THE SURVEY
The archaeological surveys took place between Thursday 10th March and Saturday 19th March 2016. There was also an Open Day on Saturday 19th March where visitors found out about the surveying process and the history we had gathered so far.
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We used three (or strictly speaking, four) different forms of survey: geophysics (resistivity, magnetometry); tape and offset; and LIDAR.
Whilst these methods are very different in the way they are carried out, they all had the same aim – to assess the nature of the archaeology at Under Whitle (both the lumps and bumps we could already see, as well as any hidden archaeology) and to help us decide where the best places to excavate were.
Tape and Offset Survey
This can also be called ‘baseline offset’ survey, involves using an old-fashioned tape measure stretched across an area of the site to create a baseline. This is usually done on a North-South or East-West alignment. Another tape measure is then used to measure from archaeological features on the ground e.g. lumps and bumps, to this baseline. These measurements are taken at right angles and are then recorded on a sketch plan of the area or simply written down, ready to be drawn to scale on graph paper, in our case, in the warmth of the Dove Valley Centre.
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All core volunteers received training in this type of survey on the first two days (10th & 11th March, 2016). There was also the opportunity for teachers to undertake this training too, so they could learn new skills and support their pupils/members of their group when they came later on in the survey. This took place on the afternoon of the 11th March 2016.
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When schools and groups visited, they were shown what to do, and contributed to drawing sketch plans, the taking and recording of measurements in the field and drawing up plans to scale in the Dove Valley Centre.
Read more about what pupils of St Thomas More’s Catholic School and Buxton Community School got up to, as well as members of the Peak District Young Archaeologists’ Club when they visited and took part in the survey.
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Geophysics
We used two different methods of geophysical survey on Peeling Back the Layers. These were magnetometry and resistivity, and we were delighted to have Trent and Peak Archaeology (part of York Archaeological Trust) on board to undertake them!
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Magnetometry measures and maps magnetism in the soil. We don’t do this just for the sake of it, though. Minute variations in soil magnetism in relation to the general background magnetic field can indicate signs of past activity (archaeology) under the ground. This shows up as a higher or lower reading. Areas of burnt material are generally higher and show up darker/black. Walls are generally lower and show up lighter/white. Bacteria can also alter soil magnetism which usually happens in wet soil and can indicate old river channels etc.
We hoped that this would be useful in our investigations at Under Whitle, for there are a number of residences/houses mentioned in documents that there is little trace of on the ground. Find out how useful the magnetometry proved to be on our Discoveries page!
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Magnetometry, however, is hopeless if there is interference from magnetic materials. Whilst we were sure there was nothing to cause interference in the immediate landscape, e.g. metal fencing, there were a few rules that the person undertaking the survey had to follow, such as no watches, credit cards or metallic zips. As magnetometry is a relatively speedy process, where the practitioner has to walk at a consistently quick pace along each transect to keep up with the beeps, the survey proper was carried out in the main by staff of TPA, although participants were able to handle the equipment and learn how it all worked.
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Resistivity is another technique we used. Similar to magnetometry, this method measures variations underground to detect hidden archaeology. Resistivity, as it names suggests, measures resistance in the soil to an electrical current passed through it. The resistance is measured and plotted.
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Everything has some resistance to an electrical current but ditches that have a lot of moisture content have less whereas walls and stones have much more. So, like the magnetometry, this technique should’ve helped us locate any missing buildings as well as other past activity. Visit our Discoveries page to see if this was the case!
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The two techniques together provide not only different data sets but also some confirmation for what each one finds. So, as well as helping us locate hidden archaeology that we went on to excavate, this allowed us and participants in the project to compare and contrast the different techniques.
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Click on the links to read about what pupils of St Thomas More’s Catholic School and Buxton Community School got up to, as well as members of the Peak District Young Archaeologists’ Club when they visited and took part in the survey.
LiDAR
LiDAR stands for Light Detection and Ranging, and is a surveying technique that provides very accurate, high resolution 3D data. This survey has been undertaken on behalf of the project by the Environment Agency.
LiDAR is useful for many things in the field of archaeology, such as locating archaeological sites in dense undergrowth and beneath otherwise impenetrable forest canopies. Although Under Whitle isn’t known for its forests, LiDAR can also help distinguish features that are otherwise difficult to discern using other methods. In addition, it can cover a much larger area than can, say, geophysics.
Below is a map of the area that is covered by the LiDAR survey (the area is that defined by the red line).
We have received the data from the Environment Agency and various individuals involved in the project have been having a look, and a multitude of interesting archaeological features have been revealed – not only those we can investigate further at Under Whitle but also across a wide area of the parish of Sheen – just look at the map above to see what has been included (if you click on it, the image will open in a new window so that you can see it better).
Using LiDAR is also helping to confirm results of the geophysical and tape and offset surveys, and allowing us to compare and contrast the different methods.
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If you would like to find out how we’ve been getting on, click here for our latest blog posts about LiDAR.