Using radar to reveal hidden archaeology

Undertaking ground penerating radar survey at Tattershall Castle

When most people think of archaeologists they picture people scraping at the ground with their trowels. In reality an archaeologist’s toolbox is much more varied and we often use lots of scientific and technological techniques to undertake non-intrusive surveys of our archaeological sites. These methods allow us to investigate subsurface deposits without destroying any of the precious archaeology lying beneath.

What is Ground Penetrating Radar?

Ground penetrating radar (GPR) is a geophysical method that uses radar pulses to detect and map subsurface archaeological features and is particularly suitable for investigating sites of known demolished stone structures. The way it works is to measure the time it takes for the radar pulses to strike any subsurface features and reflect back; the longer the travel time the deeper the feature.

Looking for below-ground evidence of the former mansion at Clumber using GPR survey
Undertaking ground penerating radar survey at Clumber Park
Looking for below-ground evidence of the former mansion at Clumber using GPR survey

Clumber Park’s lost house

Nottinghamshire’s Clumber Park was once the country estate of the Dukes of Newcastle. The estate was enclosed as a hunting park in the 18th century and the family built a grand mansion at its centre. If you visit Clumber today sadly you would not see this once magnificent house as it was mostly demolished in 1938. This was partly due to fire damage but mainly because the family could not afford the taxes and expense that the upkeep of such a large house required.

Clumber House prior to its demolition
Historic image of Clumber House prior to it being demolished
Clumber House prior to its demolition

During the 1970s the mansion site was partially excavated, and this revealed that some of wall foundations, and tops of the cellars, were still present below the grass. Using the results of the dig the former footprint of the house was marked out with stone flags but many questions remained about how well the below-ground remains of the house survived across the full extent of the mansion site.

The mansion site during the hot summer of 2018. Note the house’s outline marked out by stone flags, and the lost rooms and corridors of the house revealing themselves as parchmarks
The former house at Clumber Park showing as parchmarks
The mansion site during the hot summer of 2018. Note the house’s outline marked out by stone flags, and the lost rooms and corridors of the house revealing themselves as parchmarks

In 2018 we commissioned Magnitude Surveys to conduct a GPR survey to assess the sub surface remains of Clumber House as well as elements of its formal terraced gardens to the east and south.

Overall, the method proved effective with good signal and penetration depth of up to c.2.5m below the present ground surface. A multitude of responses were identified which corresponded with a c.1879 plan of Clumber House. Linear features were identified corresponding to former wall locations. Gaps between these probable wall features likely represent the corridors of the mansion, and spreads of material have been highlighted and what would have been the room spaces. The mixed material within the former rooms is likely associated with the levelling of land in the location of the former building, however some of it may relate to demolition rubble after the 1938 fire which destroyed the mansion.

The survey also worked well over the former gardens and for both the eastern and southern Parterre areas, the garden layout can be determined along with walls, flower-bed edges, drains and paths.

The GPR results from Clumber showing strong wall signals against the 1879 historic house plan. Red = Grand Hall; Brown = Small Dining Room; Purple = Library; Orange = Staircase; Blue = Photographic Room; Green = Kitchen
GPR survey results of the Clumber House site
The GPR results from Clumber showing strong wall signals against the 1879 historic house plan. Red = Grand Hall; Brown = Small Dining Room; Purple = Library; Orange = Staircase; Blue = Photographic Room; Green = Kitchen

Tattershall Castle’s Medieval College

In 2019 Magnitude Surveys did another GPR survey for us, this time to assess whether any below-ground remains survive of the medieval college at Tattershall Castle in Lincolnshire. The college was once part of a larger 15th-century castle and church complex at Tattershall, founded by Lord Cromwell, and was a communal residence of secular priests or clerics associated with a medieval grammar school.

Unfortunately, we don’t know exactly when the college buildings at Tattershall were demolished and the site is now partly located underneath a modern bowling green and club house. Archaeological excavations by Laurence Keen during the 1960s revealed some of the building’s foundations still survived below the ground, along with clusters of medieval pottery.

The GPR survey was again successful and confirmed that elements of the college floor layout and foundations continue to survive below the ground. The survey detected numerous long linear wall-like responses that correlate and expand upon the plan of the college building produced from the 1960s excavations. In addition, a number of exciting small details were also interpreted by the archaeologists including a possible entrance to the college in the north-west corner of the building, an internal doorway in the southern building, a turret as well as a possible outside courtyard area.

GPR results showing signals of the surviving elements of the medieval college against the 196s excavation plan. Red = walls; Orange = possible wall; Brown = buried ground surfaces; Blue = unknown feature; Purple = modern feature (i.e. service drain)
GPR survey results of the medieval college site at Tattershall Castle
GPR results showing signals of the surviving elements of the medieval college against the 196s excavation plan. Red = walls; Orange = possible wall; Brown = buried ground surfaces; Blue = unknown feature; Purple = modern feature (i.e. service drain)