Today's radiometric thermal cameras, coupled with small, inexpensive drones controlled by a smartphone or tablet, have made aerial thermography more accurate, comprehensive and accessible for archaeologists. Multiple aerial images can now be mapped together using photogrammetric software to automatically align images, and sofware with ortho-image capabilities can be used to make the scale of the images uniform. A Chaco-era room block (LA 170609) at Blue J, N.M., as it appears in (a) 5:18 a.m. thermal image; (b) architectural plan produced by test excavations; (c) a color image, and thermal images from (d) 6:18 a.m.; (e) 7:18 a.m.; and (f) 9:58 p.m. Courtesy of Jesse Casana, John Kantner, Adam Wiewel and Jackson Cothren. To demonstrate the effectiveness of aerial thermal surveys, researchers from Dartmouth College conducted case studies at six archaeological sites in North America, the Mediterranean and the Middle East. They analyzed how variables like weather, environment, time of day, ground cover and archaeological features could impact the results of aerial thermography, and compared their findings to earlier research and historical images. Based on their work, the researchers developed a guide for archaeologists on how to use aerial thermography to explore archaeological sites more thoroughly and expeditiously. The guide illustrates cases in which aerial thermography is effective, as well as contexts in which the vegetation cover, soil composition or depth, and specific features of the site make it more challenging to use. “A lot of what we’ve learned from our research to date shows how much local environmental conditions and the timing of surveys can impact how well thermal imagery will reveal archaeological remains. Yet, the more we understand these issues, the better we are able to deploy the technology,” said professor Jesse Casana. For example, new technology has become available to filter the noise caused by vegetation. Visibility of archaeological features can be improved using thermal radiometric images. At one site, an ancestral Pueblo settlement in Blue J, N.M., researchers were able to map detailed architectural plans of a dozen ancient house compounds — a discovery enabled by the site’s conditions, including the soil matrix and low density ground cover, at the time of the aerial thermography. The team was also able to map previously undocumented architectural features using aerial surveys. According to the researchers, their methodology produces data of a quality comparable to traditional archaeological geophysics in terms of feature visibility. Aerial thermography has the advantage of allowing data to be collected very rapidly, over large areas, with minimal cost and processing requirements. “I think our results demonstrate aerial thermography’s potential to transform how we explore archaeological landscapes in many parts of the world,” said Casana, who has been using aerial thermography for five years in his research. The research was published in Advances in Archaeological Practice (doi: 10.1017/aap.2017.23) and Science Direct (doi:10.1016/j.jas.2014.02.015).