High-Resolution Geophysics

Geophysical investigations can provide valuable information for immediate and future goals for an archaeological project.  The information can be used in two different ways.  First, it can be integrated with other site data (e.g. historic maps, current excavation maps) to provide a site-wide context for a better understanding of site layout and boundaries.  Second, it provides a basis for making decisions about immediate targets for investigation and longer-term planning, preservation, and protection of the site as a whole.

The geophysical data do not tell a story that is independent from the rest of the site data and it is essential that the geophysical group interact on a regular basis with the rest of a research team.  Geophysical data images typically present a two dimensional representation of a complex sequence of archaeological events and natural conditions.  While the geophysicists may perceive these images in one way, specialists with a very different view of the site may perceive them in other ways that enrich and expand the geophysicists' interpretation.  Likewise, interaction of the geophysicists with archaeologists during and after excavation will provide the geophysicists with a better understanding of what particular geophysical responses may mean - and allow the archaeologists to develop a 'gestalt' that will allow them to better comprehend and incorporate geophysical information into their thinking.  This type of interaction between geophysics and archaeology is not common and can be challenging to implement.  However, it can facilitate a more vibrant interpretation of the geophysics and the site itself than the geophysical team alone can provide.

Examples of geophysical investigations can be found in Previous Projects or Publications.

Commonly Applied Techniques

 DC Resistivity - This method maps electrical variations in the ground.  Traditional archaeological application of this method has been to map lateral changes in shallow resistance, but recent advances in computer processing have allowed for the possibility of mapping the variations of electrical properties as 2D profiles, or in 3D.

Electromagnetic (EM) methods – EM methods offer the possibility to rapidly measure variations of soil electrical properties, as well as to delineate the distribution of metallic objects.  EM measurements are commonly applied to industrial investigations with the goal of locating underground tanks or pipes, but certain types of equipment are effective in mapping changes in shallow soil properties.

Ground Penetrating Radar (GPR) - GPR offers the highest resolution of any geophysical method, but only when soil conditions are favorable. Typical applications we have conducted with this technique have included the mapping of graves, middens, buried foundations, as well as industrial targets. 

Magnetics – Magnetic Surveys offer the best combination of resolution and speed of mapping.  We routinely conduct total field and gradiometer surveys to map the distribution of a wide range of buried materials.  The sensitivity of this method allows for its application in mapping subtle changes in soil conditions for archaeological projects.

The use of multiple geophysical instruments and methods at any given site will often produce more comprehensible results than relying on a single method or approach.  Sites vary dramatically in their cultural and physical properties and it is difficult to know in advance which methods will be useful and which will not.  Testing a variety of instruments at a site should be an integral part of an overall survey design.  For example, a combination of magnetics and DC resistivity is often effective as a means to map the limits of cultural resources in advance of excavating.  Targets associated with metal are often best delineated with an EM method along with magnetics.  Soil layering is frequently best delineated with GPR together with DC resistivity.

Each project has site-specific conditions that are different so selection of the most appropriate geophysical methods should be made with consultation between the archaeologist and geophysicist.

Equipment

We own the following geophysical equipment: