Archaeological Survey

Geophysical Survey

Geophysical survey or archaeological prospection is a noninvasive method for aiding in identification of cultural activity within the subsurface. Often, there is little to no evidence of cultural features (i.e., structures, hearths, storage/refuse pits, cellars, foundations, graves) or materials above ground that can provide the most accurate information about specific site layout or site integrity, especially in prehistoric contexts. Other factors, such as agriculture, ground cover, erosion, flooding, or earth moving activities prevent or interfere with the detection of cultural materials and features. Consequently, the use of remote sensing equipment provides, in various ways, an opportunity to “glance” beneath the soil prior to excavation.

IPFW-AS personnel using geophyical equipment

Large scale, low resolution survey is commonly used to generate information about large site areas at a much lower cost (in time and money) than traditional archaeological excavation.  Higher resolution data collection is often employed to investigate smaller areas of sites and even individual features. The relatively low cost and high speed of geophysical survey, as well as its non-invasive, non-destructive nature, often makes geophysics an attractive complement or alternative to excavation. When appropriate, geophysical surveys can save substantial amounts of time and labor during all phases of archaeological investigation.

The application of geophysics to archaeology rests on the fact that many of the activities carried out by humans on an archaeological site produce changes in the physical or chemical properties of the soil and/or its contents.  The magnetic and electrical properties of the soil may be altered by heating, for example, compaction, or the inclusion of materials with different properties (such as when a pit is excavated and subsequently refilled with a different kind of sediment). Geophysical instruments are used to make and record measurements of the properties of the soil at or near the ground surface. If the localized alterations contrast sufficiently with the surrounding matrix (areas that have not been altered), they can be detected as geophysical anomalies.  The properties of these anomalies (size, shape, contrast, depth, etc.) may allow some inference to be made about the feature that is producing the anomaly.  Interpretation can be aided by the use of multiple instruments and knowledge of the properties of the natural sediments in the area.

The IPFW-AS had multiple equipment, resources, and experience with geophysical prospection techniques that could have been used for all phases of cultural resource management and research projects throughout the Midwest. They also could have provided student/client training by their skilled and dedicated staff. Their laboratory owned and operated a ground penetrating radar (GSSI TerraSIRch SIR System 3000) with shielded 200 and 400 MHz antennas, two magnetic gradiometers (Bartington Grad 601-2, Geoscan FM-256), an electrical resistivity meter (Geoscan Research RM 15 with a MPX-15 multiplexer), and a multi-frequency EM conductivity meter (GSSI Profiler EMP-400). They maintained a constantly updated suite of software packages including ArcheoSurveyor II and GPR SLICE v7.0, for rapid and accurate analyses of both two and three dimensional subsurface topology.