Aerial multi-band and multi-polarization radar waves are scattered by phenomena that are strongly associated with human occupation and activities (e.g., materials with dielectric properties, regular geometric shapes, features anomalous to the natural topography and vegetation) in ways that can be used to detect such phenomena. Moreover, synthetic aperture radar (SAR) deployed from satellites and aircraft has been used to detect important archaeological sites on an opportunistic basis over the past two decades. This project sought to devise a systematic method of employing SAR to survey the large areas of land under the stewardship of the Department of Defense (DoD) and other governmental agencies. Until recently, only large features could be detected using SAR. Multi-band and multi-polarization radar have made it possible to detect smaller archaeological sites and features, as well as to provide information about environmental context (e.g., sources of water, slope) that can then be used to understand relationships among sites. Until this research, no collaborative efforts had existed that brought together the broad range of scientific knowledge and technical expertise, such as radar technology, radar phenomenology, archaeology, and resource management, needed to develop radar survey protocols.

The primary objective of this project was to establish protocols for the use of SAR deployed from aircraft to find and classify archaeological sites. A related objective was to identify areas that are potentially important archaeological resources.

Data were collected from flights over the test area, San Clemente Island, which contains a variety of archaeological sites and features typical of the western United States. Data were gathered from both the AIRSAR (Airborne Synthetic Aperature Radar) and GeoSAR (Geographic Synthetic Aperature Radar) platforms along different flight lines, using C, L, and P bands polarized both horizontally and vertically and transmitted at different frequencies. Digital elevation models and images were produced by processing these data. Orthorectification procedures were developed to minimize loss of pertinent data and to maximize accuracy of images. The images were then placed in a geographic information system that contained detailed environmental information and the precise locations and descriptions of previously discovered archaeological sites. Images were analyzed by means of a grid algebra process using algorithms developed during this research to determine signatures for archaeological sites. These analytical protocols also were employed on satellite multispectral images as a means of enhancing site signatures. Signatures were verified by determining what percentage of a set of more than 700 sites, for which precise locations had been independently obtained, fell within signature areas.

Schematic of radar wave phenomenology at typical San Clemente archaeological site

The protocols developed can be used to discover the sites that are both the most archaeologically significant and the most problematic from a management standpoint. The signatures fall within areas that can provide the basis for land-use zoning. These areas are not of the sort that appear in predictive models. Instead, they are the areas where archaeological sites have been sensed and so are empirically based. Therefore, signature areas can form the basis for zoning the landscape at DoD installations and ranges and other managed lands. This zoning can be used immediately for planning. With some additional fieldwork to clarify zone boundaries where these might be unclear, the zones can be used to clear areas for any sorts of activities or to preserve areas where archaeological sites are concentrated. These protocols can be used to accomplish wide-area inventories for archaeological sites in arid and semi-arid environments much more quickly and less expensively than can methods now used for this purpose. (Project Completed - 2006)