Once a cultural or archeological resource site is identified it then must be assessed in order to determine its significance. The costs associated with the National Register of Historic Places (NRHP) phase II eligibility assessment of cultural and archeological resources are quite high.
The objective of this work was to develop a method using acoustics to assess sites more cost effectively by avoiding the usual detailed excavation.
Acoustic sound waves can non-destructively transmit into and through the ground. These waves can be used to probe beneath the surface by reflecting off of media of higher relative density (i.e., bone, ceramic, stone, and glass) than the surrounding medium and then be detected. The main thrust of this effort was to develop a system using a phased array of ultrasonic/acoustic transducer’s that can image sub-surface features of differing densities accurately. By varying each transducers time delay and input amplitude, the focused ultrasonic/acoustic probe can be steered to examine successive control volumes beneath the surface. Reflected signals then are detected and, through computer imaging and enhancement, the location of possible artifacts can be identified while also gaining information about their shape and dimension. The predictive capabilities are compared to actual archeological findings under varying conditions in order to determine reliability. The main challenges of this work were in the areas of signal attenuation and signal processing/analysis.
Through this effort, the following were accomplished: a computer-controlled movement system was designed, targets for the quantitative assessment of imaging ability/resolution were selected, and computer algorithms for the various approaches to signal processing were prepared for use with the acoustic data. This project was completed in FY 1997.
The main benefit of this research was to be able to non-destructively probe beneath the earth's surface to assess possible buried artifacts at a fraction of the cost associated with excavation. This will allow for the more efficient use of limited excavation resources and will aid in speeding the overall site assessment. In the Army alone, there are approximately 120,000 archeological sites, of which only 10 percent have been assessed and the site significance determined. A phase II eligibility assessment for the NRHP typically costs between $10K and $30K per site. This method also will be useful in achieving compliance with the requirements stated in the Native American Grave Protection and Repatriation Act. An additional benefit would be the rapid assessment capability employed on construction sites when an unanticipated discovery of a site occurs thus avoiding both delays and damaging artifacts.