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Kinds of Geophysical Surveys We Perform (click on the instrument type for details on what each instrument can do and find)
- Magnetic Gradient, Instrument: Geoscan Research
FM 256 Fluxgate
Gradiometer
- Electrical Resistance/Resistivity, Instrument: Geoscan Research
RM 15
Electrical Resistance Meter
- Ground Penetrating Radar (GPR), Instrument: Sensors and Software Noggin Smartcart 500
- Metal Detector, Instrument: Minelab Quattro MP; Fischer 1225-X
- Magnetic Susceptibility, Instrument: Bartington MS2 with MS2B lab sensor
One of the key archaeological site attributes used in Ohio to determine if a site is eligible or potentially eligible for the National Register of Historic Places (NRHP) is the presence, or potential presence, of subsurface archaeological features. Most archaeological firms search for these intact archaeological remains by removing the plowzone layer with heavy equipment (including backhoes, earthmovers, bulldozers, trackhoes, etc.), and in the process they destroy much of the archaeological site and discard potentially important artifacts and artifact patterning present in the plowzone. Ironically, most projects that employ heavy machinery to strip off the plowzone of small areas fail to even find archaeological features, even if many are present. OVAC archaeologists use geophysical surveys to pinpoint buried archaeological resources before beginning our excavations, which are typically done by hand. Our combination of geophysical survey and strategically placed hand excavation units has many benefits, both in terms of cost and site preservation:
- Cost and time effective: geophysical surveys allow us to map the subsurface properties of entire sites, not just small machine-excavated blocks. Typical surveys can be completed in about a day or two. The results can then be used to target specific features, rather than blindly excavating for them using heavy equipment.
- Failure to identify buried cultural features is minimized: The use of heavy machinery on archaeological sites is expensive, time consuming, destructive, and sometimes difficult to organize since it can be difficult to find experienced operators who are available. On Phase II-level site assessment projects, the use of heavy machinery commonly fails to yield any buried archaeological remains because of limitations (mostly due to cost) in the size of area that can be excavated. If, after the expense and hassle of setting up and conducting a heavy machinery excavation, the heavy machinery work does not uncover intact archaeological remains, even though they are present on the site, the use of the heavy machinery was a complete failure. We guard against failed excavations by identifying the buried cultural resources before beginning the excavation.
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