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Computational analysis of satellite images detects new evidence of previously overlooked human settlements

an ASTER image of the Bronze Age city of

Researchers Jason Ur and Bjoern Menze used computers to analyze an ASTER image (left) of the Bronze Age city of Hamoukar (ca. 2600 to 2000 B.C.), located in northeastern Syria's Khabur Basin, to find areas of human occupation (right, indicated by orange clusters). Their method allows them to find smaller sites, in addition to ones that form large mounds. (Courtesy Jason Ur, Harvard University, and Bjoern Menze, Massachusetts Institute of Technology)

Since the early twentieth century, archaeologists have relied on aerial photography as a technique to locate possible sites without having to physically survey vast areas. Signs of human habitation in aerial photos derive from the presence of habitation mounds and from changes in soil color tied to the presence of anthrosols—soil that has been modified by human activity.

While inarguably useful for finding sites, this type of remote sensing analysis is time-consuming and tedious, requiring researchers to pore over hundreds of images to identify potential candidate sites for excavation. Further, only large mounds are discernible in aerial photos. Thus, smaller sites are tough to detect, the relationships between different settlements are hard to decipher, and the expanse of a civilization is difficult to determine. In order to fill in the blanks, archaeologist Jason Ur of Harvard University and Massachusetts Institute of Technology computer scientist Bjoern Menze have now turned the job of image analysis over to computers. Their method uses images taken by ASTER, the Advanced Spaceborne Thermal Emission and Reflection Radiometer instrument aboard NASA's Terra satellite, originally launched in 1999 to observe changes in the Earth's climate. Their approach takes advantage of the fact that anthrosols and the soil around them reflect light differently.

As a starting point, Ur and Menze focused on ASTER images of the Early Bronze Age city of Hamoukar in northeastern Syria, which Ur had surveyed intensively from 2000 to 2001. The researchers identified and differentiated between "sites" and "non-sites" in the ASTER images of the area. Thanks to the presence of anthrosols in what had once been inhabited areas, sites in the images had a different spectral signature than non-sites.

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Aldo Foe is an intern at ARCHAEOLOGY.