The Historical Archaeology of Military Sites: Method and Topic

Chapter Two: Some Recommendations and Applications

ChaptEr two Geophysics Some Recommendations and Applications william F. hanna introduCtion Historical archaeologists are well-schooled in the traditional methods of visual walkovers, shovel test pitting , trenching, and cutting sharply defined excavation units and using rake, hoe, brush, screen, and trowel. While these traditional methods remain important, tools for remotely sensing the presence and placement of subsurface objects and structural features can greatly reduce the time required to plan and expedite an excavation. Some archaeologists broadly include the bulbous-tipped steel probe (Richardson 2002) and the spoon-tipped soil auger as tools of remote sensing. Such minimally invasive probing involves sensing, by feel and sound, mechanical resistance or vibrations that indicate soil compactness and the presence of soil disturbance. Among all remote sensing tools available, geophysical tools are the least invasive and are the most efficient in terms of saving time. The purpose of this chapter is to comment on a few geophysical tools and techniques recommended for shallow terrestrial archaeology, to provide brief examples of historical projects in which we have used these tools, and to summarize a few conclusions, specifically about soldier gravesites, a principal focus of our work. Because we refer to specific sites later, some of the sites in northern Virginia and adjacent areas, mostly associated with the Civil War, where we have conducted geophysical work are shown in fig. 2.1. maps, photoGraphs, imaGEs, and CoordinatEs The geophysical toolbox initially includes maps and aerial photographs (Wilson 2000), many of which can be downloaded at no cost from the Internet, and remote-sensing images (Sever 2000), which can be purchased through the website of the Earth Resources Observation and Science (EROS) Data Center of the U.S. Geological Survey. Field coordinates can be established using combinations of compass, measurement tapes, theodolite, electric distance measurement device (the last two embodied within a single “total station”), or differential Global Positioning System FiGurE 2.1. Map showing archaeogeophysical sites, mostly centered in northern Virginia and connected to the Civil War. 12 william f. hanna (GPS) device updated via radio signals (Weymouth and Huggins 1985). Positioning coordinates from the air is possible, but expensive, using gyroscopically-stabilized accelerometers, updated by laser tracking and ranging, and integrated with a laser altimeter (Brown et al. 1987). The datum and baseline of the survey should be marked as permanently as possible with iron spikes, or other identifiers that can be recovered later using a magnetic locator or metal detector. For small areas of an acre or less, we usually lay out a grid of as many as fifty parallel 100-ft measurement tapes for mapping above-ground features and for defining transects along which we can drag a groundpenetrating radar (GPR) antenna without disrupting the tapes. The tapes are then photographed from high above, offering, when zoomed, a detailed, point-bypoint picture of our grid for future use. GEophysiCal tools For arChaEoloGy at military sitEs Nearly a hundred geophysical tools and techniques are available to archaeologists working at shallow depths in military settings. They can be classified by (1) whether they are “active” (involving manmade signals ) or “passive” (involving natural signals); (2) sensor location (e.g., spaceborne, airborne, terrestrial-surface, subsurface [borehole or cave], water-surface, or subaqueous ); and (3) physics involved (e.g., gravity, magnetic , geo-electric, electromagnetic induction, seismic, sonic, radar, thermal, and radioactivity). A complete list, with its attendant jargon and acronyms, is almost overwhelming to workers outside mainstream geophysics , physics, hydrology, or engineering, thus no attempt is made to offer a comprehensive list here. A prodigious amount of information about these techniques, including those most suited to archaeogeophysics , can be obtained from journal articles, books, applet applications, and Internet sites of companies, universities, and government agencies. One exceptionally informative, extensive, in-depth, graphics-rich, website is maintained by Professor Kevin L. Kvamme, who heads the University of Arkansas Archeo-Imaging Laboratory and who also supports a North American Database of Archaeological Geophysics. Special attention is called to the National Park Service (NPS) workshops on archaeological prospecting techniques, coordinated annually by Steven L. De Vore. Recommended textbooks on shallow geophysical techniques include, but are not restricted to: Parasnis (1996), Reynolds (1997), Sharma (1997), Telford, Geldart, and Sheriff (2003), Burger, Sheehan , and Jones (2006), and Stefano and Piro (2009). The last of these is especially designed for student computer interaction. Recommended textbooks on archaeogeophysics include, but are not restricted to, Aitkin (1974), Scollar et al. (1990), Bevan (1998), Clark (2000), Williamson and Nickens (2000), Kvamme (2001, 2005), Gafney and Gater (2003...