Old Sarum Update

For the last few weeks a fair amount of preparation has been undertaken by various members of staff at the University of Southampton for a press release on the fieldwork conducted at Old Sarum (see previous blog post http://kdstrutt.wordpress.com/2014/04/21/in-the-castle-called-seresberi-old-sarum-and-a-new-survey-of-the-inner-and-outer-baileys/). Peter … Continue reading

For the last few weeks a fair amount of preparation has been undertaken by various members of staff at the University of Southampton for a press release on the fieldwork conducted at Old Sarum (see previous blog post http://kdstrutt.wordpress.com/2014/04/21/in-the-castle-called-seresberi-old-sarum-and-a-new-survey-of-the-inner-and-outer-baileys/). Peter Franklin and colleagues at the press office have worked hard to produce the finished story, and today things finally came together with a bit of a whirlwind of media attention. The finds of the project to date illustrate the potential of non-intrusive archaeological methodologies to elucidate on the archaeology of a particular site or landscape, without harming the material culture and with some strong underlying scientific concepts on which to base  some degree of interpretation and narrative.

Greyscale image of the magnetometry from the south of the outer bailey (top) and the interpretation plot for the data overlaid on LiDAR for the area (© LiDAR data Environment Agency copyright and/or database right 2014. All rights reserved.)

Greyscale image of the magnetometry from the south of the outer bailey (top) and the interpretation plot for the data overlaid on LiDAR for the area (© LiDAR data Environment Agency copyright and/or database right 2014. All rights reserved.)

The step from geophysical survey data to coherent archaeological narrative is a big one, and one of the reasons that our interpretations to date err on the side of caution. What is apparent from the results is the urban plan of a substantial medieval city, and an array of different forms of structure and associated features in the outer bailey at Old Sarum. Hopefully the results and their wider dissemination at this stage will help to generate interest in the site, the methodology used, and the wider applications of these approaches to archaeological research.

To date the results have been reported in a number of sources. Online the sources include:

BBC News   http://www.bbc.co.uk/news/uk-england-wiltshire-30300837

The Independent   http://www.independent.co.uk/news/science/archaeology/archaeologists-find-vast-medieval-palace-buried-under-prehistoric-fortress-at-old-sarum-9898759.html

The Telegraph   http://www.telegraph.co.uk/earth/environment/archaeology/11269753/Medieval-city-uncovered-by-archaeologists-and-not-a-spade-in-sight.html

More will hopefully follow tomorrow. Above all else the results show the pertinence of student involvement in research-led teaching, from developing an understanding of the archaeological and scientific theory for the work, to dealing with practical aspects of survey and undertaking fieldwork, to being involved in the processing and interpretation of data. The results at Old Sarum are testament to the peerless hard work and dedication of the students on the project, as well as the staff involved in their supervision.

Notes:

For images or for interviews with Kris Strutt, please contact Peter Franklin, Media Relations, University of Southampton. Tel: 023 8059 5457 email: franklin@southampton.ac.uk

For more information about the Archaeological Prospection Service of Southampton (APSS) visit:http://www.southampton.ac.uk/archaeology/research/groups/archaeological_prospection_service_southampton.page

 

For more about the Old Sarum and Stratford-Sub-Castle Archaeological Survey Project visit: http://www.southampton.ac.uk/archaeology/research/projects/old_sarum_and_stratford_sub_castle.page

 

For more information about Archaeology at Southampton visit: http://www.southampton.ac.uk/archaeology/index.page

For more information about English Heritage visit: http://www.english-heritage.org.uk/

Through world-leading research and enterprise activities, the University of Southampton connects with businesses to create real-world solutions to global issues. Through its educational offering, it works with partners around the world to offer relevant, flexible education, which trains students for jobs not even thought of. This connectivity is what sets Southampton apart from the rest; we make connections and change the world. http://www.southampton.ac.uk/

http://www.southampton.ac.uk/weareconnected

 


Guest Blog: Clare Allen – The Defensive Role of Basing House and its Environs

Student Basingstoke Common Survey Project We’re very happy to share the details of another fantastic project that will be happening at the same time as our dig. Postgraduate student, Clare Allen, will be working at Basing House for the duration of the excavation, to investigate the surrounding landscape of the Civil War period of the […]

Clare Allen

Clare Allen

Student Basingstoke Common Survey Project

We’re very happy to share the details of another fantastic project that will be happening at the same time as our dig.

Postgraduate student, Clare Allen, will be working at Basing House for the duration of the excavation, to investigate the surrounding landscape of the Civil War period of the site. Clare has written a guest blog post below about her plans.

Look out for Clare on Basingstoke Common when you come to visit us at the excavation!

Introducing Clare

My name is Clare and I’m a Masters student from the University of Southampton. I am carrying out my MSc in Archaeological Survey and Landscape. Consequently, this has led me to become interested in the application of geophysical survey techniques and how they can aid our archaeological and historical understanding of complex sites  such as Basing House.

Project Description

The purpose of my thesis is to understand the defensive role of Basing House through the application of Geophysics on Basingstoke Common. The main aims are to gain a greater understanding of the site within the broader landscape by examining the defensive features in the immediate area surrounding the grounds (Basingstoke Common).

It has been suggested that Basing House was ‘the scene of one of the most stirring acts of defiance that the country of Hampshire has ever known’ (Allen et al, 1999: vi).

Due to its defensive structures and location it was able to withstand defeat for three years, undergoing countless attacks.

Methodology

Through the use of magnetometry and potentially resistivity, I hope to discover some magnetic anomalies that will aid our understanding of Basing House and the defensive role it has played throughout its existence. The site will be divided into 30m by 30m grids expanding southwards down the common.

Once the gridding is complete the following geophysical techniques and methods implemented:

  1. Magnetometry survey using two Bartington Instrument, Grad 601 dual sensor fluxgate gradiometers. The magnetometry survey will be carried out at 0.25m intervals along traverses spaced 0.5m apart.
  2. Resistance survey will hopefully be undertaken using a Geoscan Research RM15 resistance meter, to 0.1 Ohm. Readings will be taken at 0.5m intervals along traverses spaced 0.5m apart in order to gain a higher resolution of results. If time allows it will be useful to get some grids covered with the resistance meter. On the areas that are showing magnetic anomalies, it would be useful to use the two techniques in conjunction with each other to build a greater comprehension of the site.
Figure 1: Shows the fluxgate gradiometer being used during the spring survey season by the University of Southampton.

Figure 1: Shows the fluxgate gradiometer being used during the spring survey season by the University of Southampton.

Once the data has been collected and processed I will be able to generate a series of digitised overlays in order to interpret the features that are appearing. In conjunction with the excavation season taking place from 22nd July – 11th August, more interesting information about the history Basing House should emerge.

Figure 2: Planned survey area [Area A indicating the first area to be surveyed, which will extend westwards into survey area B].

Figure 2: Planned survey area [Area A indicating the first area to be surveyed, which will extend westwards into survey area B].

 


Filed under: Clare Allen, Student Research Post, Summer Excavation Tagged: basingstoke common, clare-allen, common, defensive role, fluxgate gradiometer, geophysics, geoscan, magnetometry, postgraduate, research, resistivity, survey, surveying

Guest Blog: Will Heard – Spring 2013 Survey Results Part 2

Last week we published a guest post from Will Heard, as a summary of the Spring Survey that the University of Southampton students carried out this April-May. Here is Will’s second and final blog post about the survey results. Thanks again to Will! — Basing House Spring Survey Part 2 by Will Heard, 2013 Will […]

Last week we published a guest post from Will Heard, as a summary of the Spring Survey that the University of Southampton students carried out this April-May. Here is Will’s second and final blog post about the survey results.

Will Heard

Will Heard

Thanks again to Will!

Basing House Spring Survey Part 2

by Will Heard, 2013
Will is a third year undergraduate student, with interests in survey, geophysics and the use of computers for archaeological purposes. He is interested in any period of history, having worked at Basing House and on a Bronze Age site amongst others.  He is currently working on his undergraduate dissertation, which aims to use GIS systems to reveal the theoretical effectiveness against invasion of a small section of the World War II G.H.Q Line in Essex.

The Motte Resistivity Survey

Figure 2 shows the resistivity plot of part of the Motte interior with notable features enclosed in coloured lines. The bottom left high resistivity feature is most probably related to the still accessible cellar, which can be seen as a large depression on the contours.

The  high resistivity feature at the far bottom of the image has no associated topographic evidence, but it is situated in a position that may suggest it is a continuation of the feature running parallel to the cellar. If this is so, then the high resistivity feature next to the cellar may not be directly related to  it after all. The other most interesting feature is the slight low resistance feature highlighted in green, which represents a dip on the topographic model. The ground raises up to a point which is a well (circled white in Figure 3). The presence of the well leads to the assumption that this area was some sort of courtyard or open air space. This is supported by Peer’s plan of his excavations (Figure 1).

Figure 1 - Plan of the Old House as excavated by Peers. After (Royal Archaeological Institute 1924: 362).

Figure 1 – Plan of the Old House as excavated by Peers. After (Royal Archaeological Institute 1924: 362).

Figure 2 - Resistivity Survey of part of the motte interior. Notable features are enclosed by coloured lines. Negative ohm values caused by the high pass filter. Contours from a raster. ArcGIS 10.1.

Figure 2 – Resistivity Survey of part of the motte interior. Notable features are enclosed by coloured lines. Negative ohm values caused by the high pass filter. Contours from a raster. ArcGIS 10.1.

Figure 3  - Motte interior resistivity draped over the 3D TIN surface. From the north. Light from the east at 45 degrees. Vertical exaggeration at 1.5.

Figure 3 – Motte interior resistivity draped over the 3D TIN surface. From the north. Light from the east at 45 degrees. Vertical exaggeration at 1.5.

The New House Resistivity Survey

The New House site was the largest of the three areas surveyed with Resistivity and has a lot of strong features. The most obvious features are the straight lines along the entire left side of Figure 13. These are undoubtedly buried foundations of the raised New House.

The circular anomalies are towers of the sort seen in Hollar’s drawing (see Figure 15). The strength of these anomalies suggests excellent preservation and indeed, an excavation uncovered some of these remains and did not fully fill in the trenches. The resulting depression in the topography can be seen in the foreground of Figure 14.

The very low (white) anomalies in the same area are possibly caused by a slow build-up of moist, humic soils in the unfilled excavation trenches. Given the aforementioned evidence, it appears unlikely the anomalies are of historical origin. However, further south in Figure 13, some of the unexcavated strong circular anomalies enclose areas of extremely low resistance. These may be the result of filled sunken floors, or quarrying straight after the final Civil War siege.

Another area of interest is on the right of Figure 13, which is circled by a green line. This area is highly variable, with pixels of very high and low resistance and it is unclear what these readings represent. More areas of interest include the horizontal line feature and various other patches of high resistance in Figure 13.

Figure 4 - Resistivity Survey of the New House area. Notable features are enclosed by coloured lines. Negative ohm values caused by the high pass filter. Contours from a raster. ArcGIS 10.1.

Figure 4 – Resistivity Survey of the New House area. Notable features are enclosed by coloured lines. Negative ohm values caused by the high pass filter. Contours from a raster. ArcGIS 10.1.

Figure 5 - New House resistivity plot draped over the 3D TIN. Red lines show features with associated topographic variations. From the north. Light from the east at 45 degrees. Vertical exaggeration at 1.5. ArcGIS 10.1.

Figure 5 – New House resistivity plot draped over the 3D TIN. Red lines show features with associated topographic variations. From the north. Light from the east at 45 degrees. Vertical exaggeration at 1.5. ArcGIS 10.1.

Figure 6 - Wenceslaus Hollar's 'The Siege of Basing House'. The text reads 'A THE OLD HOUSE. B. THE NEW. C. THE TOWER THAT IS HALFE BATTERED DOWN. D. KINGS BREASTWORKS. E. PARLAMENTS BREASTWORKS' [sic]. After (Wikipedia 2013)

Figure 6 – Wenceslaus Hollar’s ‘The Siege of Basing House’. The text reads ‘A THE OLD HOUSE. B. THE NEW. C. THE TOWER THAT IS HALFE BATTERED DOWN. D. KINGS BREASTWORKS. E. PARLAMENTS BREASTWORKS’ [sic]. After (Wikipedia 2013)

Everyone was very pleased with how the survey went, despite some bitterly cold days and an afternoon of menacing weather in the first week. I hope that these highlights from the data illustrate just what can be done with all the data we gathered although someone more savvy with the computer software could do things much more impressive than this. Various sub-surface features were linked to surface features observable on the topographic model.  Some of these were easily dated thanks to their close proximity to known quantities, like the New House, while others were less easily identifiable. The lack of confident dates on numerous features is a reason for more work, especially excavation, on site in the future. Lastly, I would personally encourage anybody who has not been before, to go and see this great site.

References

(1924). Proceedings at Meetings of the Royal Archaeological Institute. The Archaeological Journal 81. Royal Archaeological Institute. 315-380. (Basing House pp. 359-364).

English Heritage (last updated 2004). National Monuments Record, Basing House. at: http://archaeologydataservice.ac.uk/archsearch/record.jsf?titleId=1033242; 27 Feb. 2013.

English Heritage. (2007a). Pastscape, Basing House at: http://www.pastscape.org.uk/hob.aspx?hob_id=240444; 01 May 2013.

Wikipedia. (2013). Wenesclaus Hollar – The Siege of Basing House at: http://en.wikipedia.org/wiki/File:Wenceslaus_Hollar_-_The_Siege_of_Basing_House.jpg; 6 Mar 2013.

Wikipedia. (2013). Launceston Castle at: http://en.wikipedia.org/wiki/File:Launceston_Castle_-_geograph.org.uk_-_22242.jpg; 12 Jul 13


Filed under: Spring Survey, Student Research Post, Will Heard Tagged: building survey, gpr, gps, ground penetrating radar, leica, magnetic susceptibility, magnetometry, new house, old house, resistance survey, resistivity, survey, surveying, topographic, total station, undergraduate

Guest Blog: Will Heard – Spring 2013 Survey Results Part 1

As part of the Spring Survey that the University of Southampton students carried out this April-May, undergraduate Archaeology students who attended the fieldwork were asked to write a report summarising the survey data. One of the students that attended the Spring Survey, Will Heard, has written a summary of his report, and has kindly allowed […]

As part of the Spring Survey that the University of Southampton students carried out this April-May, undergraduate Archaeology students who attended the fieldwork were asked to write a report summarising the survey data.

One of the students that attended the Spring Survey, Will Heard, has written a summary of his report, and has kindly allowed us to share it with our readers. Will has written so much, that we’re sharing part 1 this week, and part 2 next week!

Thanks Will!

Basing House Spring Survey Part 1

Will Heard

Will Heard

by Will Heard, 2013
Will is a third year undergraduate student, with interests in survey, geophysics and the use of computers for archaeological purposes. He is interested in any period of history, having worked at Basing House and on a Bronze Age site amongst others.  He is currently working on his undergraduate dissertation, which aims to use GIS systems to reveal the theoretical effectiveness against invasion of a small section of the World War II G.H.Q Line in Essex.

Survey Summary

During March and April 2013 a topographic and geophysical survey was undertaken at Basing House by University of Southampton staff and students. Most of the topographic survey was carried out in week one between the 18th and 22nd March, while all of the geophysical survey was carried out in week two, between the 8th and 12th April. The work aimed to further the understanding of the sites layout and history by providing a computer model which will allow more detailed analysis of the landscape, and possibly help us see things our naked eyes cannot. The model will consolidate much of the smaller scale on site investigation (excavations, geophysics) which have been carried out and documented in the past. Similarly, future work of all types will be able to use the model to add onto a coherent body of knowledge. The geophysical and building survey, which was carried out alongside the topographic work, will add to this body of knowledge on Basing House.

Introducing the Site

The area has a long history with the earliest known finds dating from the Mesolithic era, although this occupation is not currently seen as continuing, since Neolithic remains are rare to nonexistent on the site (English Heritage 2004). Bronze Age flint, as well as Iron Age and Roman ceramics have also been recovered (English Heritage 2004). The most discussed period of the sites history starts in the Medieval period, with the construction of the Motte and Bailey castle (see central round and plateau like feature in figure 1) and later the Old and New Houses (inside and to the east of the motte in figure 1). The Motte and Bailey were erected sometime in the twelfth century AD and the Old and New Houses erected one after the other in the sixteenth century AD. The New House merited its own earthworks to the east of the Motte and Bailey and later, semi-circular Civil War gun platforms were added onto the earlier Medieval outer bank to the south. After the Civil War the houses were demolished, with much of the stonework taken and used in the nearby village. Other features include a dry and filled in part of the eighteenth century Basingstoke Canal (north edge of figure 1).

Figure 1 - OS Map data with a polygon overlaid (red line). The polygon represents the extent of the area surveyed topographically. ArcGIS 10.1. © Crown Copyright/database right 2013. An Ordnance Survey/EDINA supplied service.

Figure 1 – OS Map data with a polygon overlaid (red line). The polygon represents the extent of the area surveyed topographically. ArcGIS 10.1.
© Crown Copyright/database right 2013. An Ordnance Survey/EDINA supplied service.

Below, figure 2 shows the areas that were surveyed with resistivity equipment. The contours in this figure are derived from a raster.

Figure 2 - The area surveyed with resistivity equipment (contours derived from a raster). ArcGIS 10.1. © Crown Copyright/database right 2013. An Ordnance Survey/EDINA supplied service.

Figure 2 – The area surveyed with resistivity equipment (contours derived from a raster). ArcGIS 10.1.
© Crown Copyright/database right 2013. An Ordnance Survey/EDINA supplied service.

Since the survey produced one continuous area of data (see figure 3 and figure 4 below), the following pictures have some degree of overlap. The area has been split into four areas: A, B, C and D. The topographic areas B and C are the highlights included in this week’s blog post. In terms of the resistivity survey, the highlights were the Motte interior survey and the New House site survey.

Figure 3 - Basing House complete TIN with features overlain. ArcGIS 10.1

Figure 3 – Basing House complete TIN with features overlain. ArcGIS 10.1

Figure 4 - Basing House complete Raster with features overlain. ArcGIS 10.1

Figure 4 – Basing House complete Raster with features overlain. ArcGIS 10.1

Area B

Area B is the southernmost area surveyed and has the highest general elevation of any of this report’s areas. It comprises what is thought to be a long semi-circular bank that was possibly constructed at a similar time to the Motte and Bailey, as well as three Civil War raised gun platforms (English Heritage 2007a). These are clearly visible on the ground and are highlighted in figure 5. It is possible that the fact the three gun platforms are attached to the bank means that the bank was constructed earlier, since a connecting bank between Civil War gun platforms would not always be necessary. In the Civil War, the bank would have provided good cover against bombardment or assault from the south and so adding gun platforms to an already good fortification was the logical course of action. At points the ditch protecting the bank is deeper, for example at the westernmost end. Towards the southern end the ditch becomes very shallow. This variation is probably due to the natural topography, which gets higher as one goes further south on our model, this variation is highlighted in figure 6 below.

Figure 5 -  Area B TIN and Raster. ArcGIS 10.1.

Figure 5 – Area B TIN and Raster. ArcGIS 10.1.

Figure 6 - Area B 3D TIN with features added. From the east. Light from the east at 45 degrees. Vertical exaggeration at 1.5. ArcGIS 10.1.

Figure 6 – Area B 3D TIN with features added. From the east. Light from the east at 45 degrees. Vertical exaggeration at 1.5. ArcGIS 10.1.

Area C

Area C is the centre of the topographic survey area and comprises the Motte, Bailey and their respective ditches. The elevation of this area is generally quite high, while being lower than Area B (see figures 7 and 8 below).

Figure 7 - Area C TIN and Raster. ArcGIS 10.1.

Figure 7 – Area C TIN and Raster. ArcGIS 10.1.

Figure 8 - Area C 3D TIN with features added. From the west. Light coming from the east at 45 degrees. Vertical exaggeration at 1.5.

Figure 8 – Area C 3D TIN with features added. From the west. Light coming from the east at 45 degrees. Vertical exaggeration at 1.5.

The Motte and Bailey ditches are very deep, survive very well and show very nicely on the topographic models. All of the surviving cellars inside the motte lend support to Peer’s plan (figure 9 below).

Figure 9 - Plan of the Old House as excavated by Peers. After (Royal Archaeological Institute 1924: 362).

Figure 9 – Plan of the Old House as excavated by Peers.
After (Royal Archaeological Institute 1924: 362).

The variations on the east side of the bailey are caused by a previous excavation that was carried out before a bridge over the ditch was constructed. The yellow line (north side of figure 8 above) represents a raised piece of ground and is the location of a large tree.

The topographic model shows the Motte being higher than the Bailey. This is to be expected, both because the land naturally goes down northwards, but also because the Motte was where the Lord would have resided.

The form of the Motte and Bailey is very similar to other examples like Launceston Castle (figure 10 below).

Figure 10 - Launceston Castle. In size, it is smaller than Basing House. However, its Motte and Bailey design is similar. After (Wikipedia 2013)

Figure 10 – Launceston Castle. In size, it is smaller than Basing House. However, its Motte and Bailey design is similar.
After (Wikipedia 2013)

References

Anon. (1924). Proceedings at Meetings of the Royal Archaeological Institute. The Archaeological Journal 81. Royal Archaeological Institute. 315-380. (Basing House pp. 359-364).

English Heritage (last updated 2004). National Monuments Record, Basing House. at: http://archaeologydataservice.ac.uk/archsearch/record.jsf?titleId=1033242; 27 Feb. 2013.

English Heritage. (2007a). Pastscape, Basing House at: http://www.pastscape.org.uk/hob.aspx?hob_id=240444; 01 May 2013.

Wikipedia. (2013). Wenesclaus Hollar – The Siege of Basing House at: http://en.wikipedia.org/wiki/File:Wenceslaus_Hollar_-_The_Siege_of_Basing_House.jpg; 6 Mar 2013.

Wikipedia. (2013). Launceston Castle at: http://en.wikipedia.org/wiki/File:Launceston_Castle_-_geograph.org.uk_-_22242.jpg; 12 Jul 13

Next Week: Part 2

In the next post, we’ll look at the results from the Motte resistivity survey and the New House resistivity survey.


Filed under: Spring Survey, Student Research Post, Will Heard Tagged: building survey, gpr, gps, ground penetrating radar, magnetic susceptibility, magnetometry, new house, old house, resistance survey, resistivity, survey, topographic, total station, undergraduate, will-heard

Spring Survey – Week 2 Review

The undergraduates have finished working at Basing House for this Spring, and we’ll be back on site in a few weeks to collect  more data for some of our postgraduate students who are using the site for various projects. This is the team from Week 2. I can’t believe how much ground these guys covered! […]

The undergraduates have finished working at Basing House for this Spring, and we’ll be back on site in a few weeks to collect  more data for some of our postgraduate students who are using the site for various projects.

This is the team from Week 2. I can’t believe how much ground these guys covered! Thanks all!

Spring Survey – Week 2 Team

I thought it might be useful to give you a rundown on the different tools that we were using to record the site during the topographic, building and geophysical survey, as we keep saying things like ‘mag’ and ‘GPR’ without explaining what any of them are!

In our next post, we’ll begin to share the results of the surveys, so do check back regularly, or subscribe to the blog for updates, using the link on the navigation to the right.

Geophysical Survey

There are a few pieces of kit that we use for a geophysical survey.

Magnetometry

Magnetometry

Magnetic survey uses a magnetometer to identify the presence of magnetised iron oxides in the soil. Magnetometers are great for identifying ferrous oxides or burnt/ heated material that show up as ‘positive’ features, as well being great for finding negative features, like a pit or a ditch.  Magnetometers are great for identifying industrial areas, and buildings.

The magnetometer you see in these photos is a Fluxgate Gradiometer, which is the most commonly used type in the UK. With this instrument, we take two readings at a time.  The vertical poles on either end of the horizontal handle are the sensor-sets. Within each of the poles there are two sensors, one at the top and one at the bottom. The reading that we are measuring is the difference between the top sensor and the bottom sensor. The fluxgate sensors are always a set distance apart, normally half a metre or a metre (in this instrument, they are a metre apart).

The sensors are very sensitive and so when you are using one, you must be careful not to be wearing anything metal. As you can see from the photograph below, this often makes attire a bit unusual. Tracksuit trousers are the best option, and cheap wellies work well for footwear. Belts are an absolute no-no, and raincoats with lots of zips and poppers must be avoided. The higher up your body the metal is, the less likely it is to affect the instrument. So piercings and glasses with metal frames are sometimes okay, but ideally, should be removed.

The person operating the instrument will walk up and down in a grid of between 10-30 metres. Each grid is marked out on the ground, normally using bamboo canes placed at intervals (every two metres is a good way to do it), and the person carrying the instrument can use these canes as markers to aim for to ensure their line is aligned correctly within the grid.  You can collect the data by walking parallel lines, or in a zigzag shape.

Magnetometry – note the poncho – a coat with no metal in it is hard to find!

Magnetic Susceptibility

Magnetic Susceptibility

Magnetic susceptibility is possible because material can become temporarily magnetised: Any human activity will affect soil magnetic susceptibility. Ideally what we’re searching for is topsoil that has been affected by features buried underneath it.  Magnetic Susceptibility can be collected in continuous or single measurements. The instrument sends out a magnetic pulse, and measures the ability of the soil to hold a magnetic charge.  Human activity affects the chemical makeup of the soil, so magnetic susceptibility will be affected by this, and can be used to pick up on things like areas of a settlement where there has been lots of rubbish deposited or farming activity taking place.

To the right of this photograph, Crystal is holding the GPS; more about that piece of kit later in this post…

Resistance Survey

Resistance survey

Resistance survey works by feeding an electric current into the soil.  Sub-surface materials all have varying resistivities to an electrical current. With this technique, we measure these values, and in so doing can build up a picture of what is under the surface. Generally walls and other positive features such as trackways, cists, rubble and man-made surfaces result in high resistance, and negative features such as ditches, drains, graves, and pits result in low resistance. This is because negative features tend to have higher moisture content.

Depending upon the material and the water content, features can show up as either positive or negative. Typically stone features are high resistance, whereas ditches, depending upon their fill are negative (or low) resistance. The resistance of materials under the ground uses the ability of soil to let electric current pass through it, and this is related to the interstitial water (i.e. water in the gaps in-between) and salts within the soil.

On the last day of the survey, we had to abandon the resistance survey because there was the chance of the results being ruined by the heavy rain, and standing water.

Ground Penetrating Radar (GPR)

Ground Penetrating Radar

Ground Penetrating Radar works by firing radar pulses into the ground and recording the speed at which the signals are reflected back to the device.  These varying reflections allow a picture to be built up of the sub surface topography. GPR data are recorded in traverses, but are then joined together and sliced to produce flat layers, each layer representing measurements at a particular depth. These layers are known as time slices and can be ‘stacked up’ to provide a 3D model of the subsurface topography.  GPR is particularly good at detecting brick or stone foundations and is especially useful as it provides relative depth measurements.

Building Survey

Total Station with red laser

Total Station

In the photograph above, Dan is using a using a Total Station to carry out a building survey of the Old House.  There are two ways to use a Total Station to survey standing remains.

The total station is an electronic theodolite, which has an electronic distance meter which measure the distance and angles from the total station to a particular point. A laser is used to make this measurement. The total station sends out a beam which can either meet the surface that is being recorded, showing up as a red light (as is in the photographs above and below) or can meet with a target in the form of a prism, mounted on a staff of a fixed height.

In the first method, the building remains themselves are the target, and point by point the shape of the walls and features are recorded by the total station operator. For the Old House, the teams began with the top and bottom edges of the brickwork, and then surveyed in additional features, such as the bread ovens, doors and window frames.

Total Station with TheoLT – seeing the data live

Topographic Survey

Total Station with prism

The alternative method, involves using the machine on the tripod as a base station.  This is for the recording of changes in landscape. The total station remains in the same place, and a prism (see the photograph below) is used as a target.  The prism is moved around the site, and at each point where there is a significant change in topography (or at regular intervals, of around 5 metres) the total station operator matches the laser from the total station to the target prism and records the point.

Survey Prisms

When carrying out a survey on a site the size of Basing House, its good practice to set up base stations across the site.  We initially had fourteen base stations, which we added at the beginning of the survey. But the students had to add more, in order to record more problematic areas of the site. For instance, the ditch around the motte and bailey was hard to record without adding lots of stations all of the way round, in order for each base station to ‘see’ back to the previous station, and on to the next one.

Below, Dom is using the GPS to log a base station before we began the survey on site. Chris and Tim are adding wooden pegs in the spot that the GPS is recording; this becomes the base station.

Setting out the base stations with a total station

Global Positioning System (GPS)

A GPS uses the NAVSTAR GPS, which is a system which uses a collection of 24 satellites, controlled by the US Department of Defence, which are orbiting the earth. The GPS communicates via a signal with the satellites using a radio receiver, to work out its geographical position – this is possible because the GPS can compute the distance from the satellite by multiplying the velocity with the time the signals take to transmit from the satellite. The more satellites in range of the GPS, the better. The GPS needs a minimum of three satellites to be able to tell where it is on a horizontal plane, and at least four satellites to calculate where it is 3-dimensionally; i.e. the latitude, the longitude and the height.

Global Positioning System (GPS)

At Basing House, we used the GPS as described above; as a positioning tool, to tell us where something was; we used it both for the magnetic susceptibility data, and also for adding the base stations. But GPS can also be used as a surveying tool. In the photograph above, Lizzie is using the GPS to survey in the gatehouse of the Old House. The GPS can record the location of a series of points, so we used it to fill in gaps of the topographic survey, and the building survey. In the photograph below, you can see some of the points that we recorded up on the Bailey. I walked up and down in a grid, and took points at regular intervals, to build up a record of the topography of the Bailey.

GPS screen

Finding out more about Geophysics

I used Gaffney, C., Gater, J. (2006). Revealing the Buried Past: Geophysics for Archaeologists, The History Press: Stroud to write this blog post (my geophysics is a bit rusty and I wanted to make sure the iformation was up to date!). I really do recommend this book if you want to find out more about Geophysics prospection for archaeology.

The Archaeological Prospection Service at Southampton (APSS) website – http://www.southampton.ac.uk/archaeology/apss/ -  is also a great place to read about geophysics. Kris Strutt writes an excellent blog – http://kdstrutt.wordpress.com/ - which covers some of the work that he does with the APSS, so follow his posts to keep up to date with the projects that the team is involved in.


Filed under: Spring Survey, Survey Equipment Tagged: equipment, geophysics, global positioning system, gpr, gps, ground penetrating radar, leica, magnetic susceptibility, magnetometry, prism, resistivity, satellites, theolt, topographic, total station

Basing House Survey Final Day – A rain check and some reflections

Reblogged from Kristian Strutt: The second week of survey at Basing House finished on Friday in a spray of mud and rain, hailstones and inky cloud. What had promised to be a reasonable day quickly became unworkable, wet and cold. The teams set out for the final day of survey, focusing on completion of the […]

Reblogged from Kristian Strutt:

Click to visit the original post
  • Click to visit the original post
  • Click to visit the original post
  • Click to visit the original post
  • Click to visit the original post
  • Click to visit the original post

The second week of survey at Basing House finished on Friday in a spray of mud and rain, hailstones and inky cloud. What had promised to be a reasonable day quickly became unworkable, wet and cold. The teams set out for the final day of survey, focusing on completion of the magnetometry and resistivity in the area of the New House and outer bailey, and GPR over the outer bailey also.

Read more… 460 more words

Kris Strutt's blog on Day Five of the Week Two geophysics work at Basing House.

Basing House Spring Survey – Week 2 Day One

After a few weeks out of the field, the staff and students from the University of Southampton arrived back at Basing House to start the geophysical survey component of the fieldwork. A mix of third year students from Archaeology and … Continue reading

After a few weeks out of the field, the staff and students from the University of Southampton arrived back at Basing House to start the geophysical survey component of the fieldwork. A mix of third year students from Archaeology and Oceanography, Erasmus students and postgraduates headed out to the site. Chris Elmer again gave the group a tour of the site, while supervisors commenced gridding out the site using Smartnet GPS. The group were then divided into teams to carry out magnetometry, resistance survey, GPR and magnetic susceptibility.

Team gridding out the site with the GPS

Team gridding out the site with the GPS

Magnetometry commenced in the area to the west and south of the ringwork and Old House, covering parts of the Civil War defences. Two Bartington Instruments gradiometers were used. The resistivity teams started work in the area of the Outer Bailey, surveying at 0.5m by 0.5m resolution.

Magntometer survey across the Civil War defences

Magntometer survey across the Civil War defences

Resistance survey in progress

Resistance survey in progress

One team also got to grips with a survey of the Old House using a 200Mhz GPR . The aim with this is to map the remaining buied walls and rooms of the Old House, some of which run to a depth of 5-6m below the modern ground surface.

GPR survey in the Old House

GPR survey in the Old House

Results from the first day of work indicate possible Iron Age and Romano-British remains in the magnetometry, together with the clear line of the Civil War earthworks, and structures in the resistance and GPR survey. It is early days so far, but in the coming days more news on the project will be posted here and at basinghousecat.wordpress.com!


Spring Survey Week One – Day Four

Reblogged from Basing House CAT Project: Today was a cold but very productive day up at Basing House. The student teams are getting faster at recording topography and have covered huge areas of the site. Surveying in the limits of … Continue reading

Reblogged from Basing House CAT Project:

Click to visit the original post
  • Click to visit the original post
  • Click to visit the original post
  • Click to visit the original post
  • Click to visit the original post
  • Click to visit the original post
  • Click to visit the original post
  • Click to visit the original post
  • Click to visit the original post
  • Click to visit the original post
  • Click to visit the original post
  • Click to visit the original post
  • Click to visit the original post
  • Click to visit the original post
  • Click to visit the original post

Today was a cold but very productive day up at Basing House.

The student teams are getting faster at recording topography and have covered huge areas of the site.

Surveying in the limits of the New House has been tricky as there are partial walls to try to identify.

One of the student teams is made up of Masters students, two of whom are planning to use Basing House as the major case study for their dissertation projects.

Read more… 892 more words

Today's blog from Nicole for the survey at Basing House!