Sawtooth Sunday

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

Today saw the GPR team doing the sawtooth edges of the field. A bit fiddly to do, but very fiddly to survey-in and process.  I have only processed one block of the three, I’ll work on the others tomorrow and also start joining the various blocks together into one big survey.  The  Resistance team also managed a very respectable six grid squares, including some that covered the east wing of the “House on the Hill”, otherwise known as Insula XXVI Building 2 or even Niblett and Thompson Monument 445…  This building was first published by Corder in 1941 and has only been seen through aerial photographs until we came on the scene.

First the underlying magnetometry data from 2015.

Fig. 1: the magnetometry data underlying the 2017 Earth Resistance survey.

As can be seen from Fig. 1 we can see the building quite clearly in the mag data as a series of white (low magnetism) lines.  The east wing does not show very clearly.

Fig. 2: the Earth Resistance survey.

The results from the Earth Resistance survey show the building beautifully.  The image has been high-pass filtered.  The large room on the east wing shows very clearly, although the “apse” on the west wall of it is still a little unclear.  It looks like a large dining room.

Let’s look at the 2015 and the accidental 2017 GPR surveys.

Fig. 3: the 2015 survey of the “House on the Hill”.

The slice from the 2015 survey (Fig. 3) shows some of the detail more clearly than the Earth Resistance survey, and some less so.  The other details may show more clearly in other slices and I’ll reprocess the data in due course. It will be interesting to see what the Resistance survey makes of the building to the far east of the GPR data.

Fig. 4: The 2017 GPR survey overlain on the other data.

Just for completeness sake, here is one of the time slices from the 2017 survey (Fig. 4).

Further south (and further up the hill!), the team completed a block to the south of the nice building we saw yesterday.  The new software can create an image with all the slices on.

Fig. 5: slices 3 to 10 of the day 4, block 3, GPR data.

This is useful to be able to see how the details change as one goes deeper.  (Take the depths given with a pinch of salt as 0.09m/ns is just a guess at the moment.)

The next series of images shows slices 4-8 from the above plotted next to yesterday’s building (just yesterday’s slice 5). The joins between blocks will improve when I process it all as one big survey.

Fig. 6: slice 4 (see Fig. 5 for depths).

Fig. 7: slice 5 (see Fig. 5 for depths).

Fig. 8: slice 6 (see Fig. 5 for depths).

Fig. 9: slice 7 (see Fig. 5 for depths).

Fig. 10: slice 8 (see Fig. 5 for depths).

As can be seen there are various buildings in this area.  It looks like there might be another small town house just the SW of the one we saw yesterday.  There is also something quite large parallel to the SW-NE road which shows in the deeper slices.  The large ditch which runs parallel to that building, just to the west which can be seen in the mag data, shows as a whiter line of “no reflections” in the GPR data.  There is quite a lot going on in this little block of data.

Tomorrow I will work on the other blocks and try to integrate the first four days of survey.  We are not out on site again until Wednesday.

Many thanks to Ellen, Jim, Mike, Graham, Nigel, David and Pauline for all their hard work, and especially to Mike, Jim and Ellen for transporting all the equipment as well as myself!



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