Geophysics at South Park
I’ve just got back from a meeting with Olaf & David Pinches at South Park,
where Olaf had arranged to meet up with Chris & Andy from the City Council’s Parks and Leisure Department. Chris (whose background is in archaeology!) is being really helpful towards the project, and has agreed to try a novel form of surveying – we are going to strap the GPS to the side of a tractor so that we can gather a whole load of info while Andy mows the park.
The GPS has a setting whereby you can get it to take readings at specified time intervals, say once every second, so in theory, we could get a complete survey of the park done in the time it takes to mow it. It is going to need a bit of fiddling with the attaching of the GPS to the tractor – the two main problems are going to be vibration, as a tractor has no suspension. The only thing that stops (barely, at that, from experience) the driver getting shaken to death is a sprung seat. The other one is the actual way of attaching the GPS – both Chris & Andy suggested cable ties rather than gaffer tape, which had been our first idea. The main point is avoiding a horribly expensive sound as the GPS drops off and promptly gets mowed, with extreme prejudice!
Olaf is going to meet up again with them when Andy brings the tractor and gang-mower along to have a go at sorting out the practicalities. After they had gone off to carry on working (this is about the busiest time of year for them, everything growing like mad and with the school hols, the parks being used like mad) we had a go at using the GPS in this automatic data collection mode. First we started off by doing an area near where we were (the entrance on Headington Road), all taking turns to do a bit, then we set off up the hill to so some more serious work.
David’s area of interest is (rather imprecisely) Oxford during the Civil War, which ties in nicely with doing a survey of South Park, as there are, hopefully, the remains of the earth-works the Parliamentarians set up to bombard the city which was the Royalist capital. You can see why – you get a marvellous view of the “dreaming spires” up there. After a little confab –
Dave set off at a brisk pace, walking up and down the hill, to get a mini survey covering a section of the ramparts. In the above photo you can also just about pick out the medieval ridge-and-furrow field system – the yellow Plantain is flowering along the tops of the ridges which you can see stretching diagonally across the photo. Cycling across the park must almost make you sea-sick, the ridge-and-furrows are so well preserved.
The purpose of all this hard work was to get some representative samples of the sort that the tractor might gather, so that Olaf can play around with it a bit, to see how it comes out. He is also going to look into if there is any LIDAR data for the park – but it’s a bit random as the main amount of data collection has been by the Environmental Agency for compiling flood-risk maps. Whether areas off to the side get looked at depends on flight paths, which rivers, and streams are their responsibility, and all sorts of other factors, so it’s a bit of a lottery, but worth looking at as the data is very high quality. You can manipulate it in all sorts of ways to bring out detail which might not be noticed under ordinary viewing.
We finished up and I gave David a lift back to Rewley House with the GPS (it packs into a rather unwieldy large red flight case) while Olaf went off to a meeting with Jane.
I’m carrying on preparing for a Test Pit which Gill and I are running, just off Cowley Road, tomorrow and Friday, which I think is going to be interesting – regardless of what finds turn up, the location is in the area of Cowley Marsh. We have been thinking about what precisely “Marsh” might mean. When we did a test pit in the Elder Stubbs allotments we came down onto sandstone after about 0.40 metres which doesn’t seem all that marshy. But do we know it is pretty damp around Bartlemas, so more information is going to be useful. As an aside, I was talking to Christopher Franks, who lives in the Farmhouse opposite Bartlemas Chapel the other day and he says that the trench around the Chapel, which was our “excuse” for last year’s dig there, is a great success. During the downpours earlier on this year, the chapel stayed dry throughout!
I’ll be back with what happens at the test pit this weekend and what Olaf comes up with from the survey.