Apse mad

We had a very successful day. It was grey and a little drizzly first thing, but true to the forecast it warmed up and turned into a gloriously sunny, if a little windy, day.  The mag team got right into the deep south and have made the mag plot look very tidy.

The magnetometry survey at the end of day 23.

The magnetometry survey at the end of day 23.

The team were determined to finish off the last few partial grid squares.  I think they were fed up walking the 650m from the cars!  The next swathe of grid squares will head north completing the Theatre Field at last.  Let’s look at the area surveyed today.

The area surveyed on day 23.

The area surveyed on day 23.

The band of buildings running from the NE seems to meet the 1955 ditch at a point where the magnetic response from the ditch changes markedly.  Perhaps the ditch was more deliberately filled-in here?  To the SW of the 1955 ditch there are fewer clear indications of stone buildings, but there are many linear features (probably ditches), and “blobs”, probably mainly pits but some of them are very large.  Of particular note is the small square enclosure right up against the town wall towards the south (seen as a black square).  One wonders what this was so close to the third century town wall.

At the other end of the field, the GPR crew managed another 80x40m block of data.  Apparently, nothing much was showing.

The day 23 GPR block (fourth slice, 15.5 to 18.5 ns).

The day 23 GPR block (fourth slice, 15.5 to 18.5 ns).

I beg to disagree!  Another small apsidal building is showing in the data, overlying the line of pits.  There is a large, rectangular, building to the west of it.  Are apsidal buildings the geophysicist’s version of busses?  One interesting aspect of this building is that it does not show in the mag data at all.

The same area as the previous image showing the magnetometry data.

The same area as the previous image showing the magnetometry data.

This is a great example of why undertaking both the GPR and the magnetometry surveys is so useful in giving a fuller picture of the town.  The GPR surveys are getting quite extensive!

All the areas surveyed with the GPR on the Gorhambury side of the town.

All the areas surveyed with the GPR on the Gorhambury side of the town.

The earth resistance team completed another excellent five 20x20m squares.

The earth resistance survey after day 23.

The earth resistance survey after day 23.

We can see some more buildings and bits of road, although there are some very high resistance areas.  One weakness of resistance survey is that there can be underlying variations in the data related to factors such as slope or geology which mask the archaeological patterning.  We can, however, apply a “high pass filter” which attempts to remove the underlying background trend and show the sharper differences more clearly.

The earth resistance survey, high pass filtered.

The earth resistance survey, high pass filtered.

The technique can create some artefacts in the data, but is very useful for bringing out some of the buildings.

Tomorrow and Tuesday are our “weekend”.  Many thanks for everyone who joined in during the first week, and here is to the next three!

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