Editor’s Note: The following paper is focused on the surveying and mapping of archaeological sites, but also examines a dilemma that surveyors face in nearly all of their work; balancing the highest possible positional quality with affordability and practicality. In an adaptation of their academic paper, Aleksey Korotya and Evgeniy Osadchiy present how they evaluated and tested various technologies for the study of historical fortifications that have featured so prominently in the rich cultural heritage of their home region in north eastern Ukraine.
Geomatics and GIS technologies and their outcomes are widely used among archaeologists in the countries of Western Europe and the USA. The application of highly accurate devices allows them to establish the exact size and configurations of the surrounding terrain.
In some cases, the use of even one total station or GPS device can enable one to answer questions concerning the location and measurement of complex sites such as fortresses, battle fields and burial structures.
In Ukraine such technologies are only starting to be applied, and widespread adoption is often faces financial complications. Through close partnerships with Western European and North American scientific foundations, Ukrainian research institutes conduct studies concerned with cartographic recording of archaeological monuments. Combined usage of several geomatics tools and resources, such as mapping grade GPS recorders and satellite imagery, is one way this is conducted. The margin for error that occurs during such work is entirely within workable limits. This complex method was developed and used by the authors for the study of border fortresses built by Muscovy (outposts of the Tsarist rule of the region) and Rzeczpospolita (traditional name of the Polish State) during the middle 17th century. [1]
What’s necessary for further studies are a complete site survey and the creation of a topographic plan of the site, landscape features, and the positioning of the cultural layers are necessary. They are needed for researchers to visualise the fortification and for further precise mapping of excavated areas of the site. We offer our analysis of tools, resources and methods for the surveying and mapping of these and other archaeological sites of this nature.
Border fortresses are characterised as fortifications which cover a small area of land and where the natural peculiarities of the terrain were maximised and strengthened by defensive structures. Just like for a property survey, one would research as much of the chain of occupation as possible. An overwhelming amount of such fortresses have been built on the location of pre-existing defensive settlements, or Gorodishhe, of previous epochs. These settlements are mentioned often in one of the first supporting documents, describing border outposts of Muscovy, “Knigi Bolshomu Chertezhu”. [2]
During the study of such fortifications, one needs to identify different stages of construction of the monument. Often, existing Gorodishhe selected for the construction of a border fortress would be used almost with no alterations. In such cases the most effective means of identification is stratigraphic study of the site (excavation), as there may be even older layers of foundations and earthworks beneath the site of the (mostly) wooden border forts. The most informative parts of the site in this occasion are the mound, rampart, and moat parts of the earthworks.
Mounds preserved from an earlier time would be used as a “cushion” [foundation] for the construction of a wooden wall. Often the top part of the mound would have been removed or flattened in order to do so. As a result, one needs to establish the remains of previous fortifications of the site. On the other hand, stratigraphic studies of the moats would not yield the same results. Moats are often widened, deepened and cleaned – removing any information of their previous usage. During the research on Gorodishhes with many levels of construction it was discovered that the majority of archaeological material is datable to the early Iron Age, while Ancient Rus. 17th century ceramics were found a lot less often. This can be explained by the fact that border fortresses were mostly seasonal.
The relatively small size and complex terrain of these fortifications require the application of a number of methods of study and combinations of technologies, resources and methods. Precise data can be achieved through the use of survey-grade GPS devices, EDM’s, theodolites and total stations. The topographical recordings achieved using those kinds of technology allows for the creation of an exact plan of the fortification and a map of the surrounding landscape. However, the use of these devices can be prone to complications. Total stations are line of sight; working in a heavily wooded environment can create a number of problems. Dense foliage requires the apparatus to be moved frequently, which increases the time needed for the recordings to be conducted. The same occurs when recording landscape features. As such, the total station is well suited for areas with few trees. The use of any GPS devices faces similar problems as its contact with the satellite cannot be obstructed, as would be the case in a forest or in a deep moat.
One cost-effective method is the use of survey grade GPS devices. After the initial recording, data would be analysed through software packages as ArcGis and MapInfo. The result would be a 3D image of the studied area. The accuracy of this method falls in the range of 1 meter; rough but workable.
Careful documentation and adherence to good field collection procedures can help ensure confidence in meeting this relatively low spatial precision expectation. Such observations allow for a creation of an affordable but useful topographic plan of the archaeological site and the surrounding landscape. However, often archaeological investigations are limited to the mapping of the site only, leaving the surrounding landscape unmapped. As a result the link between the landscape and outlying areas is lost.
Aerial photography can be used as an additional source of information of a site, including the condition of the archaeological monument. However, only the use of vertical photographs may be appropriate. A large proportion of aerial photography is done from helicopters and aircraft which only allow for an angled [oblique] imagery. This creates a distortion of the image and does not reflect the true nature of the landscape. Furthermore, slow flying aircraft are only effective for small scale surveys. For fortresses covering a 2 to 3 hectare area, one needs to utilize aerial photography from a high altitude. [3]
High altitude aerial photographs can be conducted using two types of cameras – digital and infrared. A digital camera with a high quality colour matrix allows the capture of details which can be difficult or prohibitively expensive to observe with a terrestrial survey alone. The use of such images is needed for reconstruction of the terrain and creation of a model of an archaeological monument. However, digital imagery available may not be geo-registered, which requires the surveyor to establish the coordinates of the surveyed area prior to the aerial survey, or in some cases after-the-fact with reprocessing of the imagery. In the processing stages, the [surveyed] points (targets) will be used to position the image on a vector map.
Infrared aerial photography is the most effective for an archaeological monument, especially those with dense vegetation and foliage coverings. The use of an infrared camera ameliorates the issues encountered with a GPS device or a total station- it provides for an image of a fortress which can later be used when creating a topographic map of the area. This is also an advantage of airborne LiDAR for such projects; though this can be an expensive option.
The data collected from electronic and photographic surveys allow us to create a plan of the fortress that contains vector coordinates and coordinates of individual elements. Such surveys provide a way for future referencing and cross examination of fortresses should new elements of their development become available. For the survey of small-scale fortresses, with an area not exceeding 0.5 hectares, one would use a map scale of 1:10 metres. This scale ratio is the most effective for transforming vector data into a raster image.
The application of contour lines could then be applied, for example with an interval of 1 meter or one-half meter, as it is the most effective for recreating elements of the terrain. Using such contours is particularly important when mapping roads leading to a settlement. The creation of such a plan helps analyse and determine of reasons behind the placement of a fortification in a given location, especially considering the important factor of their defensive capabilities.
The city of Sumy, the administrative seat of Sumy Oblast (an administrative region of northeastern Ukraine) is a charming town in the heart of strikingly beautiful, yet relatively “tourist-free” region. With a fine university and burgeoning industries, the town also enjoys a rich cultural heritage; there is great local interest in understanding a history that spans the Palaeolithic, the Neolithic, through early Slavic settlements, occupations by the Poles, the Rus, Muscovy, invasions by Tartars and more. The city was founded around 1650 on the site of the wooden fortification of a Cossack regiment, a border fort built to defend against the Tartars invading from Crimea. While education in surveying and mapping has been very strongly supported, the same economic challenges facing a country that has only recently returned to full independence have made widespread adoption of the latest in geomatics tools, resources, and methods very difficult. Urbanization throughout the revitalized Ukraine has encroached on many cultural sites, and there has been renewed interest in mapping and surveying these sites.
Survey of fortifications of the 17th century can and is conducted using a number of methods which complement each other. If the fortification has a good level of preservation and is clearly visible, one can conduct a survey using traditional survey methods. However, archaeological monuments over the course of three hundred years are usually subject to erosion and plough damage. It is at this point that a more complex method is needed, especially if the terrain does not allow for the use of traditional survey equipment.
In the cases of a collapsed earthwork of a filled-in moat, alternative methods to excavation can be used. To identify the subsurface remains of a fortress, ground-penetrating radar can be employed because it allows for the identification of the difference in the magnetic field of soil at different depths. Ground-penetrating radar is particularly useful when identifying the existence and configuration of a moat, even if it has been fully filled in. A number of conditions should be taken into account when conducting a geo-magnetic survey of an archaeological site. The coordinate system of the survey should be the same as that of the topographic survey of the site and the surrounding area. The optimal place for conducting a geo magnetic survey would be a part of the Gorodishhe free of trees and undergrowth that may obstruct or perturb the movement of the radar. The depth of the cultural layer and features in need of surveying should also be considered. The radar is most effective at the depth of 0.5 metres to 1.5 metres. Considering that the majority of earthworks are located at the depth of 2 metres, the surveyor needs to carefully evaluate the accuracy and reliability of the received data prior to the survey. This especially relates to a multi-layered deposit, as is often the case with earthworks.
The results of such surveys in northwestern Ukraine allowed for a location map of the studied fortresses to be compiled. The positioning of the forts and their topographic specifications allow for a future creation of 3D models of the sites and their relationships. Applying a complex method of combining a number of survey techniques allowed the authors to avoid the shortcomings existent within the individual methods used and had proven the methods ability of accurately documenting the features of archaeological sites. Although the application of such combined methods for this fortification surveys initiative is still in the experimental stages, results produced have allowed the authors to speculate on the potential of the methods for future academic use.
Editor’s Note: This paper and more on these projects will be presented by the authors at an upcoming UNESCO sponsored international conference on the preservation of cultural sites in heavily urbanized areas http://new.sophiakievska.org/en in Kiev Ukraine November 2013.
References:
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