Archive for the ‘geophysics’ category

Somewhere after the party/ early life crisis

September 8, 2008

I submitted my thesis last Monday and my body is slowly coming to terms with the cessation of the partying. Now I find myself asking the same question that my personified liver would pose, now what?!  It seems that this question is just the tip of the iceberg; some of my Scandinavian friends call this the beginning of the ‘early life crisis’. My parents noted that this would be the first time I am not going back to school in almost 20 years.

Sweet jesus, now I have to get a job. Sadly, it seems that the “credit crunch” has significantly effected development (or at least new jobs in the archaeology sector) in the UK so I will be returning to Canada. If I had EU status, it wouldn’t matter but given that I have to spend a hundred pounds just to stay on with a work visa I think its becoming too financially taxing. From the sounds of things the mythical “archaeology factory” is still running strong in Alberta, a Canadian province, economical, drunk with oil (they have more oil than Iraq does but please don’t tell our Yankee neighbors). Ok the “archaeology factory” is kind of an inside joke which mocks the job instability and unpredictable nature of professional archaeology.

I am now looking for, an archaeology-based, job until November.

If anyone is interested here is the abstract from my thesis.

This paper is composed of three sections. The first section will discuss the advantages of employing geophysics surveys on military sites followed by an assessment of the role geophysics fills within the context of other techniques employed by archaeologists. The second section will discuss the advantages of studying war graves and then will employ published geophysics surveys to assess the ability of the three most widely used geophysical techniques (resistivity, magnetics and ground-penetrating radar) to detect war graves. The third section will employ published geophysical surveys to provide examples of different features that can be detected on military and conflict sites from prehistoric times to the modern era.

If you are one of the hundred or so people around the world who is knee deep in geophysics and would like to learn more about my topic just ask and I can fire off a PDF copy of my dissertation. With feedback from the internal and external markers, I can polish that puppy up and perhaps publish it in one form or another.

Geophysics! With enough money, and insanity, you can do it at home!

July 8, 2008

Geophysics is like most TV archaeology programmes, the majority of the work is behind the scenes and unglamorous but important if any work is to be done. So how does one go about conducting a geophysical survey on an archaeological site?

What you’ll need
At least three people – one person to use the machine and collect the data and two “line monkeys” (and eventually one person needs to be able to use the software to view the results)
Many measuring tapes- preferably fiberglass and 60M long
Bamboo “canes”
At least 2 clotheslines with one meter intervals marked off with colored tape
Ranging rods (large metallic rods with alternating colors)
A geophysics recording device- resistivity or magnetic device depending on what you are looking for (Geoscan and Bartington are the two largest producers)
Interpretation software- geoscan seems to have the most widely used software
The right conditions- preferably flat, well drained and non magnetic soil with no brambles or flesh craving insect to be found

How do you get started?
A major concept to get your head around is the idea of a “baseline”. No, I’m not talking about the mating call of middle-class guys that you can hear before you even see their Jeep TJ or their Honda Civic. A baseline is a centerline that acts as the backbone for your survey. If you are doing a larger scale “landscape survey” then you would have a very long baseline which would be in the center of your area of interest, say a Rome fort. You are using this line to divide the landscape into smaller grids of 20 x 20M or 10 x 10M.

From this centerline you measure, or subdivided the line into, 20M intervals (or 10M ) and the triangulate the other two points. Yes that’s right, you have to use math in archaeology. Kids, remember to learn trigonometry and geometry. You have the length of two known points, how do you learn the unknown point(s)? Help me Pythagorean theorem! If you are making 20 x 20M grids then here is a hint, you make a triangular with measure tapes with one tape measuring 20M and one measuring 28.28M. Then you switch the tape measurements, make another triangle and now you have your first grid!

Now use the bamboo canes to stake in a tape along the base line. Imagine you have made a giant square on the earth and one side is now measurable. Stake in a tape opposite to the measurable side of the box and now you would have the “line monkeys” use the tapes as guides and stake the clotheslines over the tape. Now the data collection/fun can begin.

Simplifying matters (for those who aren’t experienced geophysicists), the surveyor would carry the geophysical device and collect data when the machine was over the colored tape of the clothesline. When one line is complete, they would move over a meter, turn around and start the process anew. Meanwhile the “line monkeys” would perform the “ritual dance” of unstaking the clotheslines and moving them into the next position. The line monkeys have to move around the surveyor so that the data collection is not stopped or compromised, least they have to redo the data collection for that line. Once the grid is complete, the tapes on either side are moved to the next grid, much like the movement of two inchworms, and the process begins again.

I hope that you understand some of the basics of a geophysical survey. Now here are some complications that occur. When you are working on a slope the tape measurements become inaccurate and the wind can catch the tapes like a sail and rip them out of your hands. When doing a magnetic survey the ends of the tapes have metal in them and have to be kept at least 2Ms away from the machine. As if thats not bad enough many farm animals enjoy chewing on the fiberglass tapes and knocking over the canes. Don’t believe me? Check out this picture.

Not the bambo cane!

Not the bambo cane!

Ridgewayus hic! (Ridgeway was here)

July 2, 2008

Last night I finished my geophysical tour of duty. At Scone we finished hunting for the Medieval Abbey and associated outbuildings with GPR. The last two days (The 25-26th of June) we investigated the proposed area of the Medieval village with a fluxgate gradiometer (which looks for magnetic anomalies bellow the ground). It turns out we were on the edge of a rig and furrow field (an old farming technique) and we might have located a homestead or a field building. We also scanned the nearby Skittery (sp?) ditch, which was a massive open sewage system. Sadly, this ditch was infilled in modern times and has a lot of metal in it, which effectively ruins any chances of interpreting the ditch feature.

I took Friday (June 27th) off. By took off I mean washed all of my non-magnetic outdoor clothing and readied myself for another batch of geophysics.

Saturday, June 28th, we traveled to Ecclefechan and set up a grid system at the Roman fort of Burnswark. There are actually two Roman forts, or castra (singular-castrum), based around a massive Iron Age hill fort. We primarily investigated the southern fort, which is a unique creature. The Iron age hill fort was excavated and thousands of lead slingshot were found in the ‘destruction level’. Originally thought to be a siege site, it is now thought that the hill fort was used as a training ground for the Roman. The fort has a smaller ‘fortlet’ within the typical double ditches of the larger fort. Also on the northern wall there are three mounds known as the ‘three brethren’. The purpose of these mounds is unknown. It is thought that they were created for an artillery platform for ballistae. Personally, I do not believe this as I think they are simple too close to the hill fort.

After a few days of thinking over their purpose, I have come to my own conclusion. I think that they are gateways modified to drain water away from the Roman fort. Many Roman forts have a rectangular wall a few meters out from the earthworks so that the Roman soldiers can control access to and from the fort. The fort is downhill from a very large hill, I think that water would easily enter and flood the Roman camp. I think that the standard gate system was modified with mounds so the water would collect in the ditch around the mounds and be likely be diverted away either outside the earthworks or through the double ditches. It is just a theory but any person who has camped downhill, especially in Scotland, will know just how a bit of rain can ruin your day.

There was 7 people in our crew, 95% were fellow post grads, and armed with two a fluxgate gradiometers and a resistivity meter (which compares the electrical resistance of ground) we covered a huge area. Under the watchful eyes of thousands of sheep we marched up and down the slopes to the sounds of beeps from our high tech devices and the bleating of sheep. It was a great experience and the longer you stayed at the base of that hill, the easier it was to envision Roman soldiers in testudo (tortoise) formation marching up to the hill fort with suppressing fire in the form of hails of lead sling shot. There may have been an actually Scottish opposition present (likely called  ‘Picts’ which roughly means “painted ones” due to the usage of body paint and tattoos) to return fire and clash in close combat  or it may have only been a daily drill. Only time and additional archaeological investigation will give us any answers.

Peacocks and physics er…geophysics

June 23, 2008

This is the first day of an entire week of geophysics. I am working at two separate sites and today was my first day at the site of Scone (pronounced like schooner without the er), Scotland. Scone is a medieval monastic site that is also the original location of the “stone of destiny”. I used ground-penetrating radar (GPR) for the first time. Affectionately referred to as  “the plough” or “the lawnmower” the GPR unit skims across the ground and as the wheel moves there is a sensor which triggers the transmitter unit and the data is collected by the receiver unit (which appears as white boxes which are slightly separated from each other). GPR is amazing because it can collect huge amount of data that allows for 3D analysis and, with enough luck, you can even tell exactly what is bellow the ground and what is it made of. We took readings every 5cm but the wheel sensor undertook all of the hard work and we managed to cover a huge amount of ground.

The work is being undertaken at Scone because it faired so poorly during the reformation. Most Catholic buildings had at least some standing elements left for archaeologists and historians to record, however, the landowners of Scone did not like to gaze upon a crumbling church and had any surface remains destroyed. Now almost nothing is known about the layout of the site itself.

It was a beautiful day for surveying and apart from tourists the site was plagued with peacocks. I have some great pictures of a seemingly interested peacock eavesdropping in on our geophysics discussions, however, because people are identifiable I won’t put them up yet (without consent). On the estate, there is an incredibly beautiful pure white (albino?) peacock. Given its uniqueness it was constantly harassed and tried to scare off these camera-happy predators by brandishing its tail. This defense mechanism would backfired and it would simply draw the attention of every tourist within view. I call it the “white peacock paradox”; I am sure there some underlying comment about the rich and famous in there somewhere.