Key Words: Ground Penetrating Radar, Clandestine Burials, Geophysical Applications in Anthropology, Historic Cemeteries introduction and purpose
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- Survey Survey type Average Depth Antenna Frequency
| Antenna Frequency Depth Resolution 100 MHz 10 1 200 MHz 9 2 300 MHz 8 3 400 MHz 7 4 500 MHz 6 5 600 MHz 5 6 700 MHz 4 7 800 MHz 3 8 900 MHz 2 9 1000 MHz 1 10 Once site factors are taken into account it is possible to choose with relative surety the best antenna frequency to operate at a site. Generally, many of the antenna frequencies available on the market are impractical for use in archeological or forensic investigations. Very high and very low frequencies provide either too much resolution and not enough depth, as in the former, or too much depth with too little resolution, as in the latter. For the purposes of current archaeological or forensic investigations an antenna frequency range of between 200 MHz and 500 MHz is sufficient for most surveys (Table 3). Table 3. A selection of GPR surveys from within the last ten years showing a variety of site survey types and the range of antennas used. Most archaeological or forensic surveys are conducted with antennas falling between 200-500 MHz. Survey Survey type Average Depth Antenna Frequency Teixidó et al., 2014 Monumental Platform Spain) 2 meters 400 MHz Ruffell et al., 2009 Historic Graves Ireland) 2 meters 200 MHz Doolittle and Bellatoni, 2010 Historic Graves (United States) 2 meters 400 MHz Sarris et al., 2007 Ancient Graves Greece) 2 meters 225 MHz and 450 MHz Shaaban et al., 2007 Ancient Graves (Egypt) Up to 8 meters, most at 4 meters 200 MHz Schultz and Martin, 2012 Forensic proxy burial United States) 0.5 to 1 meter 250 MHz and 500 MHz While one benefit of GPR surveys is an immediate infield estimation of anomalies, post processing of reflection profiles is still necessary. Much of this processing is dedicated to reducing background noise in reflection profiles that may have been caused by devices operating at or near the antenna frequency in the area or, as is more often the case, to de-emphasize known noise-causing agents such as tree roots or animal burrows. As much of the hardware and software produced for GPR is focused more on industrial or geological prospection, processing can be a difficult and time consuming process. Considerable effort has been put into researching best practices for the application of these processing steps to archaeological sites, but there is no one way to process raw data and indeed much of the processing is determined by the site, soil profiles, and even the weather at varying times of the year (Leckebusch, 2003, Conyers, 2004; Conyers and Leckebusch, 2010; Conyers, 2012). Conyers (2004) suggests three basic post- processing steps that should happen in all cases 1) prior to all other processing steps the profile should be corrected spatially for horizontal and vertical dimensions 2) background removal, a noise filtering process and 3) range gaining to enhance important reflections. As each site and survey is unique, post processing steps beyond these basics may change, but once a system of processing is established fora site it is recommended to maintain that processing order. One of the latest advancements to aid in GPR surveys is the introduction of D imaging software (Leckebusch, 2003; Doolittle and Bellatoni, 2010; Conyers, 2012). By collecting data on both the x and they axes of a survey grid, this software can digitally interpolate information fora D image of anomalies encountered during a survey. This software also provides the ability to produce amplitude slice maps that allow fora better estimation of size and depth of subsurface cultural features (Figure 2). This software has proven to be a boon to GPR research both in archaeological settings (Conyers and Leckebusch, 2010) and for forensic investigations Schultz, 2006; Schultz, 2010). Download 0.69 Mb. Share with your friends:
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