Light Detection And Ranging (LiDAR) surveys are one of our Woodland Heritage Services
The woodlands of ‘The Blean’ in Kent, lay to the west of the city of Canterbury. This historic city and earlier settlements have left their marks on the surrounding landscape and the area of The Blean include known features such as The Pilgrim’s Way and Bigbury Hillfort (reputed to be the site of Caesar’s first battle on British soil).
Whilst the route of The Pilgrim’s Way is well recorded and many of Bigbury’s ramparts mapped, the woodland cover over parts of the hillfort and elsewhere in The Blean means that there are many unrecorded or unmapped components of the historic environment. The results from the LiDAR survey are therefore significantly adding to an understanding of the evolution of this famous city.
One of the most striking features seen in the LiDAR images are the ancient drove ways which cut across the landscape. Some of these are well-known and occur on existing maps. But what is evident from the lidar images, is the unusually sinuous nature of some of them, raising questions about their origins.
Other potential archaeological sites have also been discovered, ranging from charcoal hearths, just a few metres in diameter, to large boundary earthworks and enclosures. One of these larger features, of uncertain function, encloses a hilltop to the north of Bigbury and at first glance resembles a potential hillfort. Whilst the exact nature of this feature is still being clarified, if it is of Romano-British date, it could greatly alter the history of the battle of Bigbury.
The management of individual trees also has a long association with the county of Kent, with many areas historically allocated to coppicing (especially sweet chestnut) and fruit trees (especially orchards). The vegetation height data, which can be derived from the lidar, helps to provide an accurate map of the size and distribution of many of these areas which are still traditionally managed.
Surface model of Bigbury Hillfort
- Terrain model of Bigbury Hillfort
Vegetation heights over Bigbury Hillfort
Show the Radfall hidden beneath the trees
- Show the Radfall running N-S
Following on from the 2009 survey of the southern and eastern parts of the Weald Forest Ridge, the western and central parts were captured during 2010 to complete the survey. By far the most prominent feature in the landscape is that of the Forest Ridge itself, forming a spine of higher ground running in an east-west direction, incised in a few locations by natural water channels.
Of archaeological features shown in the LiDAR data of the central area (Ashdown Forest), pillow mounds, braided tracks and charcoal hearths are common. Additionally, several well-defined circular earthworks are evident, many metres in diameter. Whilst their exact function is still to be confirmed, it is possible that they show the locations of former ornamental plantings, creating clumps of trees in prominent locations in the landscape.
Heading further west, mineral extraction becomes more evident, varying from large areas of densely packed, bell pits, to more widely dispersed, but larger individual quarries.
Show surface model of the Minepits
- Show terrain model of the Minepits
Surface model of Wakehurst Place
- Vegetation heights at Wakehurst Place
‘Pillow Mounds’ on Ashdown Forest
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‘Braided Tracks’ on Ashdown Forest
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Many individual quarries in fields north of Wakehurst
Motte and Bailey,
Circular features and smaller platforms,
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Wilsontown was the second of the lowland coke-fired ironworks to be built in Scotland (after Carron Ironworks in 1759). It can be set into the wider context of the Industrial Revolution by comparison with the initial expansion of coke-fuelled ironmaking at Coalbrookdale, Shropshire (1754) and the foundation of the great Welsh ironworks of Cyfarthfa (1765) and Dowlais (1759). The much-ruined remains were demolished in 1974. However, many of the early features of the ironworks remain visible, including the blast furnaces, forge, coke and lime kilns – and an extensive area of bell pitting.
In order to inform future conservation management of this historic site, Forestry Commission Scotland decided to acquire LiDAR data for planning and interpretative use. Images produced from this detailed topographic survey showed that despite the ironworks being largely reduced to foundations, the plans of many buildings can still be traced. For example, two blast furnaces, a forge and other buildings can be seen either side of the river (bottom left of image). Further north, to the east of the river, the foundations of several rows of workers' cottages (as well as ruins of a later terrace of houses) are visible. Surrounding the site are the remains of some 70 bell pits covering the hillside to the east of the works, interlinked by tramways.
Surface model of Wilsontown Ironworks
View animation of Wilsontown Ironworks
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Culbin Sands is an area of Scottish coast, located to the east of Inverness and on the northern edge of the Forestry Commission managed, Culbin Forest.
During the Second World War, hundreds of wooden posts were driven into the coastal sands to create a physical barrier, preventing enemy gliders from landing. Today, many of these posts have rotted away completely and those remaining are often variable in height and condition. In an attempt to record those remaining before they are lost to the elements, a LiDAR survey of the coastal area was commissioned with survey parameters specifically designed to ensure that each upstanding post would be recorded.
Remaining anti-glider posts mapped by LiDAR
Remaining anti-glider posts mapped by LiDAR
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When LiDAR data are captured, in addition to the system recording the time taken for the reflected signal (equating to changes in elevation), the intensity of the reflection can also be recorded. Whilst there are several factors which can influence this signal intensity, such as the colour and texture of the surface struck by the laser, for non-vegetated soils, changes in the moisture content can also be discernable.
An example of this can be seen in the 2 images of Culbin Sands below, where one image shows only changes in elevation (increasing from the dark blue, through the paler blue, green, yellow to reds) and the second image also shows the intensity data as shades of grey/black. This second image clearly shows a greater level of detail within the sands.
Changes in elevation,
Changes in elevation with additional intensity information, Culbin Sands
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Salcey Forest is a mixed community forest in Northamptonshire. The lidar survey of the forest clearly revealed the extensive drainage systems in use throughout the forest. Two roughly circular features of unknown date are very evident in the southwest part of the forest. The image is coloured to show changes in elevation. A slope analysis was also applied to enhance the detail of the drains and ditches.
Terrain model of SW Salcey Forest
Three lidar surveys of Alice Holt Forest have been undertaken in conjunction with the University of Cambridge. These surveys were completed in November 2006, August 2009 and March 2010. The mild autumn in 2006 meant that both of the initial surveys were effectively leaf-on surveys whilst the March 2010 was captured before the forest canopy opened. By comparing the vegetation height between the years, it is possible to map vertical changes within the forest.
The first image below shows the height of the forest and where the tallest trees are found through the centre of the forest and some strips of trees have been from the south west section.
The second image shows change over the four year period, with blues and greens showing increase, whilst yellows, reds and browns show a decrease. The red/brown areas in this second image show where trees have been removed from the southern edge and along some of the rides. The darker blues equate to the regions of higher growth. Several of these high growth areas correspond to the previously harvested regions, now dominated by younger vegetation to the southwest, indicating their higher rate of growth.
Map of forest vegetation coloured to show changes with height
Changes in forest vegetation height between the surveys