Ground Penetrating Radar

The Flinders University Archaeology Department ran a masterclass a little while back on Ground Penetrating Radar (GPR) presented by Prof. Larry Conyers. I signed up for this course because I like the idea of being able to see below the earth’s surface without having to dig, that as archaeologists we are getting to the point of being able to examine some aspects of a site without destroying it in the process.

So when we are looking at GPR data, what are we actually looking at?
* the path of an electromagnetic wave as it passes through the earth.
* reflections: the waves are transmitted, hit something, partially bounce back and are collected by the receiver.
* porosity and permeability of the earth – water can both help and hinder the transmission of the waves. In some cases, water is trapped underground by substances such as wood so they show up better. In other cases, water might flow between cobblestones or pavers to create very differentiated results, or alternatively it does not flow under asphalt, so the stratigraphy below is both slower to change and more intact.
* dislocations in stratigraphy – bones might not show up, but perhaps the edges of the grave will.
* history of the environment, for example old river channels that became lakes, or old ocean floors, old field furrows. The history of the environment is important information to archaeologists; environment in many ways dictates activity.

The first day was all theory – an introduction to different aspects of the science, maths and software involved. On the second day we headed up into the hills to an old graveyard to survey. A couple of the participants brought their own GPRs with them and we spent a large part of the cold, rainy day collecting data on top of a windswept hill, dodging the odd patch of hail.

The third day (sunny of course) was back in the lab looking at what we had collected, trying out different angles and piecing things together. It was a great intro to a very complex survey method. I’m interested to see more applications.

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