GPR

Geophysics at Tintagel Castle: Non-invasive work ahead of the excavations

I am cheating on Day of Archaeology at little, as I am going to talk about work we at TigerGeo did in May, but that is being used to inform the very-much-happening-on-July-29th excavations at Tintagel Castle. We’ve been really excited to see the excavations progress over the last few weeks and can’t wait to get our hands on the reports and plans to go back to our own data with.

 

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Just getting the gear onto site was a challenge!

While there has been a lot of media attention about the excavations (see Sue’s excellent piece for the insider perspective), the geophysical surveys happened without much fanfare in May, in order to give us time to process the data and report it back to the dig team at CAU. We thought it might be interesting to have an insight into the work we did on site and the iterative process of interpreting, getting feedback and revisiting the data that we are engaged in. Most of the time, we don’t get such a great chance to see the excavations that follow our surveys so this is fantastic for us as we will be able to update our thinking and interpretations in detail.

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Magnetic Susceptibility readings being taken on the lower reaches of the southern terrace

So what did we get up to? The excavation team didn’t want to make such a drastic intervention on the site blind. They had target areas, based on what was already known or assumed about the site and asked us to look at them in more detail to allow them to better target their excavations. They were particularly interested in finding buildings from the post-roman period that had lain undisturbed by recent archaeologists, so they could look at them with fresh eyes and modern scientific methods. Any excavation is inherently destructive, and on sites as unique as Tintagel, it is important to minimise the impact of destructive research, so to help them do this we came up with a package of four complimentary methods:

  • Ground Penetrating Radar, which should be able to detect buried walls and surfaces
  • Earth Resistance Survey, which should detect the same things as the GPR, but using different properties of the material, giving us a ‘double chance’ to find them
  • Magnetic Susceptibility, a method that looks at how magnetisable a material is, telling us things about the presence of certain forms of iron. This can help distiguish between different activities taking place on site: we’d expect higher MS in areas of industry or settlement thanks to burning or heating, than we would in storage areas, for example
  • Terrestrial Laser Scanning, to produce highly detailed surface models to pin down the geophysical data but also very acurately located biulding platforms that had been recorded over the years by site archaeologists.
castle_wall_from_scanstation10

This isn’t a photograph, it’s part of the point cloud generated by the laser scanner. You can see the team on the right trying to stay out of the scan!

A lot of fun was had on site getting ourselves and our equipment into the right places. Unlike the dig team, because we had to be quite mobile, with heavy gear, we needed to use a rope-access team to provide safety lines for us, so there were a lot of logistics to contend with around making sure we could cover the right areas. We were on site for a total of about 8 days, and really enjoyed talking to visitors to the site about what we were doing and why: people were particularly interested in the laser scanner and we’ve had to edit a lot of tourists (and seagulls) out of our point clouds!

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KC getting the scanner as far along the southern terrace as possible!

So what did we find out? The earth resistance and GPR surveys taken together confirmed the locations of some of the walls and floors that have subsequently been found in the trenches, and hinted that the archaeology on the southern terrace had a different character than that on the eastern area. The magnetic susceptibility data also suggested clear differences between the two areas, with low values on the eastern area and higher values with internal patterning on the southern terrace. This suggested to us that on the southern terrace people were living or working, using fire either for heat and cooking or for industrial purposes. We could also see come strong patches of enhancement that lay between what were thought to be buildings, so we suggested there may be one larger building here instead. The eastern area showed no settlement related enhancement. So were the buildings there perhaps storehouses? Many of the already excavated buildings in this area have been interpreted as stores rather than dwellings.

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Earth resistance underway (with ropes!) on the southern terrace

The laser scans were useful not only to us but to the excavation team as well as they will form the basis for the topographical data being collected about the site. We were able to use them to make important topographic corrections to our radar profiles, without which interpretation would have been very difficult!

GPR survey on the southern terrace: this is where one of the walls was found

GPR survey on the southern terrace: this is where one of the walls was found

So, what next? Well, our first and most exciting job is going to be to get all the plans and sections back in from the excavation team and see how they match up with our interpretation, especially of the radar: we were able to survey a larger area than could be excavated, so we can refine our interpretation based on the dig and better predict what other walls and floors lie on the southern terrace. Ideally, we’d like to come back and do even more radar and see if we can cover the entire southern terrace: this might give us the best chance of understanding the exciting structures there and their immediate context. We would also like to do more scanning to provide detailed topographic data for the entire islands. The Tintagel Research Project is set to continue, so watch this space….

You can see more photos from our work on facebook!

You wouldn't beleive how many of these we had to delete from the sky in our scans!

You wouldn’t beleive how many of these we had to delete from the sky in our scans!

 

Arghhh, please, not one of THOSE days!!

After spending a beautiful, sunny day in the field gathering geophysical data, the office awaits me. Data must be processed, they said!

There were no problems with the GPR and magnetometry. The site was a nice, even lawn and like a football field. It was a location near the Dutch coast with clear blue skies & fish for lunch. What a way to collect your data!!!

But the problems started the day after.

8.00 am

Euhm, where is my backup USB with the data? Can’t find it. And who took my fieldlaptop this morning?

Please, do not let this happen to me.

Oh, there it is. Pfew

9.00 am

processing GPR data. Hmmm, there are a lot of fielddrains visible in the data. This former soccer field clearly needed draining. I hope it doesn’t obscure my relevant data too much.

Oh, thanks very much, this visual basic software from a previous century keeps crashing. What is wrong, and where is the corrupted file? Checking lots of files one by one.

10.00 am

several  phone calls:

  • ‘yes, sir. We can do that. Oh, you want us to do the survey by the end of this week? Hmmm.’
  • ‘oh, were you expecting the report yesterday?’
  • ‘No, sorry. We can’t go any lower with our costs. Yes, you’re free to look for another geofyzz company.’

11.00 am

Oh, my God. I can’t believe the amount of recent rubble just below the subsurface. This red brick demolition waste is masking my magneto-data. Let’s see if I can fix this. Sigh.

The small archaeological excavations from the 80’s and 90’s do provide additional information, but why do their pits/trenches have to be so visible in my data! Go away!!

12.00 pm

Blue screen of Death

13.00 pm

Yep, several of those phone calls you do NOT want to deal with right now.

But just have to.

14.00 pm

Oh great, I have an inbox full of email. Let’s see if some procrastination will make my day.

14.30 pm

Euhmm, do you really want a financial forecast of these projects? You mean as in right now? But…

15.00 pm

postprocessing, filtering, enhancing, gnashing of teeth, munching pencil stubs. Login to GIS failed. Out of memory. Why am I not out in the field? Merrily singing aloud while gathering data. HELP!!

16.00 pm

But WOOT? Is that….yes..the former foundations. Hurray, here they are! And the results from the GPR differ from magnetometry, but combined they give very interesting anomalies.

Let’s make an appointment with the archaeologist to start some interpretation next week.

While humming a joyful tune, I shut down my computer.  Another day at the office. While all the odds seemed working against me today, I obtained some very interesting results.

Big smile!! I do love geofyzz.

walking with magnetometry multisensor cart

Walking with magnetometry multisensor cart

GPR behind the quad

GPR behind the quad

disturbances in the mag-data

Disturbances in the mag data

interesting features!

Interesting features!

lots of drains!!

Lots of drains!!


DoA, Digi-Arch, and Geofizz

Jess' Desk

Jess' Desk

After much delay, I’ve finally sat down to write my Day of Archaeology post. Yay! As some of you might already know, I’m one of the co-organizers of the event along with Andy, Stu, Tom, Matt, Lorna and Dan. We’ve been working hard on the event for many months now, so it’s been totally amazing to see everything go so well! I’m still in the process of reading over the many many posts from around the world – it’s truly exciting to see that so many archaeologists turn out to share their experiences.

Today (yesterday!), as many of you can probably guess, I spent the majority of the day 9am – 9pm holding down the DoA inbox. We were still issuing logins at 9pm, which is a testament to the entire event I think. In the words of Lorna, “We done good”.

But when I’m not doing the DoA, I’m actually a partner and archaeologist at L – P : Archaeology, a commercial archaeology partnership based in the UK. My work at L – P usually entails being a jack of all trades, but mostly with a technological spin. I’m very involved with our open-source archaeological recording kit (ARK) and provide support for many of the projects which are using it in the field (as mentioned in Andy Dufton’s post!). We also do lots of work with HLF funded projects which often involves creating websites for community groups wishing to branch out into the digital engagement side of archaeology. Most of this is usually done from my desk in our London Office.. featured left!

Portus Hyperbola

Portus Hyperbolas

On top of that, I’m also in charge of geophysical surveys for L – P and can often be seen pushing a pram (GPRrrr!), stylishly wearing no metal, or yelling at my computer screen full of black and white blobs.. :-S I’m very grateful that the geophysics gets me out of the office once and a while, that’s for sure! Currently I’m processing a load of GPR data for the Portus Project, which is (as always) turning up lots of interesting results for the team. (See lovely hyperbola(s) on right)

But I guess that’s about it for now. I’m pretty shattered from the last few days of helping with the DoA and juggling my work responsibilities. And now I shall shoot off for an afternoon in the pub to celebrate everyone’s hard work. Many, many thanks to everyone who made it such a great day. If anything I really hope that these sorts of events will not only raise awareness about the true (and diverse!) nature of archaeology as a discipline, but also highlight the sorts of things that are possible when we all just open up and share what makes us all passionate about archaeology. Thanks again!