Petra Upper MarketGPR showing structurePetra Excavation
 

Abstract and Notes


 

 

Ground-Penetrating Radar (GPR) Mapping as a method for planning excavation strategies, Petra, Jordan

 


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Introduction: Finding and Mapping Deeply Buried Archaeological Features

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Archaeologists have long puzzled over strategies for locating and mapping buriedarchaeological features.  Often field researchers have relied on coring, auguring, and shovel testing, which are random search methods at best.  Geophysical methods such as magnetometers, resistivity and electro-magnetic conductivity can produce maps of buried features, but ground-penetrating radar (GPR) is the only technique that can make maps in three-dimensions. 

View Full Text Ground-penetrating radar (GPR) is a three-dimensional mapping technique. 

  • GPR creates pulses of radar energy at a surface antenna and projects them into the ground.   As the transmitted radar waves encounter chemical or physical changes in the ground, energy is reflected back to the surface and recorded at the antenna.  

  • When the antennas are pulled across the ground in transects, a series of subsurface reflections are recorded.
    Figure 1
    Figure 1: Pulling Antenna

  • All reflections are then plotted in a two-dimensional profile.  When radar travel times are converted to depth, the GPR images can reveal some of the buried features and stratigraphic layers that are usually exposed during excavation.
    Figure 2
    Figure 2: Example of a GPR reflection profile
  • Three-dimensional GPR data are obtained by collecting many transects within a grid.  When transects are spaced closely together and the reflections from all the transects are analyzed spatially, they produce a three-dimensional "cube" of the data.
    Figure 3
    Figure 3: How profiles make up a 3D cube

View Full Text Since GPR maps can be produced immediately after data acquisition, they can be used to plan excavations without delay.

  • Maps are typically produced in horizontal slices showing the presence of buried archaeological features across a site.  They are similar to arbitrary level-maps in standard archaeological investigations, except they are showing the strength of radar reflections within certain depth intervals.
    Figure 4
    Figure 4: Slice Maps of Buried Architecture  
  • Subsurface testing can be planned from the GPR slice maps, allowing for a non-random testing strategy where the location and depth of most of the buried features is known in advance.
  • During and after test excavations GPR maps and profiles can be calibrated by correlating the GPR reflections to excavation data.
  • When limited excavation information is used to further interpret the GPR maps, the un-excavated portions of the site can be characterized.

View Full TextPetra was used as a test site for the integration of GPR and excavation data. 

Figure 5
Figure 5: Base Map

  • A flat area 88 x 51 meters was surveyed, called the "Lower Market", where little was known about the subsurface, and there were no surface indications of buried features.

Figure 6
Figure 6: Lower Market Area viewed from the south

  • GPR maps were used as a guide to excavations, and information from those subsurface tests was used to evaluate the technique's accuracy.



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______________________________________________________________________
Copyright © 2002. All rights reserved.
Lawrence B. Conyers, University of Denver · lconyers@du.edu · 303.871.2684
Eileen G. Ernenwein, University of Arkansas · eernenw@uark.edu
Leigh-Ann Bedal, University of New York, Erie · lbedal@yahoo.com