Key Words: Ground Penetrating Radar, Clandestine Burials, Geophysical Applications in Anthropology, Historic Cemeteries introduction and purpose
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| GPR HISTORY Ground Penetrating Radar, as we know it today, has its inception in the radar technology developed during WWII and was used largely for the detection of aircraft. As Conyers (2004) notes, this technology was reevaluated in the s as US. Air Force radar technicians noticed that radar pulses penetrated glacial ice when flying over Greenland, suggesting its use for subsurface prospection. An early GPR system was developed for use by NASA in 1972 and was dispatched with the Apollo 17 mission in order to better understand the geology of the moon (Conyers, 2006). The s saw the growth of GPR as a geotechnical tool when researchers in the fields of geophysics, geology and physics began to incorporate GPR into their investigations (Leckebusch, 2003; Conyers, 2004; Conyers and Leckebusch, 2010). The field of archaeology was quick to adapt GPR to site surveying with some initial, albeit slow success. Early GPR units provided little in the way of immediate readability and data storage for example, in some models oscilloscopes provided a signal readout which had to be photographed in order to be stored (Leckebusch, 2003). However, in 1975 one of the first GPR applications to an archaeological investigation was conducted at Chaco Canyon, New Mexico. Vickers and Dolphin (1975) demonstrated the utility of GPR for identifying anomalies at about m below surface. These anomalies, when ground-truthed, were found to be mud brick walls. Early utilization of GPR in the field offered little more than the location of anomalies in the subsurface which were often hard to distinguish between anthropogenic or archaeological features and that of naturally occurring soil change (Leckebusch, 2003; Conyers 2004; Conyers Succeeding decades saw a refinement of GPR use within archaeology as researchers focused on the functionality of this tool in a variety of conditions and locales (Sheets, 1985; Imai et al., 1987; Goodman and Nishimura 1993; Conyers, 2004). Certainly a great impetus to the increased use of GPR in archaeological surveys can be attributed to advancement of digital technology over the last several decades which allowed for the manufacture of GPR components providing real-time data displays as well as digital data collection (Leckebusch 2003; Conyers 2004). Advancements continue to be made in GPR processing and visualization, driven largely by its increasing acceptance in the field of archaeology and especially due to its utilization in cultural resource management (CRM) firms who take advantage of its relatively low cost (Table 1) and data collection speed (Grasmueck et al., 2004; Johnson and Haley, 2006; Lockhart and Green, 2006; Conyers and Leckebusch, 2010; Conyers, 2012). Present research in GPR continues to focus on the advancement of processing techniques and the testing of GPR in areas previously deemed unlikely to produce valid results (Leckebusch, 2003; Schultz, 2008; Schultz et al, 2006; Schultz and Martin, 2011; Lualdi and Lombardi, 2014; Teixidó et al., 2014). The ability to render subsurface data collected with GPR in D models, while not new, continues to be a focal point of archaeological and forensic investigations as digital processing technology advances. Increasingly, data collected by GPR can be readily integrated into various other mapping and visualization software packages that provide access to global positioning systems (GPS) information of the site and accurate subsurface D models of anomalies that can be transferred into geographic information systems (GIS). These applications allow fora noninvasive manner in which to effectively study sites as well as a method of long-term digital preservation (Lualdi and Lombardi, 2014; Teixidó et al., 2014; Catapano, et al., 2014). Table 1. One of the driving forces for the inclusion of GPR in archaeological investigations is its cost effectiveness. In the table below a hypothetical cultural resource management survey is outlined. The top portion of the table shows the cost of the survey using remote sensing equipment and compares this to the cost of a traditional survey below it. As can be seen, remote sensing surveys are far more cost effective than traditional, invasive surveys (Johnson and Haley, 2006). |