14/12/2013 by All Things AAFS!

Quick Tips: Archaeological Techniques – Ground Penetrating Radar.

Ground-penetrating or probing radar (GPR) is a non-destructive, geophysical method that uses radar pulses to image the subsurface. The principles of ground-penetrating radar are similar to reflection seismology, except that electromagnetic energy is used instead of acoustic energy, and reflections appear at boundaries with different dielectric constants instead of acoustic impedances.

Ground-penetrating radar was applied in the 1940’s after the use of radar to detect enemy aircraft’s during WW2. In 1960’s, due to the progression of this surveying technique, it was primarily used to probe and explore the polar ice. By using GPR in relation to these two applications, a P-38 lightening fighter plane was pinpointed within the ice surrounding Greenland in 1992. The P-38 was originally part of a squadron of six fighters and two B17 Flying Fortresses that ditched just over Greenland in 1942. The P-38 fighter plane was later recovered from a depth of 75m.

How does Ground-penetrating radar work?

GPR works by emitting high frequency, usually polarized, radio waves via antennas, into the ground. If the area being surveyed contains artefacts or hidden archaeology; these electromagnetic waves are reflected back. When the wave hits a buried object or a boundary with different di-electric constants, the receiving antenna records the variations in the reflected return signal. These returned signals are then collected and interpreted to identify any hidden archaeology within the surveyed area.

N.B. Higher frequencies do not penetrate the ground as far as lower frequencies do, but these higher frequencies give a better resolution. Also the radar emitting antennas are usually in contact with the ground for the strongest signal strength; however, GPR air launched antennas can be used above the ground.

Advantages of Ground-penetrating Radar:

GPR is non-destructive and not invasive – helping to preserve the archaeology/landscape.
GPR can be used in a variety of media/sediments including; rock, soil, ice, fresh water, pavements and structures.
It can detect objects, changes in material, and voids/cracks in the ground.

Disadvantages of Ground-penetrating Radar:

The depth range of GPR is limited by the electrical conductivity of the ground. As conductivity increases, the penetration depth decreases. This is because the electromagnetic energy is more quickly dissipated into heat, causing a loss in signal strength at depth.
In moist and/or clay-laden soils and soils with high electrical conductivity, penetration is sometimes only a few centimetres.
Metal can interfere with the electromagnetic radiation – this can give false results.

References:

Balme, J., Paterson, A. 2006. Archaeology in Practice: A Student Guide to Archaeological Analayses. Oxford, UK: Blackwell Publishing. Pg 218.

Renfrew, C., Bahn, P. 1991. Archaeology: Theories, Methods and Practice. London, UK: Thames & Hudson. Pg 249-53.

Click here to read more Quick Tip posts!

18/07/2013 by All Things AAFS!

New Evidence Supports Conflict is Not Innate.

In a previous post – which can be found by clicking here – I had examined whether conflict was innate for humans after a lecture in University, which I concluded was true by analysing different theories but stressed that conflict only becomes active due to a stimulus. That stimulus could either be biological, seen in aggressive mating, or environmental, such as intraspecific/intrespecific competition. But a recent study, noticed by the BBC has put a spanner in the works, as the leading researcher – Patrik Soderberg – says that conflict isn’t actually innate.

Soderberg’s research based its findings by studying isolated tribes from numerous places around the world which had been studied over the last century. By using modern primitive isolated tribes they were able to have a sample which was cut off from the modern day life and utilising the wild plants and animals that inhibit their environment, surviving like the much older hunter-gatherers.

Ancient hunter-gatherer cave art.

Using these modern day tribes as an analogy for the earlier societies that ruled the lands, they assessed and analysed any violent deaths. They found that in their sample populations there were 148 violent deaths, but very few were caused by widespread war. Most of the violent deaths were caused by personal motives ranging from family feuds or adultery.

Soderberg has admitted that these modern tribes were not a ‘perfect model’ for the ancient civilisations but said that due to vast significant similarities they did allow for an insight into the past. From this study he concluded that war may have developed later as the hunter gathers became more agriculture orientated and territorial with a complex social structure. “As humans settled down, then war becomes more dominant and present. For these primitive societies, war has not yet entered the picture,”.

References:

BBC. 2013. Primitive human society ‘not driven by war’. BBC News. Available here.

Soderberg, P., Fry, D. 2013. Latest Skirmish Over Ancestral Violence Strikes Blow for Peace. Science. 341, 6143. P224. Here is a link to view the .pdf of this very interesting article.