Douglas C. Comer

Detection and Identification of Archaeological Sites and Features Using Synthetic Aperture Radar (SAR) Data Collected from Airborne Platforms

Protocols for archaeological inventory of large areas using synthetic aperture radar (SAR) are presented here. They were developed during a 2002–2005 research project sponsored by a Department of Defense Strategic Environmental Research and Development Program Research Project (SERDP CS-1260) on San Clemente Island, California. Archaeological evidence has established that San Clemente Island has been occupied for almost 10,000 years. Some protocols can also be used with other aerial and satellite datasets, such as those acquired by multispectral sensors. Protocols rely upon algorithms to merge data from multiple flight lines, collection of spatially precise ground data with which to develop signatures, knowledge of site morphology, and elegant statistical treatments of sensing-device return values to automate the development of site signatures (in contrast to using the “trained eye” of remote sensing experts). The Introduction of the article presents the study rationale, SAR basics essential to this research, study-site description, and an overview of fieldwork done. The Results section details eight SAR protocols that were developed: data collection, including look angles, flight lines, and choice of band and polarization; data processing and image production, including orthorectification and the merging of data from multiple flight lines; image post-processing, including statistical techniques and iteration of images; corroborative use of multispectral datasets; spatial modeling; procedures for incorporation into and analysis with GIS; establishment of statistically based site signatures; and procedures for ground verification. In the Discussion, the authors extend some of their findings to archaeological research at San Clemente Island and beyond. The article concludes by highlighting some important management implications for the use of SAR as an archaeological evaluation tool for sizeable land areas. In environments not too dissimilar to those on San Clemente Island, these protocols can produce planning level inventories much more rapidly and inexpensively than field methods commonly used at present can.

Africa, Archaeology and World Heritage

Abstract In this paper we discuss the initiative of the ICOMOS International Committee for Archaeological Heritage Management (ICAHM) to contribute to the UNESCO strategy to create a more representative and balanced World Heritage List. This can be done by concentrating on archaeological sites in Africa that potentially have Outstanding Universal Value. In so doing, we address at the same time the (thematic) under-representation of archaeological sites on the list, as well as the (regional) under-representation of African properties that have been inscribed.

Posterior Probability Modeling and Image Classification for Archaeological Site Prospection: Building a Survey Efficacy Model for Identifying Neolithic Felsite Workshops in the Shetland Islands

The application of custom classification techniques and posterior probability modeling (PPM) using Worldview-2 multispectral imagery to archaeological field survey is presented in this paper. Research is focused on the identification of Neolithic felsite stone tool workshops in the North Mavine region of the Shetland Islands in Northern Scotland. Sample data from known workshops surveyed using differential GPS are used alongside known non-sites to train a linear discriminant analysis (LDA) classifier based on a combination of datasets including Worldview-2 bands, band difference ratios (BDR) and topographical derivatives. Principal components analysis is further used to test and reduce dimensionality caused by redundant datasets. Probability models were generated by LDA using principal components and tested with sites identified through geological field survey. Testing shows the prospective ability of this technique and significance between 0.05 and 0.01, and gain statistics between 0.90 and 0.94, higher than those obtained using maximum likelihood and random forest classifiers. Results suggest that this approach is best suited to relatively homogenous site types, and performs better with correlated data sources. Finally, by combining posterior probability models and least-cost analysis, a survey least-cost efficacy model is generated showing the utility of such approaches to archaeological field survey.

The Measurement by Airborne Synthetic Aperture Radar (SAR) of Disturbance Within the Nasca World Heritage Site

In this paper we report on our use of Synthetic Aperture Radar (SAR) as a means of monitoring the Lines and Geoglyphs of Nasca and Pampas de Jumana World Heritage Site in Peru, where the colossal ground drawings, popularly known as the Nasca Lines, are found. Our research to date indicates that the environment in which the Nasca geoglyphs are found, and the nature of the geoglyphs themselves, are suited perfectly for investigation by SAR. SAR also provides a new and valuable tool for understanding the human activities and natural processes that have damaged the geoglyphs and which, unchecked, will continue to do so in the future. Further, SAR can be used to categorize geoglyphs according to structural differences and similarities in ways that have heretofore not been possible, thereby serving as a basis for a geoglyph catalogue.

Identifying Probable Archaeological Sites on Santa Catalina Island, California Using SAR and Ikonos Data

This chapter describes a method for identifying probable locations of archaeological sites over a wide area based on detecting subtle anomalies in vegetative cover through a statistically based analysis of remotely sensed data from multiple sources. This statistical analysis is further refined and elaborated to compensate for potential slight miss-registrations between the remote sensing data sources and the archaeological site location data. Data quantization approaches (required by the statistical analysis procedure) are explored, and a superior data quantization approach based on a unique image segmentation algorithm is identified. The effectiveness of the method is demonstrated with test data from Santa Catalina Island off the southern California coast.

The Influence of Viewshed on Prehistoric Archaeological Site Patterning at San Clemente Island as Suggested by Analysis of Synthetic Aperture Radar Images

The use of synthetic aperture radar (SAR) imagery collected by the NASA AirSAR platform to detect archaeological site location on San Clemente Island, one of the Southern Channel Islands, has been described in several publications. Here we provide a concise review of the use of SAR for that purpose, as well as a description of how a precise surface model also generated by SAR data was used to examine the spatial distribution of sites by means of viewshed modeling. Results of the direct detection model are evaluated using gain statistics that make use of a recently completed 100% survey of all accessible areas on San Clemente Island. Viewshed analyses generated by use of the surface model suggest a number of economic and ideological factors that might have influenced the distribution of archaeological sites on the island. Among these are intervisibility among locations on both San Clemente Island and nearby Santa Catalina Island that provided the means by which to coordinate crucial substance activities, such as hunting sea mammals, and reinforced the social relationships that were essential to such activities.

Refinement of a Method for Identifying Probable Archaeological Sites from Remotely Sensed Data

To facilitate locating archaeological sites before they are compromised or destroyed, we are developing approaches for generating maps of probable archaeological sites, through detecting subtle anomalies in vegetative cover, soil chemistry, and soil moisture by analyzing remotely sensed data from multiple sources. We previously reported some success in this eort with a statistical analysis of slope, radar, and Ikonos data (including tasseled cap and NDVI transforms) with Students t-test. We report here on new developments in our work, performing an analysis of 8-band multispectral Worldview-2 data. The Worldview-2 analysis begins by computing medians and median absolute deviations for the pixels in various annuli around each site of interest on the 28 band dierence ratios. We then use principle components analysis followed by linear discriminant analysis to train a classier which assigns a posterior probability that a location is an archaeological site. We tested the procedure using leave-one-out cross validation with a second leave-one-out step to choose parameters on a 9,859x23,000 subset of the WorldView-2 data over the western portion of Ft. Irwin, CA, USA. We used 100 known non-sites and trained one classier for lithic sites (n=33) and one classier for habitation sites (n=16). We then analyzed convex combinations of scores from the Archaeological Predictive Model (APM) and our scores. We found that that the combined scores had a higher area under the ROC curve than either individual method, indicating that including WorldView-2 data in analysis improved the predictive power of the provided APM.

Emerging Applications of LiDAR / Airborne Laser Scanning in the Management of World Heritage Sites

Remotely sensed data and imagery have revolutionized the way we understand archaeological sites and landscapes. LiDAR / airborne laser scanning (ALS) has been used to capture the often subtle topographic remnants of previously undiscovered sites even in intensely studied landscapes, and is rapidly becoming a key technology in survey projects with large extents and/or difficult terrain. This paper examines the practical application of this technology to archaeological heritage management, with special attention given to how ALS can support the World Heritage List nomination process and management of WHS archaeological sites and landscapes. It presents a number of examples from published ALS studies alongside case studies from projects undertaken by the authors at Cultural Site Research and Management and the Cultural Site Research and Management Foundation, Baltimore, Maryland, USA. The paper opens with a review of how ALS has been used at established World Heritage Sites, focusing on the Archaeological Ensemble of the Bend in the Boyne, Ireland, and the Angkor Archaeological Site in Cambodia. ALS applications for site prospection and demarcation, and viewshed analysis is explored in this section. Following this, we explore how ALS has been used to support two recent applications: the successfully nominated Monumental Earthworks at Poverty Point, USA and the recently nominated Orheiul Vechi Archaeological Landscape in Moldova. We propose that the detail offered by ALS data greatly strengthens nomination dossiers by emphasizing the outstanding universal value of sites, highlighting significant features and providing greater context to wider landscapes, and is particularly efficacious in delineating site boundaries for legal protection and long-term management. Finally, we conclude with a look at some of the practical considerations involved in the use of ALS, including access and training.