The archaeological site of Petra is noted for its impressive monumental architecture and rock-cut facades. An open portion of the site (termed the `Lower Market'), located at the heart of Petra's city centre just east of the `Great Temple', was tested with ground-penetrating radar (GPR). The purpose of this survey was to locate buried architecture as a guide for the placement of excavations.
Although there were few surface indications of buried architecture in this area, its central location suggested the area might be somehow related to the ceremonial, economic or political activities of the city. Previous excavations near by discovered an open-air pool with an island-pavilion at its centre (Bedal 2000). These findings indicated that the `Lower Market' area was likely a formal garden.
In July 2001 GPR mapping of the northern portion of the Lower Market was begun, using a GSSI (Geophysical Survey Systems Inc.) SIR-2000 radar system. A 400-MHz dual antenna was used to collect GPR reflection data over two grids with a maximum extent of 68x51 m (FIGURE 1).
[FIGURE 1 OMITTED]
Ground-penetrating radar is a geophysical method that can map the spatial extent of buried objects and archaeological features in three dimensions. Radar waves are propagated in pulses from a surface antenna, reflected off buried objects, features, bedding contacts or soil units, and detected back at a surface receiving antenna (Conyers & Goodman 1997). Any contrast in buried materials will produce a reflected wave whose amplitude is a function of the difference in physical or chemical properties.
When the travel times of radar pulses are measured, and their velocity through the ground is known, depth in the ground can be accurately measured (Conyers & Lucius 1996). In the GPR method, radar antennae are moved along the ground in transects producing many two-dimensional profiles of subsurface stratigraphy and buried features. When the reflections are correlated and processed within a grid of data, an accurate three-dimensional picture of buried features and associated stratigraphy can be constructed. Horizontal slice-maps of the highest amplitude reflections produce images of buried architecture while areas of low amplitude denote little reflection and therefore …