10 000 levels

To archaeologists a level is a spot height measurement on any surface. On Monday, Simon and I set out to take as many levels as possible on and around the New Laund Hill enclosure. This is the job we should have been doing the week before last but for the snow. Using the Leica GPS survey equipment we were able to cover the whole area with just under 10 000 levels in the four hours before he had to be back in University to go to a lecture.

We (that is the special directorial use of the word ‘we’ – Simon is going to do the actual work) are going to use this data to make a detailed computer model of the surface of the hill. The idea is that there may be subtle variations in the topography that show where buried archaeology is. Simon’s dissertation research is to compare this data with his geophysical results from the same area, to see which is the most helpful, and also how the results can enhance one another when they are combined.

SONY DSCTaking this number of levels with any other kind of survey equipment would have taken absolutely ages but the combination of the satellite positioning technology and automatic data-logging you get with the Leica (other differential GPS systems are available) makes the whole task much more do-able. Simon divided the hill up into 30 x 30 m blocks (roughly the same shapes as we had used for the geophysical surveys) and then walked backwards and forwards across each one carrying the GPS sensor. The data-logger on the Leica shows a live trail indicating where you have been as you do the survey but in practice it is much easier to have a physical marker to walk towards. Simon put a red and white ranging pole on either side of each square and walked between them while I moved the poles a metre at a time across the site. The data logger was set to collect a level every time it had moved a metre; therefore, each 30 x 30 m block should have given us around 900 levels. It took twelve of these squares to cover the whole area of the enclosure, which ought to have been the equivalent of 10 800 readings.

screenshot RTK survey

These are our readings plotted out in QGIS, each cross on the plot is the location of a single level. In the end we had just short of 10 000 readings. This is probably because some of our squares were a bit more trapezoidal than square. You can also see the area at the north west side of the survey where the hill is so steep that we were more concerned about not falling off than walking precise I m transects.

The next stage is for Simon to convert all of these spot heights into a computer model of the surface of the enclosure. These are usually referred to as a digital elevation model (DEM) or digital terrain model (DTM). Once he has done that I will try and grab an image of that to post up here too.

We had worked out that we needed to finish the survey by 1.30 to get back to Preston in time for Simon’s lecture. With a lot of sprinting between grid squares and no breaks we finished the 12th square bang on time. It was only when I woke up the next morning that I put two and two together and realised that therefore we would have each have done at least 10 km of walking/running to do this. Fell running is not my sport of choice – it hurts your legs.

Wildlife of the day on the way home was a pair of medium sized dark brown deer running by the road. They had no antlers and distinctive white patches on the rear. Poking about on the internet afterwards I think they must have been female Sika deer. I’m not sure that they really count as wildlife as they were only about three fields away from the Forest of Bowland Wild Boar Park – possibly they were escapologists.

Rick

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