Cloud Atlas

Nothing to do with David Mitchell’s brilliant novel but, after last week’s Ice Road Geophysical Surveyors antics, this week we have been mostly mapping the inside of clouds. We are still working on the various different kinds of survey on the New Laund Enclosure, all of which are parts of Simon’s BSc dissertation. He has been processing the resistivity data but is worried that by working when the ground is variously either soaking wet or partially frozen we will get less reliable data. Therefore this week we have switched over to working on the detailed topographical survey of the enclosure site. To do this we have been using the University’s new Leica GS15 survey system which is such an utterly fantastic toy that I am going to have to be very careful that the whole of the rest of the post doesn’t turn into an extended Leica commercial. This is so new that no-one in the whole university has had a play with it yet. Not being complete mugs, we spent Thursday surveying the car park before going any further afield. It’s always best to have the option of retreating to the office to read the manual when learning a new process, especially in the winter. As it happened, Thursday was a lovely day, sub-zero but dry and sunny, and the machine was a treat to use, even for a Luddite like me.

SONY DSC

Today it was a bit less clear, this was our view of Higher Fencewood Farm as we were climbing up the back of New Laund Hill. The temperature was a relatively toasty 2 degrees above freezing but a week of frost had left the ground completely solid, entirely justifying Simon’s decision to switch over to topographic survey. The point of this kind of survey is to measure as many points on the surface of the site as possible. These, and we will need many thousands of them, are then used to create a very high-resolution digital map of the surface of the hill. This will show us very slight changes in elevation, which are not detectable by eye, hopefully including the missing portion of the bank and ditch of the enclosure.

This sort of survey is only really possible on a large scale by using the automatic survey capabilities of something like the new Leica. This works in the same way as the GPS in a car or on a mobile phone but, whereas they are accurate to about the nearest 5 metres, this system is accurate to within a few centimetres (it can get better than that but not the way we had it set up today).

SONY DSC

The white thing behind Simon’s head is the aerial, which is detecting the satellites. In his hand he is holding the data logger which is automatically recording the height of the aerial every time it moves 1 metre across the surface of the site. Therefore, all Simon has to do is walk about on the surface of the hill, keeping the aerial at a constant height above the ground surface, and the survey gets done. You can even mechanise the moving about part of the process by putting all the kit onto a vehicle. For example, the East Oxford project have put a similar system onto a tractor – they have a post about it here.

With this set up the tricky part is making sure you walk in straightish lines and get an even coverage of the surface. This is why he is staring at the data logger as he walks. There is a live trail on the data-logger screen that shows him both where he is now and where he has already been. Today was mostly about getting the hang of using the system out on site and testing our ideas about what the best way to gather the data was. As the rain closed in what mostly got tested was our resilience and the proofing on our waterproofs. However, we did get an idea of what size blocks of the hill we can walk at once. We also know that we need to modify our carrying system for the aerial, as it was hard to keep it as steady as we wanted. We are thinking that we may adapt the body harness from the Bartington Gradiometer in future. Once this is in place we think we will be able to cover most of the hill in a single day.

Rick

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