A postdiluvian survey

Anyone new to this blog or geophysics in archaeology is recommended to read the material on the “Geophysical survey in archaeology” page.

Yesterday’s survey was called off due to rain. Not the usual English wet weekend in September sort of rain, but real rain. We had over 20mm at home, and I guess St Albans was much the same.  Many thanks to Anne, Julia, Pauline, Mike, Grahame, Joe and Dave for braving the damp conditions. I think it says a great deal as to how dry the preceding months have been that it still didn’t seem particularly muddy underfoot.  We managed a good six 20×20 grids with the Earth Resistance meter, including one awkward one with a big oak tree in the middle, and a 40x60m block of GPR.

Fig. 1: the Earth Resistance survey after three days.

As can be seen in Fig. 1, we have picked-up a nice courtyard building to the east near the road.  This isn’t listed in Niblett and Thompson or is it on the UAD, so this is a nice addition to the corpus.  We can see it in the mag data as well.

Fig. 2: the magnetometry data for the same area as Fig. 1.

It is a little clearer in the resistance data. It shows in the GPR too, much some features more clearly and some less.  A combination of techniques should give us a nice result.  We have covered quite large area with the resistance meter now (Fig. 3).  The difference between last year’s survey and this is simply in the processing.  I have applied a high-pass filter to this year’s data.  Once we have joined the two areas up, I can apply the same processing to the whole survey.

Fig. 3: the total area surveyed with Earth Resistance.

The GPR undertook the two grids to the west of the “House on the Hill”.  Here are four time slices, each just over 3ns thick.

Fig. 4: time slices of the area surveyed today.

As can be seen, we have multiple bits of buildings, but nothing (yet) that forms a coherent plan.  The curious empty SW-NE band persists.  This is in a small dry valley running downhill to the Ver.  Was it empty in the Roman period?  Has the archaeology eroded away, or has the archaeology been buried by alluvium?  Impossible to say at the moment.

The next three figures give time slices 5 and 6 with the other GPR data from this field (all just one slice).  The greyer (is that a real word?) images to the SE are this year’s survey, the brighter images to the NE are surveys from 2015 and 2016.  The detached block is today’s survey.  (We will complete the block to join it to the House on the Hill tomorrow.)

Fig. 5: time slice 5 with previous survey results.

Fig. 6: time slice 6 with previous survey results.

Fig 7: the magnetometry data underlying the GPR surveys.

Tomorrow we will be back, extending both the Earth Resistance and GPR surveys yet further.

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