Key Words: Ground Penetrating Radar, Clandestine Burials, Geophysical Applications in Anthropology, Historic Cemeteries introduction and purpose
Download 0.69 Mb. View original pdf
|
- Navigate this page:
- Table 2
| Figure 1. A reflection profile showing GPR data collected in D along a single transect. Note the two readily apparent downward facing hyperbolas which are representative of anomalies. Electromagnetic waves are defined by their wavelength which is, in turn, determined by the oscillating force producing them. This frequency is measured in units of hertz (Leckebusch, 2003; Conyers, 2004). Most GPR units operate with frequencies ranging from 10 to 1500 megahertz which is within the frequency band of many common communication devices. These can possibly cause interference during data collection and should be accounted for in post- processing of data (Schultz, 2003; Conyers, 2004). One of the most important aspects fora GPR survey is the selection of the antenna which depends largely on two variables depth required and resolution needed (Table 2). An increase in antenna frequency provides greater resolution but a decrease in depth of wave propagation. Conversely, a decrease in antenna frequency provides less resolution but an increase in depth of wave propagation (Tischler, 2003; Conyers, 2004; Schultz and Martin, 2011; Conyers, 2012). Determination of the required antenna frequency is tied to the estimation of the relative dielectric permittivity (RDP) of the subsurface media at a site. The RDP measures the capability of propagated electromagnetic waves to travel through a given medium and the likelihood of either a signal return or attenuation. For most archaeological investigations this is synonymous with the velocity of the propagated radar pulse, a factor used to determine relative depth. Radar energy will move slower through material with a high RDP and conversely radar energy will move faster through material with a low RDP (Smith and Jol, 1995; Schultz, 2003, Tischler, 2003; Conyers 2004; Conyers 2012). Table 2. Relative depth of penetration and resolution of various antennas, based on a scale of 1 to 10, adapted from (Tischler, 2003). Download 0.69 Mb. Share with your friends:
|