Tag Archives: Hertfordshire

GPR update

The rain has given me a chance to catch up on processing the GPR data. The procedures introduced by Mike Smith have made it much easier. Thank you Mike!

Here is an image of the whole survey so far:

The complete GPR survey after day 30.

The complete GPR survey after day 30.

That is roughly 7.5ha of GPR data.

Here is a detail of the area around the edges of which we have been filling-in the gaps:

The eastern side of the survey after day 30.

The eastern side of the survey after day 30.

Sadly, all that fiddly work has presented us with any nice clear buildings, but there are lots of bits of walls which join up with other things we have found.  When I process the data fully, we may well get more from it.  The one thing that does stand out are the triple walls of the temple just heading into the area of the theatre.

Lastly, Mike sent me this lovely picture entitled “Lonely archaeologist”.

The Lonely Archaeologist (c) Mike Smith 2016.

The Lonely Archaeologist (c) Mike Smith 2016.

Hopefully, it will be drier tomorrow, but with enough surface moisture to make the resistance survey easier!

 

 

Around the bend

We are within four grid squares of completing the “Theatre Field.” The sheer size of the field doesn’t really come across in the images. From the northernmost point to the southernmost it is 855m and it is 600m from east to west, enclosing an area of 27ha. That is about 38 soccer pitches in area!

The survey of the Theatre Field after day 28.

The survey of the Theatre Field after day 28.

But enough of all this nonsense about soccer pitches, I hear you cry, what about “the sinuous ditch”?  Well, here it is…

The course of "the sinuous ditch" after day 28.

The course of “the sinuous ditch” after day 28.

Yup, the ditch is now heading north again.  On a flat image, this looks really odd but when one is in the field it seems pretty clear that it is following the contour lines.  Perhaps we can still consider the ditch an aqueduct?  Here is a detail:

Detail of the area at the end of the sinuous ditch.

Detail of the area at the end of the sinuous ditch.

The section of the ditch surveyed today seems very broad, and gets a bit fuzzy near the big irregular feature shown in stronger black and white.  My guess is that the irregular feature is a later quarry pit — very common in the Hertfordshire countryside — and this may have partly destroyed the ditch.  Who knew that the last four squares might provide the answer to this mystery feature!  There are also quite a few weaker and more indistinct ditches in this area, along with quite a few pits.

The GPR crew worked their way steadily eastwards along the northern edge of the Theatre Field.  They have covered an amazing area too.  Remember that (a) they have to walk four times as far to cover the same area as the magnetometer and (b) their cart is dragging a plastic tray along the ground.  In longer grass it is quite a difficult task.  Despite this, look what they have now covered.

The total area covered by the GPR.

The total area covered by the GPR.

This image is a bit of a mish-mash of different time slices but it conveys the main message… look what we have covered!

Here is a detail of the last two days area:

Detail of the area covered during day 27 and 28 of the survey. Fourth time slice (15.5 to 18.5ns).

Detail of the area covered during day 27 and 28 of the survey. Fourth time slice (15.5 to 18.5ns).

The surviving wall foundations are easy to spot: the black lines looking like buildings!  We are, however, also seeing the outlines of building foundations in white where the stone has all been removed just leaving robber trenches.

The GPR data is just being fairly crudely processed here as it takes much longer to do than mag or resistance data.  At some point I will need to process it all in much more detail and much more consistently.  It does, however, give us an excellent comparison with the mag and res data even with this basic level of processing.

Tomorrow and Tuesday are our “weekend”.  We all deserve a rest!  Many thanks to everyone, I hope you agree it is worth the effort.

Almost round the bend

Today saw a slightly smaller team than we have had, but we still managed a good area of magnetometry survey and GPR, and even one small square of Earth Resistance survey.

First, the mag survey.  The team are starting to work their way north along the western edge of our survey area filling in between what we have already surveyed and the third century town wall which is hidden in the trees in the Google Earth image.

The magnetometry survey up to the end of day 24.

The magnetometry survey up to the end of day 24.

Looking at the area surveyed today in more detail, we can see the beginnings of the corner of the “1955 ditch”.

The area surveyed on day 24.

The area surveyed on day 24.

There is surprisingly little of anything much showing inside or outside the ditch in this corner.  The ditch is, however, slightly narrowing and bowing.  How curious!  Tomorrow should, fingers crossed, see us pick up the rest of the corner.

The GPR team, way down the hill near the drive, completed another 40x80m block.  Here are four 3ns thick time-slices.

Day 24 GPR, time slice 2 (9.5 to 12.5ns).

Day 24 GPR, time slice 2 (9.5 to 12.5ns).

Day 24 GPR, time slice 3 (12.5 to 15.5ns).

Day 24 GPR, time slice 3 (12.5 to 15.5ns).

Day 24 GPR, time slice 4 (15.5 to 18.5ns).

Day 24 GPR, time slice 4 (15.5 to 18.5ns).

Day 24 GPR, time slice 5 (18.5 to 21.5ns).

Day 24 GPR, time slice 5 (18.5 to 21.5ns).

The top image (time slice 2) just shows the noise in the ploughsoil.  The second image, however, shows a lovely little building 16.5m by 10m in size, aligned with the “1955 ditch”.  I’m not certain what this building is, it seems an unusual plan for a domestic structure.  The third image (time slice 4) shows this building, but also a very strong reflection from a wall on the eastern side.  Presumably this is part of a building which has been robbed out more thoroughly.  In the last time slice the signal has “attenuated” and we are only getting the strongest reflections showing.

The overall image gives some idea of how much we have now covered.

The area covered by the GPR at the end of day 24.

The area covered by the GPR at the end of day 24.

This image is a bit of a mismatched mishmash as the data was collected at different times and the time slices are somewhat variable as I have learnt to process the data over the last year.  At some point all the data will need to be reworked systematically, but that is beyond me while we are out collecting yet more data every day!

Many thanks to everyone who helped, and welcome to the people who have recently joined the team.  Your efforts are producing spectacular results.

 

At 1pm precisely…

The Met Office predicted rain at 1pm, and at 1pm it began to rain.  We had, however, managed to do four mag grids before lunch, and finished off another one and a res grid in the drizzle.  Many thanks to everyone who turned out on a unpromising morning and helped us complete a fair bit in the time we had.

The bad news first.  The Chess Valley Archaeological and Historical Society were kind enough to lend me their resistance meter and cable to try and work out what is wrong with ours.  Unfortunately, it looks like it might be the wiring on the resistance frame as the results we got today were utter nonsense.  Many thanks for John Glover for lending me the equipment and Jim West for bringing it over.

The five mag grids were, however, extremely interesting.  First the overall image:

The mag survey after Day 14.

The mag survey after Day 14.

Weather permitting, we should be up by the drive by the end of tomorrow, and hopefully will have picked up more of the ‘sinuous ditch.’ Zooming into the area we did today reveals some interesting features.

Detail showing the area surveyed on day 14.

Detail showing the area surveyed on day 14.

An annotated version of the previous image.

An annotated version of the previous image.

We have picked up the cross-roads between streets 11 and 25 very nicely.  Along street 25 there seems to be a line of smaller buildings.  More modest dwellings, perhaps, or maybe workshops and shops?  On the north corner, however, is a weird looking and extremely magnetic feature, probably a building as it seems too rectangular to be something else, and is approximately 20m by 10m in size.  Perhaps the building burnt down, or maybe it is an industrial feature?

Tomorrow we should be able to survey the grid next to our first “uber magnetic” building as well as picking up, we hope, some more of the infamous sinuous ditch.

We have also made the news on the Institute of Archaeology‘s website!

A grey day in Ashwell

The weather forecast wasn’t great, but we took a chance and headed up to Great Buttway, Ashwell End, to continue our survey before the grass starts growing and we have to take a break until after the first silage cut.  Great Buttway was surveyed ten years ago using a single sensor machine by Mark Noel.  The survey was excellent, showing all sorts of Iron Age and Roman features.  The only reason for re-doing it is that we are now able to survey at a higher data density allowing us to create sharper, clearer pictures..

A grey day surveying in Ashwell.

A grey day surveying in Ashwell.

Luckily for us, the rain held off and we managed to survey the equivalent of about 11 grid squares: eight whole ones and four partials.  An excellent day’s work.  Many thanks to Dave Minty, Nigel Harper-Scott and Jim West who joined Ellen and I today.

The dGPS I have been using has had its SIM card changed to another service provider.  What a difference that made, and laying in the grid was a breeze.  Amazing technology, really, and revolutionizes how easy it is to georeference surveys.

The survey in Great Buttway after day 6.

The survey in Great Buttway after day 6.

The survey has linked up the Roman settlement in the NW corner of the area with the Iron Age settlement in the middle of the plot.  A road, presumably Roman, runs NW–SE across the area past the inevitable modern services.

The Roman site at Great Buttway / Wayman's field.

The Roman site at Great Buttway / Wayman’s field.

The detailed view of the Roman site shows more enclosures either side of the proposed road.  We can even see post-hole buildings in the eastern enclosure.  A very pleasing result.

We are hoping to go back to the site next week.  Hopefully, it’ll be a little warmer!  Also look out for further postings about Verulamium and a survey in the Candover valley.

Datchworth Church

Something a little different this time. The CAGG team were asked a favour by the Parochial Church Council at Datchworth.  Basically, they are running out of space in the graveyard.  A local farmer has offered them some land to extend the cemetery, but because of the possibility of archaeological remains in the area they need to have an assessment done before they can extend the churchyard.  Some ten years or so ago, the Welwyn Archaeological Society did some limited excavations in the area prior to the building of their church hall, and so we were approached to see if we could do a geophysical survey.  The area which will be affected is quite small, so we did the mag survey of the entire field over a day and a half, during which time we managed a resistance survey at 0.5m spacing of the key area.

The resistance survey at Datchworth underway, 19/4/2014.

The resistance survey at Datchworth underway, 19/4/2014.

We undertook the survey over two days, the 13th and 19th April 2014.  The mag survey was finished by lunchtime of the second day and would have been even quicker if it wasn’t for the awkward shape of the field — resulting in every grid (bar one) being a partial.

Results of the magnetometry survey.

Results of the magnetometry survey.

The mag survey shows… not a great deal.  The important area to the north of the current churchyard shows nothing much at all.  To the east of the church there are some potential features, but the most likely area is the northern part of the survey.  This spot also has lots of lumps and bumps and the farmer thinks there may have been a building there.  The clarity of the survey is badly impacted by the large quantities of farm machinery parked there and a farm shed.

Results of the resistance survey.

Results of the resistance survey.

The resistance survey was much slower.  When taking readings every 0.5m, it takes a day to cover the area the mag completes in about 40 minutes!  The high resistance feature (shown in black) that runs along the western edge of the survey, is a bank running parallel to the ditch that runs along the road.  The other features are not visible on the surface.  High resistance features are usually things like roads, paths, walls and sold floors.  In this case, we appear to have a linear feature running N-S to the west of our survey area as well as a second one near the “moat” at the top.  I need to ask around a bit more before committing myself to a particular interpretation, but they are certainly too wide for a wall.

 

 

Little Hadham

Today we ventured out to the east of the county to survey near Little Hadham. We had done a little survey at the site last autumn but returned to examine a more fruitful looking field today.  Many thanks to all who turned out, we had quite a large team.  As we wanted to finish the area we knew contained features we worked on until 6pm.  I think the results were worth the effort.

Results of the survey on 6th April 2014.

Results of the survey on 6th April 2014.

The surface finds included late Iron Age and Roman pottery and it looks like we have a small enclosed farmstead with an associated field system.  Clearly the features go further to the south and east, and metal detector finds show that it continues to the west on the other side of the road.  Previous survey suggests there is not much more, if anything, to the north.

The ridges from the cultivation show in the plot as the lines to running east-west, and there is a little stagger error, but nothing too bad.  We can’t always survey on nice smooth parkland!

Another success for the CAGG team!