Back to Gorhambury

When I woke at about 6am I could hear the pitter-pat of rain outside the window.  I groaned. Today was to see the start of the second season of work at Gorhambury.  Rain!  Just what we didn’t need.  I shouldn’t have worried as the rain soon stopped, and by midday the sun was out and the weather was warm.

My other worry was that a week ago we had no equipment.  The mag was being repaired, the GPR was somewhere in Oxford and the Institute of Archaeology’s nice new RM85 Resistance meter had yet to be delivered.  On Sunday we tested the mag… all seemed well.  Yesterday Ellen drove to Oxford to collect the GPR (she’s a star!), and UPS delivered the res kit.  Yay.  All ready to go.

We had a large team today consisting of a mixture of regular members and some new faces, mainly from the St Albans and Hertfordshire Architectural and Archaeological Society.  It was excellent to have such a large team allowing us to run all three instruments.  Many thanks to everyone who helped.

The new resistance meter has the ability to take two readings side-by-side, and does so very quickly.  I was very impressed with the first day we used it.  We managed five 20m x 20m squares at four readings per meter, even with a delay as we set it up.

The new resistance meter in action with St Albans Abbey in the background.

The new resistance meter in action with St Albans Abbey in the background.

We also completed eight 40m x 40m mag grids and two GPR grids, one 40 x 40m and one with a ragged edge.  The next image shows the mag survey of the entire town so far.

The town as surveyed so far.

The town as surveyed so far.

I’m starting to believe we might actually get the whole town, well the area available within the town, surveyed!  Zooming into the area we did today, we can see that we have picked up some more of the “1955 ditch”, the first-century boundary of the town first excavated by Frere in 1955.  It is the wide, straight dark linear feature which runs diagonally from the SW to the NE in the image below.

The area surveyed on day 19.

The area surveyed on day 19.

The annoying sensor-freeze struck again in the penultimate square.  Luckily it was only one line (the funny stripes are a result of the data processing) and we can re-do just that tiny bit and merge the data into the square in the software.  We mainly found ditches and pits (the dark blobs and lines), and are just getting to the busy area near the road.  There is a faint suggestion of a road behind the 1955 ditch, as we found in the southern area.

The resistance survey was a great success!  We did an area to the WSW of the theatre.

Location of the resistance survey.

Location of the resistance survey.

As I hoped, it picked up the road very clearly, but also picked up some of the details of the buildings.  The next two images show the resistance data and the mag data for comparison.

The resistance survey.

The resistance survey.

The mag survey for the same area as the previous image.

The mag survey for the same area as the previous image.

The GPR survey is just to the south of the res survey.  I have only processed the north block as it is too late to process the jagged-edged one too.  A number of walls and buildings are evident in the third and fourth time-slices.

Day 19 GPR survey, north block, slice 3 (14 to 18 ns).

Day 19 GPR survey, north block, slice 3 (14 to 18 ns).

Day 19 GPR survey, north block, slice 4 (18 to 22 ns).

Day 19 GPR survey, north block, slice 4 (18 to 22 ns).

The comparison with the resistance survey is also very interesting.  The GPR time-slices tend to show the walls better, but the resistance survey tends to show the road better.

Resistance survey overlain on the GPR and mag surveys.

Resistance survey overlain on the GPR and mag surveys.

GPR data from the same grids as the res survey in the previous image.

GPR data from the same grids as the res survey in the previous image.

Short and sweet posting this evening as we have another busy day tomorrow, but at least this gives you a feel for what we are now finding.

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