Current Development in Archaeological Remote Sensing: A Central European Experience and Evaluation

This article offers thoughts on how current trends are changing the traditional objective of aerial prospection – prehistoric and ancient sites detection and the photographic record – into a more complex aim, namely, the integration of a variety of modern digitally-based, remote-sensing techniques applicable to archaeology into a process that focuses on the study of diachronic developments and synchronic patterns of past settlements. The author presents an evaluation of the current position of remote sensing in the study of the past, mainly from a central European (Czech) perspective, based on his long-term involvement in air survey and landscape archaeology in the Czech Republic. IANSA 2019 ● X/2 ● 155–164 Martin Gojda: Current Development in Archaeological Remote Sensing: A Central European Experience and Evaluation 156 generally allows us to reflect on its complexity. This is true at least when looking at such an intricate component of the world like the Earth’s surface. Its infinitely long evolution has been continually influenced by natural (geologic, climatic, biological) processes, and which human impact has then transformed from what used to be entirely natural into a cultural landscape. These processes have shaped the surface of the Earth and continuously transformed its seemingly stable and unchanging character. The role of archaeology in contemporary Europe has shifted from the more traditional stress on investigation through the excavation of individual sites potentially rich in artefacts/structures/features towards the identification, documentation, mapping and protection of archaeological landscapes for both research objectives and public interest. This orientation corresponds well to the “landscape stream”, one of the most fascinating phenomena, that has attracted recent populations, at least on a European scale. Several works summarising the academic approaches to landscape, and defining the principles of landscape archaeology, have been published since the beginning of this century (e.g., Doneus, 2013, pp.29–38; Fairclough, Møller, eds., 2008; Gojda, 2007; Darvill, Gojda, eds., 2001). This archaeological practice has been more common in Western European countries, but thanks to the increasing number of pan-European projects operating in EU schemes, and due to a certain number of large-scale, state-funded, national research projects in some post-communist countries, it has recently been spreading over this part of Europe as well. Consequently it is non-invasive methods of archaeological research which, since the turn of the 21st century, have taken over the main role in theoretically-motivated (research) projects based on data collected from sites that are not endangered by development. This was explicitly proclaimed as a postulate in the early 1990s when the priority of non-invasive methods was stressed as a point of archaeological ethics at the Valetta Convention for the Protection of the Archaeological Heritage of Europe. Nevertheless, despite the global trends indicating a dominance of non-invasive prospection and field techniques, it is excavation that has maintained its position as the most frequently-applied archaeological method in the heart of Europe, primarily as a legally-supported response to permanent construction activities that have been continuously threatening archaeological heritage since 1990 on a vast scale. Concerning non-invasive methods, ARS, from a historical perspective, is probably the most important. It ranks among the limited number of techniques that have made a contribution to the study and understanding of ancient and historical (medieval, post-medieval, industrial, early modern) periods of the human past. The importance of ARS integration into the study of settlement processes has been compared, for instance, to the invention of the telescope for the study of outer space. Among the methods for gathering/processing/interpreting archaeological data, RS is of high significance and is equal to radiocarbon dating, digital databases, DNA analysis and GIS. At the end of the 1960s and the early 1970s, Leo Deuel, writing about aerial archaeology in his famous book Flights into Yesterday, claimed that “...no other technical advance in archaeology has come so close to fulfilling the goal of recovering intricate cultural contexts, of glimpsing whole prehistoric landscapes, and of capturing a fabric of human existence through the flux of time” (Deuel, 1973, p.26). 2.2 The 1990s – 2000s turnaround: from aerial archaeology to archaeological remote sensing Recent technological development has influenced several archaeological branches, and it is clear that ARS has profited greatly from modern technology: the innovative instruments, devices and techniques invented and produced during the last three decades. It was precisely in this period that the author established aerial archaeology in Bohemia and pushed for the inclusion of this discipline in Czech archaeology. Starting from 1992/3, the position was set in the traditional Crawfordian way of aerial prospection as developed in the 1920s and as such was recently termed “observer-based/directed reconnaissance/aerial surveying” (Verhoeven, Sevara, 2016), “interpretive” (Šmejda, 2017) and “active-interpretive” (Gojda, 2017). It was based on a visual survey of the Earth’s surface from a small aircraft flying at an elevation of c. 300 metres, taking photographs with three analogue, steady cameras and one video camera, navigating visually with the aid of a set of 1:50,000 paper maps, and then, finally, waiting a week or so to find out how successful the mission was after the set of films were developed and images enlarged in a commercial laboratory. A couple of years later, an innovative process was launched that gradually changed aerial archaeology (also referred to as aerial archaeological prospection/reconnaissance/survey) into archaeological remote sensing – a group of techniques/ methods that produced a variety of remotely-sensed data and helped to process and analyse them by sophisticated (digital) procedures: 1. 1993–1995 – the arrival of GNSS/GPS for civilian use and the declassification of the USA’s CORONA satellite imagery; 2. Second half of the 1990s – digital photography introduced to the global market; concerning aerial prospection it greatly simplified the photography process both on board the aircraft (only one camera needed) and after flights (immediate image processing and large-scale digital applicability); 3. 1999 – the launch of the first satellite system (IKONOS) producing images of very high (sub-metre) spatial resolution (in panchro), extremely important for the central European region with a prevalence of small features (pits and small sunken huts at buried, prehistoric and early medieval, settlements); 4. Around 2005 – free access via Google Earth to continuous (seamless) global orthophoto coverage (in the Czech Republic, the first national map server was launched at the same time, with currently accessible imagery taken in five years between 2003–2017; more details follow in the next section); IANSA 2019 ● X/2 ● 155–164 Martin Gojda: Current Development in Archaeological Remote Sensing: A Central European Experience and Evaluation 157 5. 2005–2010 – the beginning of the massive application of airborne laser scanning (ALS) in European archaeology, perhaps the most revolutionary postSecond World War impact on the effective (fast, precise, 3D, digital,....) detection and mapping of our archaeological landscape heritage (this is absolutely true for at least central Europe where ancient, medieval and post-medieval ruined features are preserved as earthworks almost entirely in woodlands). 6. Late 2000s onward – intensified application of image spectrometry using airand spaceborne, hyperspectral data and experimentation with automated (computersupervised) object (i.e. features of archaeological origin) detection from remotely sensed imagery. There is no doubt that these innovations fundamentally changed the traditional image of aerial archaeology, which before this turnaround was – together with the rare application of early satellite imagery and aerial infrared photography (practiced before the 1990s mostly by American scholars, including in their European projects; Madry, 1987) – the exclusive method connected with the study of the (pre)historic landscape from above. The process relegated (traditional) aerial archaeology to the position of just one of several methods integrated into the archaeological remote-sensing “package”. Nevertheless, it is obvious that the integration of modern (digitally-based) sophisticated techniques of ARS with additional field techniques, historical, cartographic and scientific methods/data has a chance to produce more reliable results in the cognitive process focused on the study of diachronic developments and synchronic structures of the components of past settlements and landscapes. 2.3 The potential of remote sensing for central European/Czech archaeology in the 21st century The cognitive process, which in science/research strives to integrate a discipline’s general level with contemporaneous technological achievements and theoretical concepts (paradigms), is never a linear one or one easy to coordinate. The current position of ARS is somewhat strange in that this was formerly a purely detection method predominantly dependent on the observational, physical and interpretative abilities of trained individuals (commonly termed aerial archaeologists), while during the last few years a fundamental change in the ARS agenda (platform) has occurred – primarily as a consequence of the rapid technological development. Today, the dependence of scholars (such as archaeologists, historical geographers, historical environmentalists/ecologists, etc.) on the aerial reconnaissance specialists’ yearly cropmark “harvest” is decreasing. The ability to work with sophisticated software and digital-image