Ground-Penetrating Radar

Ground-penetrating radar (GPR) has recently gained a wide acceptance in the archaeological community as a method that can quickly and accurately locate buried archaeological features, artifacts, and important cultural strata in the near-surface. The GPR method has been especially effective in certain sediments and soils between about 20 cm and 5 m below the ground surface, where the targets to be imaged are fairly large, hollow, or linear or have significant physical and chemical properties that contrast with the surrounding medium. Features as diverse as Mayan house platforms and plazas been discovered and mapped using the method. The archaeological community has also recently seen the need for near-surface mapping using GPR in order to identify buried cultural remains for protection and future preservation and as a planning tool for selective excavation. Ground-penetrating radar has a reputation as one of the more complex of archaeological geophysical methods because it collects large amounts of reflection data from numerous transects within grids, oftentimes producing massive three-dimensional databases. The ability to detect multiple interfaces at different depths below the surface, the interpretation of these numerous reflections, and the difficulty in correlating the abundance of reflections between many profiles within a grid can make GPR data collection and processing a somewhat intimidating venture for the uninitiated. However, 132 ~ Lawrence B. Conyers with modern data acquisition and processing and a knowledge of how radar energy travels and reflects from interfaces in the ground, GPR mapping in archaeology need not be as daunting as its reputation suggests. Some of the earliest model GPR systems recorded raw subsurface reflection data on paper printouts that allowed little postacquisition processing. Although these radar systems, a few of which are still in use, can many times yield valuable subsurface information, modern digital systems record reflection data on a computer hard drive for later filtering, processing, and sophisticated data analysis. Most important, when the data are digital, a computer can process, filter, and enhance raw field data almost immediately after they are collected. Computer manipulation of the digital data, which removes unwanted noise and enhances the portions of the signal that are important, allows for rapid data processing and dramatically increases subsurface resolution and interpretation of complex data sets. Accompanied by a trend in equipment miniaturization, computer processing of the acquired GPR data can now occur immediately after they are acquired and interpretation can often begin while the operators are still …