Surfaces from the Visual Past: Recovering High<Emphasis Type="Bold">-</Emphasis>Resolution Terrain Data from Historic Aerial Imagery for Multitemporal Landscape Analysis

Historic aerial images are invaluable sources of aid to archaeological research. Often collected with large-format photogrammetric quality cameras, these images are potential archives of multidimensional data that can be used to recover information about historic landscapes that have been lost to modern development. However, a lack of camera information for many historic images coupled with physical degradation of their media has often made it difficult to compute geometrically rigorous 3D content from such imagery. While advances in photogrammetry and computer vision over the last two decades have made possible the extraction of accurate and detailed 3D topographical data from high-quality digital images emanating from uncalibrated or unknown cameras, the target source material for these algorithms is normally digital content and thus not negatively affected by the passage of time. In this paper, we present refinements to a computer vision-based workflow for the extraction of 3D data from historic aerial imagery, using readily available software, specific image preprocessing techniques and in-field measurement observations to mitigate some shortcomings of archival imagery and improve extraction of historical digital elevation models (hDEMs) for use in landscape archaeological research. We apply the developed method to a series of historic image sets and modern topographic data covering a period of over 70 years in western Sicily (Italy) and evaluate the outcome. The resulting series of hDEMs form a temporal data stack which is compared with modern high-resolution terrain data using a geomorphic change detection approach, providing a quantification of landscape change through time in extent and depth, and the impact of this change on archaeological resources.     

Mapping by matching: a computer vision-based approach to fast and accurate georeferencing of archaeological aerial photographs

To date, aerial archaeologists generally apply simple rectification procedures or more expensive and time-consuming orthorectification algorithms to correct their aerial photographs in varying degrees for geometrical deformations induced by the topographical relief, the tilt of the camera axis and the distortion of the optics. Irrespective of the method applied, the georeferencing of the images is commonly determined with ground control points, whose measurement and identification is a time-consuming operation and often limits certain images from being accurately georeferenced. Moreover, specialised software, certain photogrammetric skills, and experience are required. Thanks to the recent advances in the fields of computer vision and photogrammetry as well as the improvements in processing power, it is currently possible to generate orthophotos of large, almost randomly collected aerial photographs in a straightforward and nearly automatic way. This paper presents a computer vision-based approach that is complemented by proven photogrammetric principles to generate orthophotos from a range of uncalibrated oblique and vertical aerial frame images. In a first phase, the method uses algorithms that automatically compute the viewpoint of each photograph as well as a sparse 3D geometric representation of the scene that is imaged. Afterwards, dense reconstruction algorithms are applied to yield a three-dimensional surface model. After georeferencing this model, it can be used to create any kind of orthophoto out of the initial aerial views. To prove the benefits of this approach in comparison to the most common ways of georeferencing aerial imagery, several archaeological case studies are presented. Not only will they showcase the easy workflow and accuracy of the results, but they will also prove that this approach moves beyond current restrictions due to its applicability to datasets that were previously thought to be unsuited for convenient georeferencing.     

Image‐Based Modelling from Unmanned Aerial Vehicle (UAV) Photogrammetry: An Effective,Low‐Cost Tool for Archaeological Applications

The recording and 3D modelling of complex archaeological sites is usually associated with high capital and logistical costs, because the data acquisition must be performed by specialists using expensive surveying sensors (i.e., terrestrial laser scanners, robotic total stations and/or ground‐penetrating radar). This paper presents a novel, low‐cost, user‐friendly photogrammetric tool for generating high‐resolution and scaled 3D models of complex sites. The results obtained with unmanned aerial vehicle (UAV) photogrammetry of an archaeological site indicate that this approach is semi‐automatic, inexpensive and effective, and that it guarantees quality.     

COMPUTER VISION‐BASED ORTHOPHOTO MAPPING OF COMPLEX ARCHAEOLOGICAL SITES: THE ANCIENT QUARRY OF PITARANHA (PORTUGAL–SPAIN)

Ancient quarries are intriguing archaeological sites, but their detailed recording is complex. This paper presents a cost‐effective approach to mapping of the Roman quarry site of Pitaranha (Portugal–Spain). First, aerial photographs were acquired using a radio‐controlled digital reflex camera attached to a Helikite, which allowed the acquisition of the necessary low‐altitude aerial footage in the very unstable wind conditions above the quarry. Using computer vision algorithms, the resulting set of photographs was semi‐automatically transformed into a Digital Surface Model (DSM) and a corresponding orthophotograph. Besides focusing on the acquisition and processing method, this paper evaluates the accuracy of the generated products. The orthophotograph proved to be satisfactorily accurate for 1:200 hard‐copy mapping.     

Multi-image Photogrammetry for Underwater Archaeological Site Recording: An Accessible,Diver-Based Approach

This article presents a discussion of recent advances in underwater photogrammetric survey, illustrated by case studies in Scotland and Denmark between 2011 and 2013. Results from field trials are discussed with the aim of illustrating practical low-cost solutions for recording underwater archaeological sites in 3D using photogrammetry and using this data to offer enhanced recording, interpretation and analysis. We argue that the availability of integrated multi-image photogrammetry software, highly light-sensitive digital sensors and wide-aperture compact cameras, now allow for simple work flows with minimal equipment and excellent natural colour images even at depths of up to 30 m. This has changed the possibilities for underwater photogrammetric recording, which can now be done on a small scale, through the use of a single camera and automated work flow. The intention of this paper is to demonstrate the quality and versatility of the ‘one camera/ambient light/integrated software’ technique through the case studies presented and the results derived from this process. We also demonstrate how the 3D data generated can be subjected to surface analysis techniques to enhance detail and to generate data-driven fly-throughs and reconstructions, opening the door to new avenues of engagement with both specialists and the wider public.     

From conflict archaeology to archaeologies of conflict: remote survey in Kandahar,Afghanistan

ABSTRACT

Emerging from research with the Afghan Heritage Mapping Partnership, a multi-year project using satellite imagery to detect, record and manage archaeological heritage, this paper examines the potentials of remote-sensing to not only monitor archaeological material culture, but also contemporary materiality as it is violently (re)assembled through conflict. Through systematic remote-sensed archaeological survey using diachronic imagery in Kandahar, Afghanistan, this work expands archaeological understanding of an under-surveyed region while exploring the impact of the region’s expansive military infrastructural footprint on cultural heritage. Further, this research considers the long history of landscapes of control and successive military occupations. Remote survey allows for continued generation of archaeological data during conflict, thereby enabling more thorough heritage management. Finally, this survey demonstrates that, although remote aerial technologies have been criticized as tools of violence, surveillance and control, satellite imagery can be used analytically to generate new understandings of and challenges to military infrastructural reach.     

The use of stereoscopic images taken from a microdrone for the documentation of heritage – An example from the Tuekta burial mounds in the Russian Altay

To analyse, interpret and manage our cultural heritage it is important to have an accurate and realistic representation of it. Documenting this heritage involves geographic techniques such as photogrammetry, for which a lot of rather expensive and extensive platforms are already in use. However, a microdrone, a recently developed unmanned aerial vehicle platform is a cheaper and easy to handle tool. To test the very limits of the microdrone and its accompanying data-acquisition and data-processing software, we collected data from a remote area in Tuekta, in the Russian Altay Mountains. This paper presents the challenges faced during the whole photogrammetric procedure from planning the flights to producing the final deliverables.     

Quantitative analysis of two low-cost aerial photography platforms: A case study of the site of Zagora,Andros, Greece

Aerial photography provides a valuable recording method for archaeological sites and is often underutilized. In the past, aerial photographic platforms were expensive and often required highly specialized equipment. However, with new technology a variety of different platforms are now available. This paper will analyze two low cost aerial photographic platforms used at the Australian Archaeological Institute at Athens/University of Sydney's project at Zagora, on the island of Andros, Greece. Over two years, both kites and drones were used with relative success. Through a review of the application of both systems on the project, along with a quantitative analysis of the cost, transportability, operation and quality of photographs, the strengths and weaknesses of both platforms will be discussed.     

UAV and RPV systems for photogrammetric surveys in archaelogical areas: two tests in the Piedmont region (Italy)

Aerial photogrammetric surveys are usually expensive and the resolution of the acquired images is often limited. For this reason, different innovative systems have been developed and tested in order to perform a photogrammetric survey in an inexpensive way, with high-resolution images. In this context, one of the most promising acquisition techniques is represented by the use of Unmanned Aerial Vehicles (UAVs) equipped with a digital camera.     

Combining photogrammetry and laser scanning for the recording and modelling of the Late Intermediate Period site of Pinchango Alto,Palpa, Peru

This paper describes the 3D modelling of Pinchango Alto, Peru, based on a combination of image and range data. Digital photogrammetry and laser scanning allow archaeological sites to be recorded efficiently and in detail even under unfavourable conditions. In 2004 we documented Pinchango Alto, a typical site of the hitherto poorly studied Late Intermediate Period on the south coast of Peru, with the aim of conducting spatial archaeological analyses at different scales. The combined use of a mini helicopter and a terrestrial laser scanner, both equipped with a camera, allowed a fast yet accurate recording of the site and its stone architecture. In this paper we describe the research background, the 3D modelling based on different image and range data sets, and the resulting products that will serve as a basis for archaeological analysis.     

Near-Infrared Aerial Crop Mark Archaeology: From its Historical Use to Current Digital Implementations

Even though most archaeologists are aware of the crop mark phenomenon and its possible archaeological nature, the information on its occurrence and specific character is, in most cases, obtained by imaging in the visible spectrum. After the Second World War, the occasional use of near-infrared (NIR) sensitive emulsions attributed this kind of invisible imaging with a great potential. However, archaeological NIR imaging always remained restricted due to several reasons not, at least, its complicated workflow and uncertain results. This article wants to delve deeper into the subject, looking at the conventional film-based approach of NIR aerial reconnaissance and its historical use in archaeological crop mark research, after which a current straightforward digital approach will be outlined. By explaining the spectral properties of plants and using examples of recently acquired NIR imagery in comparison with visible frames, it should become clear why the detection and interpretation of crop marks can benefit from low-cost digital NIR imaging in certain situations.     

Multi-temporal archaeological analyses of alluvial landscapes using the photogrammetric restitution of historical flights: a case study of Medellin (Badajoz,Spain)

One of the main challenges affecting the archaeological study of alluvial landscapes is the intensity of change these environments experience over time. Quick and dramatic alterations in geomorphological dynamics and land exploitation determine the visibility and conservation of the archaeological record. This study proposes an approach to the problem of studying these evolving environments based on the analysis and treatment of a series aerial photographs taken between the 1950s and the present day. This paper is particularly interested in looking at the process of photogrammetric restitution and in validating and comparing the digital terrain models and orthoimages produced. The quantitative analysis and visual interpretation of these results can provide valuable information about the transformation of landscapes and factors affecting surface evidence. The intended final result is to develop the ability to map the most problematic or best preserved areas. Nevertheless, it is considered in terms of a relative measure of change magnitude, rather than trying to provide absolute figures.     

数字近景摄影测量在秦始皇陵百戏坑考古中的应用研究

既要保留遗迹在不同阶段的信息资料,又不影响发掘研究工作的继续进行,一直是考古工作者探索研究的问题。为配合秦始皇陵百戏俑坑的考古发掘工作,为后续考古研究和文物遗迹的保护提供必要的基础信息资料,针对大场景考古发掘现场,通过数字全站仪对文物挖掘现场布设的一定数量控制点进行观测获取其三维点位坐标。利用非量测数码相机获取现场多航带序列影像,通过数码相机检校、自动空中三角测量、影像特征提取与影像匹配、数字微分纠正等数字近景摄影测量方法,获取反映发掘现场文物分布情况的数字高程模型(DEM)和正射影像(DOM)数据。在生成的正射影像图上进行文物轮廓线条的提取,获得发掘现场文物的正射投影矢量图。实现文物位置、形状及分布的平面量测。实验证明:该方法不仅可大面积、快速获取文物挖掘现场文物分布的正射投影平面图,实现考古数字制图,而且能保证一定的精度。具有较高的推广应用价值。     

Establishing Best Practices for Photogrammetric Recording During Archaeological Fieldwork

Archaeologists have recently embraced photogrammetry as a low-cost, efficient tool for recording archaeological artifacts, active excavation contexts, and architectural remains. However, no consensus has yet been reached about standard procedures for reliable and metrically accurate photogrammetric recording. The archaeological literature describes diverse equipment and approaches to photogrammetry. The purpose of this article is to open a discussion about when and how photogrammetry should be employed in archaeology in an effort to establish “best practices” for this new method. We focus on the integration of photogrammetry within a comprehensible research plan, the selection of equipment, the appropriate apportionment of labor and time on site, and a rubric for site photography that is conducive to successful and efficient modeling. We conclude that photogrammetric modeling will soon become an indispensable tool in most archaeological applications but should always be implemented in ways that do not place undue burdens on project personnel and budgets and that aid research goals in well-defined ways.     

Cartography of the archaeological surveys taken from an Ikonos stereo-pair: a case study of the territory of Hierapolis in Phrygia (Turkey)

The paper analyses methods and issues connected with the elaboration of Ikonos stereo high-resolution satellite images to create a large-scale cartography for archaeological research. This methodology has been used on an area of the ancient territory of Hierapolis in Phrygia (Turkey), where archaeological surveys, developed by the Italian Archaeological Mission, are in progress. In particular, the study area is situated between the modern villages of Yeniköy and Küçükdereköy, for which neither cartographies suitable for ground surveys nor aerophotogrammetrical covers were available. In this area there are a lot of archaeological remains; in particular, a large Hellenistic and Roman settlement and its necropolises, and also an old Turkish settlement, now destroyed. An Ikonos image was ortho-rectified to obtain a space-map of the entire area. It was used to extract vectorial thematic elements (modern topography, hydrology, archaeological remains and traces, etc.) for the production of maps for archaeological research in the tolerances of a 1:10,000 scale.     

Investigation of past archaeological landscapes using remote sensing and GIS: a multi-method case study from Mount Ida,Crete

Spatial analysis in geoarchaeological applications can be improved by implementing a wider set of geoecological parameters, in order to provide more precise results. The aim of the paper is to show how geoscientific ground-truth and techniques can be adopted for detailed archaeological studies using a comprehensive set of environmental variables that might have influenced ancient settlement patterns. The project focuses on spatial patterns of archaeological sites as well as Bronze Age communication paths in Central Crete by applying a multi-method approach (surveying, remote sensing, DEM analysis, least-cost analysis, candidate site detection, predictive modelling, etc.). In contrast to conventional archaeological GIS applications this enhanced strategy offers promising prospects regarding landscape and settlement modelling.     

Satellite Remote Sensing of Archaeological Vegetation Signatures in Coastal West Africa

This article discusses how archaeological sites in Sierra Leone, and by extension much of West Africa, can be identified through vegetation patterns (vegetation signatures) detectable in very high-resolution (VHR) multispectral satellite imagery. Settlement sites typically have a differing pattern of vegetation from the surrounding landscape, including concentrations of very large trees with sociocultural and historical significance: cotton (Ceiba pentandra) and baobab (Adansonia digitata). These features are conspicuous elements of the landscape both from the ground and in aerial imagery. Two complementary methods of using VHR multispectral satellite imagery are discussed in this paper: visual interpretation and semi-automated subpixel classification. These techniques are aiding ongoing archaeological survey of the Sierra Leone River Estuary. The impact of recently renewed industrial activity at a site of probable archaeological significance is also assessed through visually interpreted VHR satellite imagery.     

Notice of Inscriptions and Antiquities,Discovered at Caerleon

This paper presents some of the background information considered necessary to expand the archaeological uses of aerial photography. Some problems encountered recording archaeological features from the air are discussed but the paper concentrates on the subsequent use of aerial photographs and covers the interpretation and plotting of archaeological features, use of different map scales, and outlines two schemes for the presentation of completed drawings which show air photograph evidence. The uses and potential of morphological analysis are included, as are comments on the relevance of fieldwork to air photograph interpretation.

An appendix considers the application of geophysical techniques to air photograph sites, and the deductions that may be derived from these non-destructive methods.     

Archaeological applications of polynomial texture mapping: analysis,conservation and representation

Polynomial Texture Mapping is an image capture and processing technique that was developed by HP Labs in 2000. It enables the recording and representation of subtle surface details using a standard digital camera and lighting, and software that is free for non-commercial use. Cultural heritage applications have been associated with the technology from its earliest stages, including examples in areas such as cuneiform, numismatics, rock art, lithics and Byzantine art. The paper begins by outlining the technical principles involved. It then brings together the extant work in the field. Through examples developed by the University of Southampton in partnership with a range of UK and international bodies it demonstrates the benefits of the technology in the areas of archaeological analysis, conservation and representation. Finally it considers the future possibilities of this technology and ongoing developments.     

Unmanned Aerial Vehicle (UAV) Survey with Commercial-Grade Instruments: A Case Study from the Eastern Ḫabur Archaeological Survey,Iraq

Low-altitude photography in archaeology is now common practice at the scale of excavations; however, landscape-scale applications are a relatively new endeavor with promising analytical potential. From 2014–2016, an unmanned aerial vehicle (UAV) with a mounted camera was used to document sites recorded as part of the Eastern ?abur Archaeological Survey (E?AS), an archaeological reconnaissance project in western Dohuk Province, Iraqi Kurdistan. The E?AS team documented over 70 archaeological sites with the UAV, from single-phase artifact scatters, to archaeological remains with standing architecture, to tells that cover more than 30 hectares. Representative examples from this survey are presented here to outline the project workflow and primary output data layers, including digital orthomosaics and digital elevation models. The quality and utility of results are then assessed in relationship to available satellite-based data. Methods for analysis and interpretation are then considered to demonstrate applications in landscape archaeology. An A) orthomosaic and B) shaded relief model with surface collection area (in red) of site EHAS-C045 created from photographs taken from a UAV.