Federica Cilio takes us through a comparison of images and explains how using several map resources from different time periods can illuminate changes in the archaeological landscape

This case study by Federica Cilio focuses on the analysis of satellite imagery acquired from Google Earth, ESRI, Bing Aerial, CORONA, and Soviet topographic maps, with the aim of showing the different information that each source offers and to demonstrate that the combination of this data allows an accurate and in-depth view of an area of interest. Crucially, the results and methodology can be instrumental to decision makers for the preservation and protection of cultural heritage.

The two examples below, both located in the province of Khatlon, have been selected as a vivid example of how human activities, such as, in this case, construction and agriculture, may result in radical changes in the landscape that may damage or destroy archaeological sites.

Brief background of Nurek dam

Tajikistan was a constituent republic of the Soviet Union from 1929 to 1991 and under their power the country underwent a social and economic transformation. Dams were built exploiting the fast-flowing rivers for two main purposes: the irrigation of agricultural land and as sources of hydroelectric power (Hambly et al. 2019).

The Nurek dam was built on the largest river in the country, the Vakhsh River (a tributary of the Amu Darya) in the Pulsanguin Canyon, 300 m high, in western Tajikistan, about 75 km from the capital Dushanbe. Its construction began in 1961 and the first power generator was put into operation in 1972, the second in 1979. The whole project was completed in 1980. The dam was at that time the highest in the world, later topped in 2013 by the Jinping-I dam in China (Wikipedia, The Free Encyclopaedia, s.v. ‘Nurek Dam’ (accessed 26 October 2020)). During the construction it was estimated that about 5000 people were resettled due to river flooding (Ministry of International Affairs of the Republic of Tajikistan 2020). The city of Nurek was built at the same time to house workers and the reservoir, or Nurek Lake, resulting from the dam has become a popular destination for city people (Caravanistan 2019). The dam meets about 70% of Tajikistan’s electricity needs becoming also a major exporter (Hambly et al. 2019). The water stored in the reservoir, 70 km long and 5 km wide, is transported 14 km through the Dangara irrigation tunnel and used to irrigate about 700 km² of farmland (Ministry of International Affairs of the Republic of Tajikistan 2020; Caravanistan 2019).

The dam is fed by snow and glacier melt from the Tien Shan mountain range (Jalilov et al. 2011, 163) and is therefore subject to low periods of energy production during the winter months. Coal powered energy is used to make up the difference (Eurasianet 2018; Jalilov et al. 2011). ‘Because the country depends so heavily on the Vakhsh for electricity (as well as for agricultural irrigation), the potential impact of global warming on the glaciers that feed the river is a major environmental concern’ (Lindsey 2007).

Multiple satellites and maps have been used to explore the area, offering a view of the landscape both during the construction of the dam and in recent years. These sources have provided essential data for a deeper understanding of the area and its evolution.

Soviet maps and current satellite imagery: a comparison

Figure 1. Comparative map of the Nurek dam using declassified CORONA (DS1110-1153DA084) imagery and Bing Aerial satellite imagery. The red dot marks the city of Nurek; the red polygons indicate potential archaeological elements.

This image has been realised in QGIS comparing CORONA (Ruffner 1995) satellite imagery from 1970 on the left and Bing Aerial from 2016 on the right. The benefit of using imagery from different years, especially in circumstances where the landscape is dramatically changed, is evident. The CORONA image shows the city of Nurek and Vakhsh River during the construction of the dam when the river was still on its original riverbed with potential farmland along the south side of the riverbank. The compared Bing imagery shows a different landscape with a significant widening of the riverbed with the consequent disappearance of the surrounding lands.

If we go only a few kilometres upstream from the reservoir, as shown in Figure 2, the CORONA image shows small villages established along the Vakhsh no longer visible in recent years and the original river course.

Figure 2. Comparative map showing the presence of small villages circled in red in CORONA (DS1110-1153DA084) imagery and on the right, the Vakhsh River in recent years with its reshaped riverbed.

Topographic features

The third source investigated are Soviet maps generated from the late 1960s to the mid-80s. The use of topographic maps gives a more detailed perception of the territory allowing a deeper analysis and assessment of the area. They provide an accurate illustration of natural as well as man-made features that characterised the ground such as relief, vegetation, hydrology, toponomy, transportation and constructions: buildings, urban expansion, channels (irrigation, pipeline, etc.) and much more. As evidenced by the compared images in Figure 3, both generated in the 1970s, these maps prove to be extraordinary in supporting the satellite imagery giving topographic information otherwise unknown, and yet confirming elements on the ground.

Figure 3. Comparative map with declassified CORONA (DS1110-1153DA084) image from 1970 on the left and Soviet map (J-42-55) reprinted in 1979 on the right, both oriented north. The image is a screenshot not created in QGIS because in the software the Soviet maps are out of focus and therefore not suitable for this comparative purpose.

Potential archaeological evidence

Historical topographic maps show, among other things, man-made features sometimes impossible to see from satellite imagery. In Figure 4 below, the same images used in Figure 3 have been proposed again to highlight how, in the same area, the Soviet maps can offer greater information.
In addition to Figure 3, where the comparison showed the presence of villages along the river, the Soviet map in Figure 4 provides further information by showing evidence of archaeological elements (circled in red) near or among villages along the Vakhsh River. These are identified as burial mounds not detectable via satellite imagery. This is just one example of the multitude of components that these maps might offer and their fundamental importance towards a more in-depth analysis is indisputable. For the legend to the maps in English, see the technical manual produced by the Department of the Army (USA) in 1959, available as PDF.

Figure 4. Again, comparative map with declassified CORONA (DS1110-1153DA084) image from 1970 on the left and Soviet map (J-42-55) reprinted in 1979 on the right, both oriented north. The red circles drawn on the topographic map show potential burial mounds not visible from the satellite imagery. Again, the image is a screenshot and was not created in QGIS because in the software the Soviet maps are out of focus and therefore not suitable for this comparative purpose.

Beshkent, Nosiri Kisrav district, southwest Khatlon

‘Many of Tajikistan’s environment problems stem from the agricultural policies of the Soviet era
which converted vast tracts of arid and semi- arid land to cotton cultivation, in a region which
receives very little rainfall and experiences high temperatures in the cotton growing season’ (Department of International Development 2017, 12). This expansion did not take into account the existence or preservation of archaeological sites and farmlands and eventually urban centres developed.

The following examples will show how a cross-referenced approach allows for the extrapolation of a substantial amount of information which can identify and/or confirm the presence of archaeological elements, but also assesses how the development of an area can pose a threat to ancient structures.

Figure 5. Comparative map of area of Beshkent using declassified CORONA (DS1116-1056DA044) imagery from 1972 and Google Satellite (Image © 2020 CNES/Airbus) from 2019.

The comparison of the two satellite images acquired at different periods, provides an immediate understanding of the changes in the landscape over the past several decades. The irrigation system has extensively modified the landscape. At the foot of the mountain, canals have been built which have redesigned the original watercourses, revitalizing the land from arid to fertile. This system has stimulated the intensification of agriculture and the consequent expansion of urban areas.

Zooming to the centre of this comparative map where the archaeological evidence can be identified (Figure 6), CORONA imagery clearly reveals the presence of two settlements. The one to the north located on desert soil along a canal opposite cultivated lands; the one to the south, situated again on arid ground, consisting of a raised tepe (hill) of a rather square shape located in the vicinity of the remains of the foundations of dwellings. The images acquired from Google nearly 50 years later, show a completely different scene where only the tepe survived the agricultural expansion.

Figure 6. Same comparative map as Figure 5 zoomed in on the investigated area. Highlighted in the red circles are evidence of archaeological sites identified as revealed in 1972 and in 2019 (Google Image © 2020 CNES/Airbus).

Topographic features and archaeological evidence

As argued above, the historical topographic maps can be another essential tool to broaden the knowledge of an area of interest and to study any possible land evolution across decades.
In this specific case, the two images below were generated in two different years, 1972 and 1988 respectively (Figure 7). The Soviet map to the right shows the new water system in place and the presence of new construction. Another important element that can be extrapolated from the topographic map is the presence, and therefore, the confirmation of the archaeological element, however represented only as a single ‘burial mound’. This could indicate that already in 1988, the territory underwent physical changes following the creation of the canals, leading to the loss of the remains with only the remnants of the tepe, most likely because of its structural features.

Furthermore, speaking of the architectural component, the Soviet map provides unique information impossible to retrieve through satellite imagery, namely the height of the tepe. The number ‘3’ drawn on the left of the ‘burial mound’ symbols, indicates exactly this.

Figure 7. Comparison between CORONA imagery (DS1116-1056DA044) generate in 1972 to the left and the 1988 Soviet map (J-42-100) to the right both oriented north showing the in the red circles the archaeological evidences. The image is a screenshot not created in QGIS because in the software the Soviet maps are out of focus and therefore not suitable for this comparative purpose.

In light of the elements that topographic maps reveal, comparison with recent satellite images should not be underestimated. In fact, the details shown on the maps not only confirm the presence of ancient features, but also facilitate their identification, especially for the untrained eye (Figure 8).

Figure 8. Comparative map showing to the left Google (Image © 2020 CNES/Airbus) satellite imagery from 2019 and to the right the 1988 Soviet map both oriented north. The red circles reveal the presence of the archaeological evidence. Once again, the image is a screenshot not created in QGIS because in the software the Soviet maps are out of focus and therefore not suitable for this comparative purpose.

Discussion

The table shows the number of sites identified via satellites and maps providing a clear proof of how important is to combine multiple sources.

As the above examples have brought to light, satellite images and topographic maps offer similar evidence and yet unique information. The construction of the Nurek dam and the extensive irrigation system have largely transformed the landscape, producing a large reservoir on the one hand and intensive farming on the other, both visible through Google Satellite, Bing Aerial, and ESRI images. These resources, although of fundamental importance for the exploration of the area in recent years, do not offer a past view of the area. Therefore, the comparison with older images such as CORONA and historical topographic maps, in our case Soviet maps, has made it possible to assess not only the change to which the landscape has been subjected, but also to facilitate the identification of archaeological evidence. Adopting a multi-source approach proved to be essential in achieving a more accurate analysis of the archaeology and will contribute to discourse on predicting consequences to cultural heritage caused by these kinds of changes to the landscape.

references

Caravanistan. 2020. “Nurek Dam and Resorts travel guide.” Caravanistan.

Department for International Development, iMC worldwide. 2017. Growth in Rural Economy and Agriculture in Tajikistan (GREAT). https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/646636/Growth-Rural-Economies-Tajikistan.pdf (accessed 26 October 2020).

Eurasianet. 2018. “Nurek: Tajikistan’s aging king of dams.” Eurasianet. https://eurasianet.org/nurek-tajikistans-aging-king-of-dams (Accessed July 14, 2020).

Hambly, G.R.G., Smith, D.R., Allworth, E., Imshenetsky, A.I., and Sinor, D. 2020. “Tajikistan | People, Religion, History, and Facts.” Encyclopedia Britannica. https://www.britannica.com/place/Tajikistan (Accessed March 23, 2020).

Jalilov, S.-M., DeSutter, T., and Leitch, J.A. 2011. “Impact of Rogun dam on downstream Uzbekistan agriculture.” International Journal of Water Resources and Environmental Engineering 3(8):161–166. https://academicjournals.org/journal/IJWREE/article-abstract/14FD18F54768   

Lindsey, Rebecca. 2007. “Vakhsh River and Lake Nurek, Tajikistan.” NASA Earth Observatory. (accessed 26 October 2020) https://earthobservatory.nasa.gov/images/35999/vakhsh-river-and-lake-nurek-tajikistan

Ministry of International Affairs of the Republic of Tajikistan. 2020. Nurek Dam. Ministry of International Affairs of the Republic of Tajikistan. https://mvd.tj/index.php/en/tajikistan/26776-ner-go-i-bar-i-obii-norak-3 (Accessed July 20, 2020).

Ruffner, Kevin, ed. 1995. Corona: America’s First Satellite Program. Washington DC: History Staff, Center for the Study of Intelligence, Central Intelligence Agency. https://www.cia.gov/library/center-for-the-study-of-intelligence/csi-publications/books-and-monographs/corona.pdf

corona and soviet era maps were accessed via:

CORONA at https://earthexplorer.usgs.gov/

Soviet maps at http://www.etomesto.ru/ for more information on the use of these maps in the CAAL project see Gai Joryayev‘s tutorial on using Soviet maps for identifying archaeological sites and Mahmoud Abdelrazek‘s tutorial on downloading the maps using Python.