject MTS 100 sq km ca. 100 sq km 1.45 sq km 10 sq km 123 (114) N/A 14 (8, including1 inMTS transect) 63 (undifferentiated in theprojectGIS) (13, including 2 inMTS 15 Ambiguous of interest Total features False positives False negatives(groundcontrolfailure) 42 72 N/A N/A 51(4) 3 Image feature-MTS overlap Site and off-site scatter size range Site and off-site mean scatter size 0.18-3.30 0.99 ha scatter size Site and off-site median Site and off-site total scatter area 0.65 ha 28.96 ha Labor Time total 0.01-2.91 0.22 ha 63 (undifferentiated in the project GIS) 13 sites and off-site scatters features ha 0.10 ha 18.04 ha ca. 350 person-days 14weeks over fiveseasons ca. 70 person-days 4 weeks over two seasons the presence of small sites in image analysis and ground control). one Conversely, image analysis led to the discovery of new scatters off-site site and two previously unknown transect. Although surveywas more likely within theMTS to find sitesmissed by remote sensing than vice versa, both techniques contributed towards comprehensive prospec seven sites tion. Remote sensing, furthermore, revealed and 11 off-site scatters that lay beyond theMTS transect, can extend the reach of how image analysis demonstrating traditional survey and lead to a fullerunderstanding of the study 12 ha to the size mismatch gruitymay also be partly attributable between (large) image features and (small) average MTS scatters often comprise only a tiny fraction site sizes. MTS of image features, and thusmay have been overlooked by not duplicate the intensity of ground control, which did a theMTS tendency toward underesti (perhaps revealing mating transect) 13 N/A area. remote sensing results demon Comparison ofMTS and strates both the efficiency and idiosyncrasies of satellite im con age analysis in this region. Image analysis and ground trol involved a team averaging three people working for a total of fourweeks (ca. 70 person-days). Considering only in work conducted in the 100 sq km study area, theMTS volved a team of fiveworking two to four weeks per year for five years (ca. 350 person-days). Satellite image analy sis discovered 29 site and off-site scatters (plus 14 ambigu ous features requiring further investigation), while surface was survey discovered 63 scatters. Satellite image analysis at recovering (comparatively) large effective particularly sites, so much so that the total area of scatter inventoried remote sensing exceeds that recovered by surface through survey (28.96 ha versus 18.04 ha) (table i). In part, this treated dis difference is explained by the fact that theMTS crete scatters in close proximity to one another as separate entities, while we considered an image feature containing as a single scatter. multiple concentrations of material Moreover, once ground control demonstrated the presence of ancient surfacematerial, we considered the entire feature to be a site or off-site scatter (in the case of off-site scatter F1034, for example, the area covered by visible scatterwas considerably smaller than the image feature). Overall, however, we found that image features corre scatters. In 2007, sponded reasonably well with surface seven image features associated with site-density surface material were fully and systematically surveyed by theMTS that they employed else team using the same methodology where. This survey found that site-density scatters in and immediately around the image features totaled approxi area of the features. Even if themean, mately 85% of the area discovered through remote scatter total and median, are adjusted downwards to reflect these results, sensing satellite image analysis still tended to locate comparatively a result,we believe that high-resolution im larger sites.As for finding sites somewhat larger than is best suited agery those recovered through systematic surface survey?and that it is a very efficientmeans of accompnshing that task. were often as region, these larger sites or marks soil with sociated crop reflecting particular geo with subsurface archaeo than rather logical phenomena In theUAmastuola logical remains. Environment,Geology,and Image Feature Interpretation Geological conducting are essential for and pedological expertise remote sensing focused on archaeological This content downloaded from 137.111.13.200 on Fri, 20 Nov 2015 01:10:34 UTC All use subject to JSTOR Terms and Conditions Journal ofField Archaeology[Vol. 34, 2009 buried remains; they are the keys to understanding the processes that mediate between the surface, which pro duces the reflection patterns visible in the image, and sub re surface strata potentially containing archaeological a our area sec mains. In geological terms, study comprises tion of thewestern coastal plain of Apulia, extending in land through the transitional zone to theMurge Tableland. The Murge belongs to theApulian karst and ismarked by an average altitude of420 masl rolling hills and ridgeswith van and Leusen 1998: 2, 6). It was (Burgers, Attema, formed by tectonic uplift that separated it from the coastal plain and in the process created a network oigmvine, im pressive canyon-like valleys (Vincenzo Simeone, personal the plateau is only mar communication 2008). Nowadays, as it is neither suited for olive nor cereal ginally exploited, cultivation. Viticulture and orchards prevail in the accessi the rest is covered by macchia and pine ble areas, while groves. Quaternary sediments in the study area display a profile a sandwich: two resembling permeable layers (calcarenite sandstone and limestone) bracket an impermeable clay layer.The top sandstone layer (calcare di Castiglione) is soft and fragile,while the lower limestone (calcare di Gravina) is hard. Water that falls on the surface percolates through the upper sandstone layer and is blocked by the clay (argile di Bradano). Wherever this layer of clay approaches the sur face (as a result of uplift and erosion), it provides low-vol ume but reliable near-surface water sources (Vincenzo van Joolen Simeone, personal communication 2008; 2003: 5-7). Such phenomena are abundant within our study area, especially to the ne of Taranto, and proved to be important factors in interpreting the satellite imagery for archaeological purposes. The geology and associated water cycle of theMurge re gion affects the distribution of archaeological remains. Cli mate in the Salentine and region ismeso-Mediterranean the soil regime is xeric, water indicating deficiency for more than 90 a The Brindisi days year. region mean annu al precipitation is 548 mm, but evaporation exceeds pre cipitation during hot summer months (van Joolen 2003: 4?5). Given these data, it is likely that during antiquity ac cess towater was the principle factor Umiting human habi tation in the region. some features discovered Although through image analysis and associated with ancient surfacematerial likely indicate subsurface remains figs. (e.g., F1023, F1025; 4A-d), themajority do not direcdy reveal traces of past hu man activity. Instead, they correspond to near-surface wa ter sources or areas of high soil moisture. In most cases, these features reveal well-watered areas in zones where the interface between layers of permeable sandstone and im 435 water near the surface (e.g., features permeable clay brings and F1036, F1018, F1024). In other cases, they reflectde filled with water-retaining clayey soils (e.g., fea pressions tures F1009, F1017, F1023, and F1107). revealed locations Thus, our image analysis mosdy to amenable human settlement rather than buried archaeo The majority of sites or off-site scatters dis remains. logical covered through remote sensing were detected due to their association with easily accessible sources ofwater, the lim iting resource in the region. Access towater determines the or even the productivity, possibility, of most agriculture in same At the time, near-surface water sources affect Apulia. vegetation growth and soil moisture, and as a result are readily apparent inmultispectral satellite imagery. Surface material recovered during ground control generally reflect ed habitation rather than burials. In some cases, sites did not liewithin features visible in the image, but insteadwere clustered nearby, a pattern particularly true for smaller scat ters (under 1 ha). Reliable but low-volume near-surface sources produced by the geology of the region likely sup small settlements or seasonal camps. ported to surface survey, Compared image analysis was most successful at finding sites inwell-watered areas of a broad lyxeric region, further supporting an environmental origin of features and associated archaeological sites. In relatively moist regions, the majority of sites discovered through field survey were also located through remote sensing some "new55 sites). Areas near-surface (along with lacking water sources or marked by low soil moisture showed a much lower correlation between our results and those of theMTS, with more false positives and false negatives. a In short, through combination of the nature of remote sensing, the propitious date of image capture, the fact that water is the limiting resource in the region, and the partic ular geological formations that produce near-surface water sources in the study area, image features associated with ancient surfacematerial generally represent environmental conditions conducive to human habitation rather than sub surface archaeological remains. Image analysis produced less successful and more erratic results in areas lacking such water sources. Conclusions Our project used satellite image analysis based on high resolution multispectral imagery to assess a large, archaeo area rich and logically study quickly efficiendy, extending and complementing the results of surface survey. It pro duced positive associations of features visible in the satel lite image and artifact scatters on the ground at a rate over three times higher than would be expected by random chance. Although some of the features identified in the This content downloaded from 137.111.13.200 on Fri, 20 Nov 2015 01:10:34 UTC All use subject to JSTOR Terms and Conditions 436 Remote Sensing and Archaeological Prospection inApulia, Italy/Ross,Sobotkova,and Burgers were the image product of subsurface archaeological re most mains, represent environments conducive to settle ment, particularly zones of near-surface groundwater or was more success moisture-retaining soils. Image analysis sources ful in places containing such water than in uni areas. from surface habitation finds, formly dry Judging siteswere more amenable to detection than funerary sites. Some features, areas with particularly high NIR reflectivi ty,have yet to be explained and would especially benefit from pedological analysis. The differential ability of satellite image analysis to lo cate various types of sites in different environments must be considered when assessing its capacity and limitations Image analysis allows ef ficient assessment of large areas, but its inability to locate certain types of sites in certain environments (such as rock for archaeological reconnaissance. cut tombs or low-impact habitation inuniformly dry areas) that itworks best in combination with other meth ods of prospection, particularly archaeological surface sur vey. Image analysis reflects a multitude of factors, includ nature of cultural residues present, the environ ing the means and geological characteristics of the study area, the cover to reveal subsurface structures, propensity of the land mental and other phenomena that vary by culture and region. The season and time of day inwhich the image is takenmay af fect the visibility of subsurface features through variations and surface re in vegetation growth, soil moisture, flectance. In short, remote sensing has its limitations; dif ferential recovery of archaeological sites argues for remote as complementary sensing and systematic surface survey methods of reconnaissance. can produce results (in Although satellite image analysis terms of the discovery of sites, even some missed by con ventional surface survey) it still lacks a mature, rigorous, to be and systematic methodology. Image analysis needs to on a assessed and scale comprehensively larger deployed across determine rates of site recovery and their variations cultures and natural environments. then (and perhaps even after) remote sensing is best used to complement other means of prospection, such as these limitations, our project has surface survey.Despite and ef remote that demonstrated sensing allows the rapid some subsurface archaeological re ficient identification of mains and, especially, of particular environmental condi tions amenable to ancient habitation. These results suggest that one of themost useful applications of archaeological remote sensing may be to predict areas of human activity near places where a critical resource such as water exists in an otherwise deficient environment. An approach which combines surface survey, geological and environmental and remote sensing will analysis, site location modeling, different archaeological Until produce a powerful tool for regional archaeological prospection. Acknowledgments The authors would like to thank Samsung Lim, School of Surveying and Spatial Analysis, University of New South Wales, Vincenzo Simeone, Department of Environ at Poly mental Engineering and Sustainable Development technicUniversity of Bari, and students from theArchaeo logical Center of the Free University ofAmsterdam, whose assistance gready facilitated this research. We would also like to thank three anonymous reviewers whose comments gready improved this paper. Shawn Ross (Ph.D. 2001, University of Washington) is cur a Lecturer in Ancient Mediterranean and World His rently at in the School and theUniversity tory History of Philosophy ofNew SouthWales, Sydney,Australia. His research interests includepre-Classical Greece, earlyImperial Rome, the history and archaeology of trade, colonization, and imperialism, and theapplication of information technologyto the humanities. address:American Research Center in Sofia, V. Mailing Petleshko 75, Sofia 1500, Bulgaria. E-mail: shawn.ross@unsw.edu.au Adela Sobotkova (MA. 2005, Masaryk University, Brno, Czech Republic) is a Doctoral Candidate in theInterdepart mental Program inClassical Art and Archaeology at the University of Michigan, Ann Arbor. Her research interestsin cludeBlack Sea archaeology, especially the rise of complex soci eties, empiresand frontier environments,and archaeological address: applications of remote sensing and GIS. Mailing American Research Center in Sofia, V. Petleshko 75, Sofia 1500, Bulgaria. E-mail: adelas@umich.edu Gert-Jan Burgers (Ph.D. 1998, Vrije UniversiteitAmster dam, Netherlands) is theHead ofArchaeology and an Assis tant General Director at theRoyal Netherlands Institute in Rome (KNIR) and directs all archaeological projects inApu lia operating under the auspices ofKNIR. His research inter ests include landscape archaeology, archaeological method and Ro theory,Greek-indigenous interaction,Greek colonization, man imperialism, and questions ofacculturation.Mailing address: Koninklijk Nederlands Instituut Rome, Via Omero 10/12, 00197 Roma, Italy. E-mail: Barker, Graeme "The Montarrenti 1984 11: 278-289. Survey, John Boardman, The Greeks Overseas: 1999 York: Thames Burgers, 2007 archeo@knir.it 1982-3 Their Early " ArchaeologicaMedievale Colonies and Trade. New and Hudson. Gert-Jan, and Jean-Paul Crielaard and Indigenous "Greek Colonists This content downloaded from 137.111.13.200 on Fri, 20 Nov 2015 01:10:34 UTC All use subject to JSTOR Terms and Conditions Populations at L'Amas Journal ofField Archaeology/Vol 34, 2009 Italy," Bulletin tuola, Southern 77-114. Gert-Jan, Peter Attema, the Murge. "Walking Burgers, 1998 Antieke and Martijn 82: Beschaeving van Leusen of the Ostuni Interim Report Field Madry, 2007 Remote Crawford, Osbert Guy Stanhope 1929 Air Photography for Archaeologists. tionery Office. Cribb,Roger inArchaeology. Nomads 1991 Press. H. London: M. Sta "Greek Colonization Cambridge: Cambridge University from aNative and Romanization in P. A. J.Attema, van Leusen, Joolen, Martijn in Italian Per Landscape Archaeology: Theory and and Landscape ofField Survey, Land Evaluation Oxford: Ar Perception, Pottery Production and Distribution. 152-159. chaeopress, Methodology 2009 Features Parrington, 1983 2002 1987 Terrenato, 1996 James the Foundation Press. Clarendon of the Greek Colonies to 480 B.C Oxford: J. F. Fowler, Martin 1996 Satellite Imagery in "High-Resolution Archaeological Ap A Russian Satellite Photograph of the Stone plication: hengeRegion,"Antiquity269: 667-671. J.McCorriston, the Roots "Mapping M., and E. A. Oches of Agriculture of Satellite Remote The Application in Southern Edward "Socio-Political Classical in the South Periods: action Model," Kantner, 2008 Recognition to Ancient Change An Application Accordia Italian Iron and Age of the Peer Polity Inter Research Papers 2: 33-54. John "The of Regions: Archaeology to Ubiquitous Spatial 16: 37-81. chaeological Research Toolkit and Nicola Masini Rosa, Lasaponara, 2006a of "Identification Archaeological From Discrete Perspective," Ur, Jason 2003 A. R. Beck, Donoghue, to Soils" in G. naissance on Archaeology. 59-73. Air Photography Nicola, of Cropmarks in Relation ed., The Impact ofAerial Recon London: for British Ar Council and Archaeology. and Albert ofField Archaeology 77: A Northern 102-115. Mesopotamian van Joolen, Esther 2003 Land "Archaeological Suitability of Ancient 2007 91-109. Evaluation. Case Study," Antiquity A Reconstruction of the forVarious Land Uses in Landscapes on the First Millenium B.C.," unpublished Italy Focused Ph.D. Gronin dissertation, Rijksuniversiteit Groningen, gen. Wilkinson, 2004 Tony J., Jason Ur, and Jesse Casana to "From Nucleation Trends Dispersal: tern in the Northern Fertile Crescent" and John F. Cherry, eds., Side-by-Side in theMediterranean Studies Regional Oxbow 189-205. Books, on ing Letters 3: 325-328. the Potential Prospection," 3607-3614. 23: "CORONA SatellitePhotographyandAncientRoad Net works: Satellite Data," Institute of Electrical and Elec QuickBird tronics Engineers Transactions on Geoscience and Remote Sens "On Duckworth. and SiteRecovery in theCecina Valley Survey, '"Visibility Analytical ofAr Based London: J.Ammerman. Journal Buried Remains and N. Galiatsatos of Occurrence S. Maxwell, theNormalized DifferenceVegetation Index (NDVI) from 2006b of Landscape Archaeological Human Transformation "Jour "CORONA SatellitePhotography:An ArchaeologicalAp plicationFrom theMiddle East?Antiquity76: 109-118. Italy"Journal Arabia: Posi Sensing, Global Information tioning System and Geographic System Tech nologies," Archaeological Prospection 9: 35-42. Herring, 1991 Budapest: Michael chaeology, 1948 TheWesternGreeks,TheHistory ofSicilyand SouthItaly from Harrower, 2002 2006. States, April "Remote Sensing" Annual Review ofAnthropology12: Riley, Derrick N. 1983 "The Frequency "Digital Globe," (http://www.digitalglobe.com/product Thomas Lasaponara Related D. N. M. Philip, G., Inc. /product_docs.shtml) Dunbabin, and Rosa Masini, Nicola, 2006 "Satellite-Based Gert-Jan Burgers, Esther van and B. Mater, eds., New Devel opments Globe, 34th Conference, Fargo, United 303-311. Archaeolingua, 105-124. spective" Digital andQuantitativeMethods inArchaeology. Proceedingsofthe nal ofGeophysical Engineering3: 230-235. Francesco DAndria, 2002 Aerial of Google Earth for Archaeological and Site Survey," in JeffreyT. Clark and Emily eds., Digital Discovery: Exploring New Fron Hagemeister, tiers inHuman CAA 2006: Computer Applications Heritage. "An Evaluation and Orthorectification of CORONA Satellite Imagery:Archaeological Applica tionsfromtheNear E&st?Antiquity 82: 732-749. York: Wiley. Prospection 257-282. Jesse, and Jackson Cothren Extraction "Stereo Analysis, DEM New Scott L. H. Survey (Apulia, Southern Italy),"Studi di Antichita 11: Casana, 2008 and Ralph W. Kiefer M., Sensing and Image Interpretation. Thomas Lillesand, 1994 437 of Quickbird Data for Archaeological International Journal of Remote Sensing 27: "Detection ofArchaeologicalCrop Marks byUsing Satel liteQuickBird Multispectral Imagery," Archaeo Journal of logical Science 34: 214-221. This content downloaded from 137.111.13.200 on Fri, 20 Nov 2015 01:10:34 UTC All use subject to JSTOR Terms and Conditions in Settlement in Susan Pat E. Alcock Survey: Comparative World. Oxford: