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The field system of Chapperton Down lies within the Salisbury Plain Training Area on Salisbury Plain and is a Scheduled Ancient Monument. The aim of the periodic resurvey is to monitor any erosion and damage to the upstanding earthworks to assist in the ongoing management of the site.
Wessex Archaeology were commissioned by Landmarc Support Services to undertake the original baseline survey then undertake periodic repeat surveys to assess any change.
A progression of methodologies
The original baseline topographic survey was undertaken in 2005 using direct survey techniques, namely the use of a survey grade Global Navigation Satellite System (GNSS) capable of recording to centimetric precision. The speed with which data could be captured using the GNSS as opposed to the use of a Total Station Theodolite (TST) had significant advantages due to restricted access to the site.
Fieldwork involved walking transects across the site at fixed intervals to gather height information as well as surveying breaks of slope and any specific impacts observed. This data was then imported into a Geographic Information System (GIS) for analysis and reporting involving the creation of a Digital Terrain Model (DTM) for the site.
The first resurvey in 2007 repeated this methodology but also included some comparative work using the GIS to look for change between the resurvey and the baseline data. The GIS is an ideal tool for undertaking surface difference analysis and producing maps to illustrate the situation as observed on the ground.
In 2009, the resurvey was undertaken using Terrestrial Laser Scanning (TLS) which allowed much more surface detail to be captured. Fieldwork time was reduced considerably, a significant benefit given the restricted access to the military land.
Conclusions
TLS is not just used for recording buildings and upstanding earthworks, it can provide a rapid and high quality technique for undertaking topographic survey across wider areas of landscape. When compared to other suitable methods such as GNSS or TST, it can provide equivalent or better quality of data in terms of accuracy, with much higher resolution and reduced fieldwork time.