Fingle Woods and Castle Drogo Aerial Survey Analysis and Interpretation Project – LiDAR interpretation

Archaeogeomancy: Digital Heritage Specialists – archaeological geomatics – the majick of spatial data in archaeology – archaeological information systems for the digital age:

 

Prestonbury Castle, one of the best of the iron age hillforts that ring the edge of Dartmoor

Prestonbury Castle, one of the best of the iron age hillforts that ring the edge of Dartmoor

Archaeogeomancy are very pleased to have completed this catchily named project for the National Trust (NT). The project involved working with LiDAR data produced by Bluesky in order to enhance the Historic Environment Records (HER) resources for the NT property and also produce some informative 3D visualisations of key monuments.

To this end, a team was put together by Archaeogeomancy comprising experts in spatial analysis and archaeologists with considerable experience and specialist training (provided by English Heritage’s aerial survey team) in aerial survey transcription and LiDAR work. All transcription work was carried out using the guidelines produced for the National Mapping Programme (NMP) so as to ensure a high standard of output compatible with all other NMP activities.

The project was able to enhance 41 features already recorded in the HER including hillforts, pillow mounds, charcoal burning platforms/hearths, and quarries. In addition, 90 new sites were identified, all within areas of woodland and previously unmapped.

As has previously been demonstrated (see for example the work of Peter Crow at the Forestry Commission), the use of filtered LiDAR data for investigation of wooded areas works well. This project did not make use of any specialised filtering processes but instead used filtered data as provided by a commercial operator. This goes to show how much progress has been made with regard to the kinds of filtering undertaken as only a few years ago, much commercially available filtered LiDAR data was less useful for archaeological work due to the filtering process removing too many of the archaeological features of interest.

Unfortunately, investigation of the intensity component of the LiDAR, which can often reveal so much additional information not present in the elevation data, suggested that for this Study Area, little was to be gained from a detailed analysis. Unlike previous work eg on the Somerset Levels where the intensity data was an incredibly useful resource for spotting subsurface features, in this case, the intensity data was uniformly uninformative due largely to the nature of the ground surface and vegetation cover.

Cartographic output for Prestonbury Castle showing location, PCA and Slope as well as the transcribed features

Cartographic output for Prestonbury Castle showing location, PCA and Slope as well as the transcribed features

The usual range of digital products were output including vector transcriptions as lines/polygons, raster derived products such as slope, hillshades and Principal Components Analysis (PCA) plots. A full report including an A3 map for each site was produced for the NT and HERs. In addition, some interactive 3D visualisations were produced.

Acknowledgements

Thanks to James Parry of the National Trust. Thanks also to Vicki Lambert, Andrea Hamel, Richard Milwain and Nick Cooke of Wessex Archaeology.

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