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Reading a difficult landscape from the air. A methodological case-study from a WWII airfield in South Italy
G Model CULHER-3081; No. of Pages 8
ARTICLE IN PRESS Journal of Cultural Heritage xxx (2016) xxx–xxx
Available online at
ScienceDirect www.sciencedirect.com
Reading a difficult landscape from the air. A methodological case-study from a WWII airfield in South Italy Gianluca Cantoro a,∗ , Jeremia Pelgrom b , Tesse D. Stek a a b
University of Leiden, faculty of archaeology, Einsteinweg 22333 CC, Leiden, Netherlands Royal Netherlands Institute Rome, Via Omero 10/12, 00197 Rome, Italy
a r t i c l e
i n f o
Article history: Received 4 July 2015 Accepted 28 September 2015 Available online xxx Keywords: Aerial remote sensing Aerial archaeology Conflict archaeology Aerial photogrammetry
a b s t r a c t The landscape of Basilicata in Southern Italy poses arduous problems for reading the region’s archaeological remains using remote sensing techniques.1 While the nearby plain of Foggia is famous for its wealth of archaeological sites detected from the air (Bradford, 1949; Ceraudo, 2009; Goffredo, 2006), hardly any archaeological traces have been identified in the adjacent Melfese area (North Basilicata). As both regions are characterized by large-scale cereal crop cultivation, this difference cannot be easily explained from agricultural practices alone. Solutions for this conundrum have been proposed by emphasizing the geological and pedological differences between the two regions. While acknowledging that these geopedological circumstances strongly influence the visibility of traces of the past in the Melfese landscape, this paper argues that this is only part of the explanation. By analysing short-term changes in the readability of the traces of the WWII airfield of Venosa (Potenza, Italy), this research highlights the importance of seasonal and climatologic circumstances in remote sensing, as well as human interventions in the landscape. These results complement previous knowledge and signal promising lines of enquiry for disclosing the well-hidden archaeological landscape of the Melfese area and Central-Southern Italy in general. © 2016 Elsevier Masson SAS. All rights reserved.
1. Research aims Targeted reconnaissance flights over Northern Apulia and the Melfese region in Basilicata demonstrated that, even when soil and cultivation-stage conditions seemed optimal for the detection of buried archaeological structures, the two areas responded in entirely different ways (see for instance Fig. 1 for photographs of the two areas taken on a flight of 20 May 2013). While Northern Apulia – a mainly flat, well-draining and intensively cultivated alluvial plain – showed multiple traces of sub-soil structures as both crop-marks and soil-marks, the undulating landscape of Northern
∗ Corresponding author. Tel.: +39 06 326962 29; +31715272392. E-mail addresses: [email protected] (G. Cantoro), [email protected] (J. Pelgrom), [email protected] (T.D. Stek). 1 The research presented here was part of the “Landscapes of Early Roman Colonization” project at Leiden University and the Royal Netherlands Institute in Rome, financed by the NWO. We thank the members of the 485th Bomb Group Association, in particular Gerald Weinstein, Laura Sharpe and Jerry Whiting for their invaluable support. We also thank Christopher Musson and Arthur Hamel for comments on previous drafts of this paper. We also acknowledge the kind collaboration of the Aerofototeca Nazionale (AFN), and Elizabeth Jane Shepherd in particular, at the Istituto Centrale per il Catalogo e la Documentazione (ICCD) in Rome.
Basilicata showed little or no vegetation stress and hence very few potential archaeological marks. Similar observations have been made during aerial reconnaissance campaigns in the past (e.g. [1–4]), thus testifying of the fact that the archaeological landscape of Northern Basilicata is particularly hard to investigate through traditional aerial remote sensing (ARS) approaches. This paper aims to explain the reasons for this situation and to explore some ways of overcoming these difficulties. Moving away from earlier mono-causative explanations, which have focused on the geological properties of the landscape on a regional scale, this paper includes a variety of factors that are analysed on a local scale. By combining the geological and geomorphological information from our case-study with detailed information on recent landscape transformations, present-day agricultural practices and climatologic circumstances, this research aspires to create a more in-depth explanation of the problematic readability of the Melfese landscape. 2. Introduction Although aerial archaeology is surely one of the most effective large-scale non-destructive methods for the understanding of human-landscape interactions (see for instance [5–7]), it is well known that specific ground and weather conditions can alter
http://dx.doi.org/10.1016/j.culher.2015.09.009 1296-2074/© 2016 Elsevier Masson SAS. All rights reserved.
Please cite this article in press as: G. Cantoro, et al., Reading a difficult landscape from the air. A methodological case-study from a WWII airfield in South Italy, Journal of Cultural Heritage (2016), http://dx.doi.org/10.1016/j.culher.2015.09.009
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Fig. 1. Two photographs from the same flight. The first (above), South of Foggia, shows the area’s richness in archaeological information; the second, near Venosa, reveals only major palaeochannels and geological formations. Aerial photographs by Gianluca Cantoro; 20/5/2013.
significantly the visibility of buried archaeological traces, in either positive or negative ways [8]. Yet, it remains difficult to assess the impact these factors may have on the readability of archaeological features in a specific region, as one only rarely knows precisely what is buried underneath the ground, and thus what features could or could not be ideally visible on aerial images. A way to overcome this difficulty is to systematically analyse soil and crop patterns from recent and well-documented archaeological sites [9]. In this paper, such an analysis is offered for a WWII airfield in Venosa (Basilicata, Italy), which is now mostly dismantled and buried underneath the ground. The Melfese area, where the airfield is located, suffered intensive agricultural cultivation over the last half century. Since this agricultural intensification post-dates the WWII structures, these modifications apply (with due differences) as much to the earlier archaeological phases as it does to so-called “pre-industrial” and “conflict” archaeology here under consideration.
By comparing the known lay-out and micro-topography of the airfield with traces visible in aerial photographs taken in different periods, it is possible to analyse in detail which parts of the site are visible under different circumstances. Moreover, establishing the likely causes for the variable “success rates” in the identification of buried features of the airport could also provide valuable information for unveiling much older archaeological landscapes. 3. Methodology For the purposes of this research, we examined all possible field conditions and past agricultural activities that might have altered the current visibility of subsoil archaeological features. These include changes in field boundaries or discontinuities in landuse and several examples are given below to highlight the scale of field activities and the possible effect of these factors on the visibility or actual survival of archaeological features. Moreover,
Please cite this article in press as: G. Cantoro, et al., Reading a difficult landscape from the air. A methodological case-study from a WWII airfield in South Italy, Journal of Cultural Heritage (2016), http://dx.doi.org/10.1016/j.culher.2015.09.009
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Fig. 2. The Venosa airfield in 1944/1945. Adapted from J. Bertam, Just one life. Life and death of Tommy White. Internet resource: http://www.vintagewings.ca (last accessed 5-12-2014).
weather conditions and seasonal rainfall values are considered as determining factors in the visibility of possible traces. The relevant photographic archive material (see Fig. 2 for the oldest – 1944 – image in our dataset) is in quite good condition, with prints of reasonably good quality. The transformations of the landscape after the closure of the airfield in 1945 can be monitored in detail through airborne photographs (dating from 1953 to 2011) and satellite imagery (dating from 2006 to 2012). Original photo-prints have been closely studied in autoptic (naked-eye and loupe-aided), stereographic mode as well as in digital environment. 3.1. Case-study: the WWII airfield near Venosa The semi-permanent airfield of Venosa [10,11] formed part of a series of WWII military airfields within a 25-mile (40 km) radius of Foggia (known as the “Foggia Airfield Complex”, [12,13]). The US Army Corps of Engineers started its construction in September
1943. It had extensive taxiways made of gravel and pebble layers (Fig. 3, left), standing areas, and a steel control tower consisting of a small hut elevated on four tall legs [14]. One of the most important features of the airfield for the purposes of this paper was its runway of Pierced Steel Planking (PSP, still visible in later re-use as parts of doors or fences around Venosa) supported by a gravel foundation layer (Fig. 3, right). This runway was almost 1.2 km (3800 feet) long, with a slope difference of about 15 m (used for short take-off and landing in opposite directions, cf. Fig. 4). The airfield became operational in March 1944 as the base of the 485th Heavy Bombardment Group of the US 15th Air Force. The last combat operations were flown in late April 1945 and the unit returned to the US in May 1945 (Fig. 5), leaving most of the built infrastructure in place. Photographs, documents and diaries made it possible to reconstruct in detail the complete setting of the airfield, including the location of tents, headquarters, chapel and sports field (Fig. 6). This
Fig. 3. Taxiways (left) and take-off and landing strip (right) of the Venosa airport. Adapted from J. Bertam, Just one life. Life and death of Tommy White. Internet resource: http://www.vintagewings.ca (last accessed 5-12-2014).
Please cite this article in press as: G. Cantoro, et al., Reading a difficult landscape from the air. A methodological case-study from a WWII airfield in South Italy, Journal of Cultural Heritage (2016), http://dx.doi.org/10.1016/j.culher.2015.09.009
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Fig. 4. Photogrammetric 3D model of the area draped with a DigitalGlobe satellite image of September 2013. Altitude points are located along the runway of the abandoned WWII airfield near Venosa. Note also the still-visible traces of the airfield’s other facilities (red arrows pointing at the most visible aircraft parking slots).
information, together with the historical images (as single frames and photogrammetric 3D DEM and orthophotos), was digitized in vector and raster format and organized in a GIS. The photogrammetric models, in combination with multi-period imagery, proved useful for understanding the changing patterns of crop and soil marks of the airfield (see [15] for similar methods). For instance, topic discolouration identifiable on images could be related to micro-topographic variations or channelling. The quality of the available prints was not sufficient to allow for a numerical differentiation of 3D models from different years. Nevertheless, single features could be easily interpreted in their diachronic evolution. The gravel and pebble layer upon which the entire airfield was built is the main feature that could be identified over several years, although with varying results, as we will see in more detail below. The irregular presence of this layer on the surface produced lighter
colour stripes in aerial images as a result either of its contrast to the surrounding bare brown soil, or because of the different reaction/life-cycle of vegetation in its proximity. Over the years and as a result of mechanized agricultural activities, this superficial layer was spread following the ploughing patterns, attenuating perceivable chromatic differentiations. The possibility that similar behaviour could have affected earlier archaeological structures in the area is currently under investigation. Below, we analyse two important factors that partially explain the visibility changes on the modern artefact under study. 3.1.1. Agricultural activities and land-use The Venosa area, like most of the South-Italian landscape, has witnessed drastic transformation in the post-WWII period as the result of various agrarian reforms (e.g. the Riforma Agraria of the
Fig. 5. American airmen around the Red Cross van celebrating their last day at Venosa. Note the pebbles in the foreground and the PSP where the aircraft is parked [10]. Unknown photographer.
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Fig. 6. Schematic plan and photo-mosaic of the airfield from US Army archives (courtesy of the veterans of the 485th Bombing Group). The diagram belongs to Sgt. Clarence “Deacon” Miller (nose gunner) and the photomosaic with notations comes from the personal photo-album of Capt. Hadley Huckeby (Air-Photo dpt.).
1950s) and above all by the introduction of a mechanized form of agriculture; this deep-ploughing method (sometimes up to 80 to 100 cm) has had a dramatic impact on the archaeological landscapes [4,16]. The worrying consequences of these ploughing activities on buried structures can be demonstrated clearly by having a closer look at the airfield’s runway near the modern road SS 655. Here, what was initially a clear linear band of lighter-coloured soil, coinciding with the base layer of pebbles and gravel supporting the runway’s PSP, assumes the typical “zig-zag” pattern caused by the alternating direction of mechanized ploughing (Fig. 7). The impact of mechanized agriculture and larger changes in land use is particularly clear in the Western part of the airfield. While
the traces of the airfield are still clearly visible in the 1953 photographs, these gradually fade away and from the 1988 images onwards they are hardly visible at all in the same places, and this cannot be explained solely by differential stages of maturation of local plants. Additionally, this section of the landscape witnessed strong changes in the organization of field boundaries, from a predominant NNW – SSE orientation to a ENE – WSW orientation. These results could be considered as a proxy for large-scale landscape transformations, probably connected with different land use strategies (Fig. 8). This is in strong contrast with the Eastern part of the airfield where the field division system has remained largely stable over time, and where crop marks are consistently conserved.
Fig. 7. DigitalGlobe Satellite image (acquisition date: 27/03/2012) of the runway of the airfield (outlined with red lines) with detail showing the “zig-zag” effect (red arrows) caused by agricultural works.
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Fig. 8. Western part of the airport. Left: aerial image from July 1953. Right: satellite image from March 2012.
Fig. 9. Left satellite image from 18-3-2005. Right satellite image from 27-5-2006.
These differences show how major landscape traces can disappear in only a few decades, while equally demonstrating the worrying impact that modern landscape changes have on buried features. Yet, agricultural intensification in itself does not explain why traditional ARS produces so few results in the Melfese region in comparison to the neighbouring plain of Foggia. However, in combination with the specific geological properties of the landscape (cf. below), especially the relatively thin soils, the effects of these new land use strategies are likely to have had a far more dramatic impact. 3.1.2. Soil-mark and crop-mark visibility The available aerial and satellite images of the airfield show that visibility conditions of crop and soil marks vary strongly and display a remarkable pattern in their seasonal visibility. While May and early June are generally considered good periods for conducting ARS in the Foggia plain [4], this is significantly different in the Venosa airfield region. In our sample, images from June especially produce very few soil and crop marks, while those from May are mediocre at best. Comparisons between the known layout of the
airport and crop-marks shows that the best results were obtained from images of early spring (esp. March) (Fig. 9). This could in part be explained in relation to different phenological cycles. However, as we shall argue below, this situation is probably best explained by a combination of soil composition and climate conditions. As is well known, agricultural practices, planting patterns, the stage of growth in the vegetation, soil composition, and humidity are important factors that affect the present-day visibility of buried structures as crop or soil marks. Deep-rooted crops, such as cereals, often generate the best crop mark results, but only under specific circumstances. Particularly important are the levels of precipitation and the resulting moisture content of the soil [17]. Various studies have firmly established that well-drained soils with relatively high chalk levels will produce the best crop marks,2 while soil-marks
2 Moreover, Evans, in an early publication [9], noted that soil-marks (differences of color in bare soil after ploughing) occur on many soil types but are most common on soils that are highly reflective (such as chalk), in which the underlying subsoil has a sufficiently contrasting color to show clearly in the photograph when ploughed to the surface.
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Fig. 10. The muddy soil in the military camp between the six-man canvas tents [10].
are rarely seen in clay soils [16] because of the limited difference in reflectivity or moisture-retention between the general surface of the fields and the infilling of former ditches, pits or hollows. However, it is known that clay soil can generate crop marks if weather conditions are exceptionally dry [18]. This shows that beside soil composition, climatic variables are also crucial factors.3 The local geological map reveals the presence in the airfield area of compacted layers of pebbles that are embedded in clay or sandstone.4 This composition makes the soil relatively good for agriculture, but due to the shallow depth of the topsoil and the high risk of water-induced surface erosion, it has important limitations concerning the type of cultivation. In fact, these conditions are comparable to those found on clay formations that similarly prevent the water from penetrating into deeper layers [20]. Both soil types thus seriously hamper drainage and consequentially interfere with normal plant growth. For this reason, farmers usually deepplough such fields in order to break up the compact substratum and increase surface drainage. Especially on the hilltops, where soils are usually thinner, it is clear that such hydrological problems occur. However, drainage difficulties also occur in the lower and more flat areas of the Melfese region, where the airfield is located. A number of photographs (for an example, see Fig. 10), as well as the airmen’s diaries, show that the area was recurrently very muddy. For this reason, the runway was constructed of PSP and the floors of the tents were covered with reed mats. As we have noted above, under normal circumstances, soils with these characteristics do not often produce easily readable crop marks. However, especially during very dry periods the situation can improve considerably. Analysis of average rainfall statistics for
the Melfese region,5 indeed suggest that this factor influenced the formation and readability of crop marks in the region. For example, in the last decade February has been consistently dryer than April in the Melfese region, which may explain the different visibility conditions between the March and May images.6 More specifically, the higher visibility spring images had between 3 mm and 14 mm rainfall in the ten days period before they were taken, while the values for the less clear images from May are usually higher, oscillating between 15 mm and 50 mm.
3 For example, Aqdus et. al. demonstrated that “in a damp summer, the water supply necessary for continuing growth will be constantly replenished by rainfall, so plants will not experience moisture stress and no differential growth patterns will be established” [19]. 4 See also the map of granulometry from http://rsdi.regione.basilicata.it. The area of the airport is classified as “fine”, i.e. clay or silt.
5 Datasource: http://www.scia.isprambiente.it. Precipitation figures are averages of measurements of 11 local stations (Forenza, Genazio [2 stations], Spinazzola, Ripacandida, Venosa [2 stations], Potenza, Montemilione, Lavello, Palazzo San Gervasio). 6 On average February 17.04 mm; March 21.9 mm; April 22.4 mm. May 14.4 mm per 10-day period (2000–2014).
4. Conclusions Close analysis of the different data sets available for a microregion in the territory of Venosa yielded important insights on the readability of soil and crop marks in the region. First, the dramatic impact of recent land use strategies has been demonstrated. However, since these agricultural practices occur in the whole of South Italy, this factor does not explain why buried features are particularly hard to detect in the Melfese area in comparison to the nearby Foggia plain. We explain this difference mainly by the geo-pedological properties of this particular landscape, and more in particular by the drainage problems of the conglomerate clay formation, as well as the thinness of the top soil. This combination may also have led to more thorough destruction of the archaeological heritage in this specific landscape. Nevertheless, despite these general and worrying problems, our case study suggests that under extreme vegetation stress conditions, crop mark visibility can increase considerably. An important variable seems to be constituted by weather conditions, in particular rainfall levels.
Please cite this article in press as: G. Cantoro, et al., Reading a difficult landscape from the air. A methodological case-study from a WWII airfield in South Italy, Journal of Cultural Heritage (2016), http://dx.doi.org/10.1016/j.culher.2015.09.009
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The pattern we recognize in the correlation between weather conditions and visibility needs to be further tested in the future. Nevertheless, these preliminary results suggest that dry periods may yield better results in the specific geomorphological area under study. More in general, the opportunity to monitor post-depositional events relating to a well-documented and chronologically welldefined WWII feature, in combination with the information from geology, geomorphology and rainfall statistics, has allowed us to gain valuable information on the aerial visibility – or non-visibility – of buried man-made features in this particular landscape. This guidance from the recent past can now be used in future archaeological studies to provide a better understanding of the interaction between man and the landscape, given the recent large transformations over the last 60 years. References [1] J. Bradford, “Buried Landscapes” in Southern Italy, Antiquity. 23 (1949) 58–72, http://dx.doi.org/10.1017/S0003598X00020056. [2] G. Ceraudo, Sulle tracce della via Traiana. Indagini aerotopografiche da Aecae a Herdonia, Grenzi, Foggia, 2009. [3] R. Goffredo, Aerial archaeology in Daunia (Northern Puglia, Italy). New research and developments, in: Remote Sens. Archaeol., Archaeopress, Oxford, 2006, pp. 541–546. [4] D.N. Riley, New aerial reconnaissance in Apulia, Br. Sch. Rome. 60 (1992) 291–307. [5] O.G.S. Crawford, A. Keiller, Wessex from the Air, Clarendon Press, 1928. [6] O.G.S. Crawford, Some recent air discoveries, Antiquity. 7 (1933) 290–296. [7] G. Willey, Archeology: ancient landscapes: studies in field archaeology, John Bradford. Am. Anthropol. 62 (1960) 176–178.
[8] S. Banton, M. Bowden, T. Daw, D. Grady, S. Soutar, Parchmarks at Stonehenge, July 2013, Antiquity 88 (2014) 733–739. [9] R. Evans, Air photographs for soil survey in Lowland England: soil patterns, Photogramm. Rec. 7 (1972) 302–322. [10] P. Libutti, R. Mancino, I cancelli della guerra 1944/1945. L’aeroporto americano di Venosa, EdiMaior Venosa, Venosa, 2009. [11] J.W. Whiting, Don’t let the blue star turn gold, Tarnaby, Walnut Creek, CA, 2005. [12] M. Maurer, United States, USAF Historical Division, Combat squadrons of the Air Force; World War II, USAF Historical Division, Dept. of the Air Force; for sale by the Supt. of Docs., U.S. Govt. Print. Off., Washington, [Maxwell Air Force Base, Ala.], 1969. [13] Air Force Historical Research Agency, Air Force History Index, Air Force Hist. Index. (n.d.). http://airforcehistoryindex.org/search.php?q=Venosa+ &c=u&h=50&F=1%2F1%2F1940&L=1%2F1%2F1950 (accessed November 20, 2013). [14] H. Kempffer, Harold “Red” Kempffer Diary, 2009. [15] S. Crutchley, Light detection and ranging (lidar) in the Witham Valley, Lincolnshire: an assessment of new remote sensing techniques, Archaeol. Prospect. 13 (2006) 251–257. [16] D. Riley, The technique of air archaeology, Acad. J. Offpr. J. R. Archaeol. Inst. 101 (1946) 1–16. [17] H. Stanjek, J.W.E. Fassbinder, Bodenkundliche Untersuchungen zum Verständnis archäologischer Strukturen im Luftbild, in: K. Hemmeter, M. Petzet (Eds.), Archäol. Prospektion Luftbildarchäologie Geophys., Bayerisches Landesamt f Denkmalpflege, 1996, pp. 249–255. [18] R. Palmer, Seventy-five years v. 90 minutes: implications of the 1996 Bedfordshire vertical aerial survey on our perceptions of clayland archaeology, in: Population Clay Landscape, Tempus Publishing Ltd, 2007, pp. 88–103. [19] S.A. Aqdus, W.S. Hanson, J. Drummond, The potential of hyperspectral and multi-spectral imagery to enhance archaeological cropmark detection: a comparative study, J. Archaeol. Sci. 39 (2012) 1915–1924. [20] F.P. Bonadonna, D. Brocchini, M.A. Laurenzi, C. Principe, G. Ferrara, Stratigraphical and chronological correlations between Monte Vulture volcanics and sedimentary deposits of the Venosa basin, Quat. Int. 47–48 (1998) 87–96, http://dx.doi.org/10.1016/S1040-6182(97)00074-8.
Please cite this article in press as: G. Cantoro, et al., Reading a difficult landscape from the air. A methodological case-study from a WWII airfield in South Italy, Journal of Cultural Heritage (2016), http://dx.doi.org/10.1016/j.culher.2015.09.009
ARTICLE IN PRESS Journal of Cultural Heritage xxx (2016) xxx–xxx
Available online at
ScienceDirect www.sciencedirect.com
Reading a difficult landscape from the air. A methodological case-study from a WWII airfield in South Italy Gianluca Cantoro a,∗ , Jeremia Pelgrom b , Tesse D. Stek a a b
University of Leiden, faculty of archaeology, Einsteinweg 22333 CC, Leiden, Netherlands Royal Netherlands Institute Rome, Via Omero 10/12, 00197 Rome, Italy
a r t i c l e
i n f o
Article history: Received 4 July 2015 Accepted 28 September 2015 Available online xxx Keywords: Aerial remote sensing Aerial archaeology Conflict archaeology Aerial photogrammetry
a b s t r a c t The landscape of Basilicata in Southern Italy poses arduous problems for reading the region’s archaeological remains using remote sensing techniques.1 While the nearby plain of Foggia is famous for its wealth of archaeological sites detected from the air (Bradford, 1949; Ceraudo, 2009; Goffredo, 2006), hardly any archaeological traces have been identified in the adjacent Melfese area (North Basilicata). As both regions are characterized by large-scale cereal crop cultivation, this difference cannot be easily explained from agricultural practices alone. Solutions for this conundrum have been proposed by emphasizing the geological and pedological differences between the two regions. While acknowledging that these geopedological circumstances strongly influence the visibility of traces of the past in the Melfese landscape, this paper argues that this is only part of the explanation. By analysing short-term changes in the readability of the traces of the WWII airfield of Venosa (Potenza, Italy), this research highlights the importance of seasonal and climatologic circumstances in remote sensing, as well as human interventions in the landscape. These results complement previous knowledge and signal promising lines of enquiry for disclosing the well-hidden archaeological landscape of the Melfese area and Central-Southern Italy in general. © 2016 Elsevier Masson SAS. All rights reserved.
1. Research aims Targeted reconnaissance flights over Northern Apulia and the Melfese region in Basilicata demonstrated that, even when soil and cultivation-stage conditions seemed optimal for the detection of buried archaeological structures, the two areas responded in entirely different ways (see for instance Fig. 1 for photographs of the two areas taken on a flight of 20 May 2013). While Northern Apulia – a mainly flat, well-draining and intensively cultivated alluvial plain – showed multiple traces of sub-soil structures as both crop-marks and soil-marks, the undulating landscape of Northern
∗ Corresponding author. Tel.: +39 06 326962 29; +31715272392. E-mail addresses: [email protected] (G. Cantoro), [email protected] (J. Pelgrom), [email protected] (T.D. Stek). 1 The research presented here was part of the “Landscapes of Early Roman Colonization” project at Leiden University and the Royal Netherlands Institute in Rome, financed by the NWO. We thank the members of the 485th Bomb Group Association, in particular Gerald Weinstein, Laura Sharpe and Jerry Whiting for their invaluable support. We also thank Christopher Musson and Arthur Hamel for comments on previous drafts of this paper. We also acknowledge the kind collaboration of the Aerofototeca Nazionale (AFN), and Elizabeth Jane Shepherd in particular, at the Istituto Centrale per il Catalogo e la Documentazione (ICCD) in Rome.
Basilicata showed little or no vegetation stress and hence very few potential archaeological marks. Similar observations have been made during aerial reconnaissance campaigns in the past (e.g. [1–4]), thus testifying of the fact that the archaeological landscape of Northern Basilicata is particularly hard to investigate through traditional aerial remote sensing (ARS) approaches. This paper aims to explain the reasons for this situation and to explore some ways of overcoming these difficulties. Moving away from earlier mono-causative explanations, which have focused on the geological properties of the landscape on a regional scale, this paper includes a variety of factors that are analysed on a local scale. By combining the geological and geomorphological information from our case-study with detailed information on recent landscape transformations, present-day agricultural practices and climatologic circumstances, this research aspires to create a more in-depth explanation of the problematic readability of the Melfese landscape. 2. Introduction Although aerial archaeology is surely one of the most effective large-scale non-destructive methods for the understanding of human-landscape interactions (see for instance [5–7]), it is well known that specific ground and weather conditions can alter
http://dx.doi.org/10.1016/j.culher.2015.09.009 1296-2074/© 2016 Elsevier Masson SAS. All rights reserved.
Please cite this article in press as: G. Cantoro, et al., Reading a difficult landscape from the air. A methodological case-study from a WWII airfield in South Italy, Journal of Cultural Heritage (2016), http://dx.doi.org/10.1016/j.culher.2015.09.009
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Fig. 1. Two photographs from the same flight. The first (above), South of Foggia, shows the area’s richness in archaeological information; the second, near Venosa, reveals only major palaeochannels and geological formations. Aerial photographs by Gianluca Cantoro; 20/5/2013.
significantly the visibility of buried archaeological traces, in either positive or negative ways [8]. Yet, it remains difficult to assess the impact these factors may have on the readability of archaeological features in a specific region, as one only rarely knows precisely what is buried underneath the ground, and thus what features could or could not be ideally visible on aerial images. A way to overcome this difficulty is to systematically analyse soil and crop patterns from recent and well-documented archaeological sites [9]. In this paper, such an analysis is offered for a WWII airfield in Venosa (Basilicata, Italy), which is now mostly dismantled and buried underneath the ground. The Melfese area, where the airfield is located, suffered intensive agricultural cultivation over the last half century. Since this agricultural intensification post-dates the WWII structures, these modifications apply (with due differences) as much to the earlier archaeological phases as it does to so-called “pre-industrial” and “conflict” archaeology here under consideration.
By comparing the known lay-out and micro-topography of the airfield with traces visible in aerial photographs taken in different periods, it is possible to analyse in detail which parts of the site are visible under different circumstances. Moreover, establishing the likely causes for the variable “success rates” in the identification of buried features of the airport could also provide valuable information for unveiling much older archaeological landscapes. 3. Methodology For the purposes of this research, we examined all possible field conditions and past agricultural activities that might have altered the current visibility of subsoil archaeological features. These include changes in field boundaries or discontinuities in landuse and several examples are given below to highlight the scale of field activities and the possible effect of these factors on the visibility or actual survival of archaeological features. Moreover,
Please cite this article in press as: G. Cantoro, et al., Reading a difficult landscape from the air. A methodological case-study from a WWII airfield in South Italy, Journal of Cultural Heritage (2016), http://dx.doi.org/10.1016/j.culher.2015.09.009
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Fig. 2. The Venosa airfield in 1944/1945. Adapted from J. Bertam, Just one life. Life and death of Tommy White. Internet resource: http://www.vintagewings.ca (last accessed 5-12-2014).
weather conditions and seasonal rainfall values are considered as determining factors in the visibility of possible traces. The relevant photographic archive material (see Fig. 2 for the oldest – 1944 – image in our dataset) is in quite good condition, with prints of reasonably good quality. The transformations of the landscape after the closure of the airfield in 1945 can be monitored in detail through airborne photographs (dating from 1953 to 2011) and satellite imagery (dating from 2006 to 2012). Original photo-prints have been closely studied in autoptic (naked-eye and loupe-aided), stereographic mode as well as in digital environment. 3.1. Case-study: the WWII airfield near Venosa The semi-permanent airfield of Venosa [10,11] formed part of a series of WWII military airfields within a 25-mile (40 km) radius of Foggia (known as the “Foggia Airfield Complex”, [12,13]). The US Army Corps of Engineers started its construction in September
1943. It had extensive taxiways made of gravel and pebble layers (Fig. 3, left), standing areas, and a steel control tower consisting of a small hut elevated on four tall legs [14]. One of the most important features of the airfield for the purposes of this paper was its runway of Pierced Steel Planking (PSP, still visible in later re-use as parts of doors or fences around Venosa) supported by a gravel foundation layer (Fig. 3, right). This runway was almost 1.2 km (3800 feet) long, with a slope difference of about 15 m (used for short take-off and landing in opposite directions, cf. Fig. 4). The airfield became operational in March 1944 as the base of the 485th Heavy Bombardment Group of the US 15th Air Force. The last combat operations were flown in late April 1945 and the unit returned to the US in May 1945 (Fig. 5), leaving most of the built infrastructure in place. Photographs, documents and diaries made it possible to reconstruct in detail the complete setting of the airfield, including the location of tents, headquarters, chapel and sports field (Fig. 6). This
Fig. 3. Taxiways (left) and take-off and landing strip (right) of the Venosa airport. Adapted from J. Bertam, Just one life. Life and death of Tommy White. Internet resource: http://www.vintagewings.ca (last accessed 5-12-2014).
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Fig. 4. Photogrammetric 3D model of the area draped with a DigitalGlobe satellite image of September 2013. Altitude points are located along the runway of the abandoned WWII airfield near Venosa. Note also the still-visible traces of the airfield’s other facilities (red arrows pointing at the most visible aircraft parking slots).
information, together with the historical images (as single frames and photogrammetric 3D DEM and orthophotos), was digitized in vector and raster format and organized in a GIS. The photogrammetric models, in combination with multi-period imagery, proved useful for understanding the changing patterns of crop and soil marks of the airfield (see [15] for similar methods). For instance, topic discolouration identifiable on images could be related to micro-topographic variations or channelling. The quality of the available prints was not sufficient to allow for a numerical differentiation of 3D models from different years. Nevertheless, single features could be easily interpreted in their diachronic evolution. The gravel and pebble layer upon which the entire airfield was built is the main feature that could be identified over several years, although with varying results, as we will see in more detail below. The irregular presence of this layer on the surface produced lighter
colour stripes in aerial images as a result either of its contrast to the surrounding bare brown soil, or because of the different reaction/life-cycle of vegetation in its proximity. Over the years and as a result of mechanized agricultural activities, this superficial layer was spread following the ploughing patterns, attenuating perceivable chromatic differentiations. The possibility that similar behaviour could have affected earlier archaeological structures in the area is currently under investigation. Below, we analyse two important factors that partially explain the visibility changes on the modern artefact under study. 3.1.1. Agricultural activities and land-use The Venosa area, like most of the South-Italian landscape, has witnessed drastic transformation in the post-WWII period as the result of various agrarian reforms (e.g. the Riforma Agraria of the
Fig. 5. American airmen around the Red Cross van celebrating their last day at Venosa. Note the pebbles in the foreground and the PSP where the aircraft is parked [10]. Unknown photographer.
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Fig. 6. Schematic plan and photo-mosaic of the airfield from US Army archives (courtesy of the veterans of the 485th Bombing Group). The diagram belongs to Sgt. Clarence “Deacon” Miller (nose gunner) and the photomosaic with notations comes from the personal photo-album of Capt. Hadley Huckeby (Air-Photo dpt.).
1950s) and above all by the introduction of a mechanized form of agriculture; this deep-ploughing method (sometimes up to 80 to 100 cm) has had a dramatic impact on the archaeological landscapes [4,16]. The worrying consequences of these ploughing activities on buried structures can be demonstrated clearly by having a closer look at the airfield’s runway near the modern road SS 655. Here, what was initially a clear linear band of lighter-coloured soil, coinciding with the base layer of pebbles and gravel supporting the runway’s PSP, assumes the typical “zig-zag” pattern caused by the alternating direction of mechanized ploughing (Fig. 7). The impact of mechanized agriculture and larger changes in land use is particularly clear in the Western part of the airfield. While
the traces of the airfield are still clearly visible in the 1953 photographs, these gradually fade away and from the 1988 images onwards they are hardly visible at all in the same places, and this cannot be explained solely by differential stages of maturation of local plants. Additionally, this section of the landscape witnessed strong changes in the organization of field boundaries, from a predominant NNW – SSE orientation to a ENE – WSW orientation. These results could be considered as a proxy for large-scale landscape transformations, probably connected with different land use strategies (Fig. 8). This is in strong contrast with the Eastern part of the airfield where the field division system has remained largely stable over time, and where crop marks are consistently conserved.
Fig. 7. DigitalGlobe Satellite image (acquisition date: 27/03/2012) of the runway of the airfield (outlined with red lines) with detail showing the “zig-zag” effect (red arrows) caused by agricultural works.
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Fig. 8. Western part of the airport. Left: aerial image from July 1953. Right: satellite image from March 2012.
Fig. 9. Left satellite image from 18-3-2005. Right satellite image from 27-5-2006.
These differences show how major landscape traces can disappear in only a few decades, while equally demonstrating the worrying impact that modern landscape changes have on buried features. Yet, agricultural intensification in itself does not explain why traditional ARS produces so few results in the Melfese region in comparison to the neighbouring plain of Foggia. However, in combination with the specific geological properties of the landscape (cf. below), especially the relatively thin soils, the effects of these new land use strategies are likely to have had a far more dramatic impact. 3.1.2. Soil-mark and crop-mark visibility The available aerial and satellite images of the airfield show that visibility conditions of crop and soil marks vary strongly and display a remarkable pattern in their seasonal visibility. While May and early June are generally considered good periods for conducting ARS in the Foggia plain [4], this is significantly different in the Venosa airfield region. In our sample, images from June especially produce very few soil and crop marks, while those from May are mediocre at best. Comparisons between the known layout of the
airport and crop-marks shows that the best results were obtained from images of early spring (esp. March) (Fig. 9). This could in part be explained in relation to different phenological cycles. However, as we shall argue below, this situation is probably best explained by a combination of soil composition and climate conditions. As is well known, agricultural practices, planting patterns, the stage of growth in the vegetation, soil composition, and humidity are important factors that affect the present-day visibility of buried structures as crop or soil marks. Deep-rooted crops, such as cereals, often generate the best crop mark results, but only under specific circumstances. Particularly important are the levels of precipitation and the resulting moisture content of the soil [17]. Various studies have firmly established that well-drained soils with relatively high chalk levels will produce the best crop marks,2 while soil-marks
2 Moreover, Evans, in an early publication [9], noted that soil-marks (differences of color in bare soil after ploughing) occur on many soil types but are most common on soils that are highly reflective (such as chalk), in which the underlying subsoil has a sufficiently contrasting color to show clearly in the photograph when ploughed to the surface.
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Fig. 10. The muddy soil in the military camp between the six-man canvas tents [10].
are rarely seen in clay soils [16] because of the limited difference in reflectivity or moisture-retention between the general surface of the fields and the infilling of former ditches, pits or hollows. However, it is known that clay soil can generate crop marks if weather conditions are exceptionally dry [18]. This shows that beside soil composition, climatic variables are also crucial factors.3 The local geological map reveals the presence in the airfield area of compacted layers of pebbles that are embedded in clay or sandstone.4 This composition makes the soil relatively good for agriculture, but due to the shallow depth of the topsoil and the high risk of water-induced surface erosion, it has important limitations concerning the type of cultivation. In fact, these conditions are comparable to those found on clay formations that similarly prevent the water from penetrating into deeper layers [20]. Both soil types thus seriously hamper drainage and consequentially interfere with normal plant growth. For this reason, farmers usually deepplough such fields in order to break up the compact substratum and increase surface drainage. Especially on the hilltops, where soils are usually thinner, it is clear that such hydrological problems occur. However, drainage difficulties also occur in the lower and more flat areas of the Melfese region, where the airfield is located. A number of photographs (for an example, see Fig. 10), as well as the airmen’s diaries, show that the area was recurrently very muddy. For this reason, the runway was constructed of PSP and the floors of the tents were covered with reed mats. As we have noted above, under normal circumstances, soils with these characteristics do not often produce easily readable crop marks. However, especially during very dry periods the situation can improve considerably. Analysis of average rainfall statistics for
the Melfese region,5 indeed suggest that this factor influenced the formation and readability of crop marks in the region. For example, in the last decade February has been consistently dryer than April in the Melfese region, which may explain the different visibility conditions between the March and May images.6 More specifically, the higher visibility spring images had between 3 mm and 14 mm rainfall in the ten days period before they were taken, while the values for the less clear images from May are usually higher, oscillating between 15 mm and 50 mm.
3 For example, Aqdus et. al. demonstrated that “in a damp summer, the water supply necessary for continuing growth will be constantly replenished by rainfall, so plants will not experience moisture stress and no differential growth patterns will be established” [19]. 4 See also the map of granulometry from http://rsdi.regione.basilicata.it. The area of the airport is classified as “fine”, i.e. clay or silt.
5 Datasource: http://www.scia.isprambiente.it. Precipitation figures are averages of measurements of 11 local stations (Forenza, Genazio [2 stations], Spinazzola, Ripacandida, Venosa [2 stations], Potenza, Montemilione, Lavello, Palazzo San Gervasio). 6 On average February 17.04 mm; March 21.9 mm; April 22.4 mm. May 14.4 mm per 10-day period (2000–2014).
4. Conclusions Close analysis of the different data sets available for a microregion in the territory of Venosa yielded important insights on the readability of soil and crop marks in the region. First, the dramatic impact of recent land use strategies has been demonstrated. However, since these agricultural practices occur in the whole of South Italy, this factor does not explain why buried features are particularly hard to detect in the Melfese area in comparison to the nearby Foggia plain. We explain this difference mainly by the geo-pedological properties of this particular landscape, and more in particular by the drainage problems of the conglomerate clay formation, as well as the thinness of the top soil. This combination may also have led to more thorough destruction of the archaeological heritage in this specific landscape. Nevertheless, despite these general and worrying problems, our case study suggests that under extreme vegetation stress conditions, crop mark visibility can increase considerably. An important variable seems to be constituted by weather conditions, in particular rainfall levels.
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The pattern we recognize in the correlation between weather conditions and visibility needs to be further tested in the future. Nevertheless, these preliminary results suggest that dry periods may yield better results in the specific geomorphological area under study. More in general, the opportunity to monitor post-depositional events relating to a well-documented and chronologically welldefined WWII feature, in combination with the information from geology, geomorphology and rainfall statistics, has allowed us to gain valuable information on the aerial visibility – or non-visibility – of buried man-made features in this particular landscape. This guidance from the recent past can now be used in future archaeological studies to provide a better understanding of the interaction between man and the landscape, given the recent large transformations over the last 60 years. References [1] J. Bradford, “Buried Landscapes” in Southern Italy, Antiquity. 23 (1949) 58–72, http://dx.doi.org/10.1017/S0003598X00020056. [2] G. Ceraudo, Sulle tracce della via Traiana. Indagini aerotopografiche da Aecae a Herdonia, Grenzi, Foggia, 2009. [3] R. Goffredo, Aerial archaeology in Daunia (Northern Puglia, Italy). New research and developments, in: Remote Sens. Archaeol., Archaeopress, Oxford, 2006, pp. 541–546. [4] D.N. Riley, New aerial reconnaissance in Apulia, Br. Sch. Rome. 60 (1992) 291–307. [5] O.G.S. Crawford, A. Keiller, Wessex from the Air, Clarendon Press, 1928. [6] O.G.S. Crawford, Some recent air discoveries, Antiquity. 7 (1933) 290–296. [7] G. Willey, Archeology: ancient landscapes: studies in field archaeology, John Bradford. Am. Anthropol. 62 (1960) 176–178.
[8] S. Banton, M. Bowden, T. Daw, D. Grady, S. Soutar, Parchmarks at Stonehenge, July 2013, Antiquity 88 (2014) 733–739. [9] R. Evans, Air photographs for soil survey in Lowland England: soil patterns, Photogramm. Rec. 7 (1972) 302–322. [10] P. Libutti, R. Mancino, I cancelli della guerra 1944/1945. L’aeroporto americano di Venosa, EdiMaior Venosa, Venosa, 2009. [11] J.W. Whiting, Don’t let the blue star turn gold, Tarnaby, Walnut Creek, CA, 2005. [12] M. Maurer, United States, USAF Historical Division, Combat squadrons of the Air Force; World War II, USAF Historical Division, Dept. of the Air Force; for sale by the Supt. of Docs., U.S. Govt. Print. Off., Washington, [Maxwell Air Force Base, Ala.], 1969. [13] Air Force Historical Research Agency, Air Force History Index, Air Force Hist. Index. (n.d.). http://airforcehistoryindex.org/search.php?q=Venosa+ &c=u&h=50&F=1%2F1%2F1940&L=1%2F1%2F1950 (accessed November 20, 2013). [14] H. Kempffer, Harold “Red” Kempffer Diary, 2009. [15] S. Crutchley, Light detection and ranging (lidar) in the Witham Valley, Lincolnshire: an assessment of new remote sensing techniques, Archaeol. Prospect. 13 (2006) 251–257. [16] D. Riley, The technique of air archaeology, Acad. J. Offpr. J. R. Archaeol. Inst. 101 (1946) 1–16. [17] H. Stanjek, J.W.E. Fassbinder, Bodenkundliche Untersuchungen zum Verständnis archäologischer Strukturen im Luftbild, in: K. Hemmeter, M. Petzet (Eds.), Archäol. Prospektion Luftbildarchäologie Geophys., Bayerisches Landesamt f Denkmalpflege, 1996, pp. 249–255. [18] R. Palmer, Seventy-five years v. 90 minutes: implications of the 1996 Bedfordshire vertical aerial survey on our perceptions of clayland archaeology, in: Population Clay Landscape, Tempus Publishing Ltd, 2007, pp. 88–103. [19] S.A. Aqdus, W.S. Hanson, J. Drummond, The potential of hyperspectral and multi-spectral imagery to enhance archaeological cropmark detection: a comparative study, J. Archaeol. Sci. 39 (2012) 1915–1924. [20] F.P. Bonadonna, D. Brocchini, M.A. Laurenzi, C. Principe, G. Ferrara, Stratigraphical and chronological correlations between Monte Vulture volcanics and sedimentary deposits of the Venosa basin, Quat. Int. 47–48 (1998) 87–96, http://dx.doi.org/10.1016/S1040-6182(97)00074-8.
Please cite this article in press as: G. Cantoro, et al., Reading a difficult landscape from the air. A methodological case-study from a WWII airfield in South Italy, Journal of Cultural Heritage (2016), http://dx.doi.org/10.1016/j.culher.2015.09.009