Anyone new to this blog or geophysics in archaeology is recommended to read the material on the “Geophysical survey in archaeology” page.
Saturday night I said the weather was predicted to be “unsettled”. Well on Sunday at 10am it was raining cats and dogs. (I wonder why cats and dogs? Why not ducks and pigeons?, or frogs and mice?) I was determined to set-out grids in Church Meadow and so I soldiered-on. Up until now, I have stuck to the 40m grid based on the OS for all the fields we have surveyed in Verulamium Park and in Gorhambury. Church Meadow, however, is a long thin field at approximately 45º to the OS grid. Additionally, the fence along Gorhambury drive is very straight for much of its length. I decided, therefore, to use a floating grid to minimise partial grid squares and wheel spinning. The lack of an “end line” function is the Foerster’s Achilles’ heel. We must have wasted hundreds of hours spinning the wheel due to that one simple omission. Although the data processing involves some extra steps and jiggery-pokery to get the plot in the right place, it seems worth it in this case. I think my decision was vindicated when the team completed nine complete 40x40m grids despite the wet start to the day, and the lunchtime deluge. Figure 1 shows the team in action.
Figure 2 shows the location of Church Meadow.
Looking closely at the Google Earth image reveals some features in the field (Figure 3).
With these features we had high hopes. Figure 4 shows the results of the mag survey from the first day.
Sadly, the plot is dominated by the two pipelines running through the field (Figure 5).
One of the pipes clearly runs straight through the building seen in the GE image. There are, however, some archaeological features to be seen (Figure 6).
It is very frustrating that we can see the walls in the mag data to the SW and between the pipelines, but the image is so dominated by them that it is hard to make sense of anything. Hopefully the res or the GPR will show the details better. The ditch is interesting, however. Could this be the vallum monasterii? It could, perhaps, be related to Watling Street, or it could simply be the remains of the earlier route of Gorhambury drive. It will be fascinating to see where it goes.
The Earth Resistance team completed an excellent six blocks of data. Figure 7 shows the whole res survey.
With good luck and a fair wind we should reach the hedge line on the next survey day. Figure 8 shows the grids completed on Sunday.
Not a great deal is showing in those grids apart from the faint line across the top corner. Let’s look at the mag data from that area (Figure 9).
The light line in the res data is matched by the dark line of “the sinuous ditch”, which is exactly what we would expect. The sinuous ditch is, we think, the town’s aqueduct. We should pick-up much more of this on Wednesday.
The GPR team have been working down the western edge of the town with the end in sight. Soon, soon, they hope, they can escape the theatre field and its rugged terrain (Figure 10).
The GPR team have been doing a lots of sawtooth edges as well as extreme hill-climb GPR. Figure 11 shows recent results.
GPR, perhaps even more than Earth Resistance, is affected by the weather and ground conditions. It seems very difficult to get different days to match-up. I tried three methods with this data collected over four days, and none were perfect. This image was created by just treating everything as one big data set. It doesn’t help that each tweak to see what works takes half an hour to process!
Looking back over the first three weeks, we have managed to achieve quite a bit despite dry weather, wet weather and endless partials. Many thanks to everyone who has been involved, especially those stalwarts who come most days (you know who you are!).
Nigel wonders what next week will bring…