Ancient earthworks, burial mounds and habitation sites, roadways and even Civil War emplacements are just some of the features than can potentially be revealed using LiDAR (Light Detection and Ranging). This is an air-borne laser technology that uses laser beams to detect and measure accurately physical features on the ground, even those obscured by trees and undergrowth.
Glos Arch’s (formerly GADARG)
"SEEING THROUGH THE TREES" PROJECT
A report has now been published describing the eight site investigations carried out between May 2009 and June 2010, based on the LiDAR data produced by Cranham Local History Society's survey in 2008. The project was made possible by a generous grant awarded to GADARG under the National Lottery "Awards for All" scheme, enabling us to meet all the costs of producing the LiDAR images, printing the report and purchasing a range of surveying and other supporting equipment. The report was presented to 'Awards for All' at the end of August 2010. Copies of the report covering the first year's works have been distributed to GADARG members as a Glevensis-style monograph publication.
The grant paid for the raw LIDAR data to be processed (by the County Archaeological Service), for the equipment needed to assess the evidence on the ground and provided training for volunteers. The project provides opportunities for hands-on experience in interpreting the LIDAR images and recognising and recording potentially interesting sites on the ground through a range of activities such as field-walking, geophysics and earthwork surveying and, for those less keen on the outdoor aspects, through documentary research. Training and supervision is provided in all the techniques required.
Over the first year of the project, 69 people were variously involved in its activities. Of this number, 36 were GADARG members, 9 were new to the Group, 9 were from several different local history societies and there were representives from the National Trust and Gloucestershire County Council Archaeology Service.
Anyone interested in being part of this new and exciting initiative and wishing more information is invited to contact a committee member.
This is a powerful archaeological procedure to systematically sample the upper surface of cultivated or disturbed ground, in an effort to locate or map the distribution and extent of archaeological sites. The basic assumption is made that the topsoil contains distinctive traces of archaeological activity deposited onto or into the topsoil from above, for example waste from an episode of flint knapping by someone sitting on the ground and also material from features underneath the topsoil that are exposed to the effects of cultivation or ground works and therefore mechanically brought into the ploughsoil. Cultivation will have mixed all these different sources of material together, and a proportion of what is in the soil will be visible on the surface.
Conventionally, fieldwalking in grids or along lines called transects has formed the backbone of archaeological survey fieldwork, at least where visibility is fairly good. A single researcher or team will walk slowly through the target area looking for artefacts or other archaeological indicators on the surface, often recording aspects of the environment at the time. The method works best on either ploughed ground or surfaces with little vegetation. On ploughed surfaces, as the soil is turned regularly artefacts will move to the top. Erosion and soil loss on uncultivated and lightly vegetated soil (e.g., in semi-arid environments) may also cause artefacts to 'rise' to the surface.
Linton Farm, Highnam , Gloucester (see Glevensis 44 & 45, Newsletter 131 in Publications)
Sherborne Estate, Gloucestershire (2011, 2013)
Excavation is part of what the Group does, but a lot of research work is put in before actually getting down to digging. There has to be prior evidence and this is obtained by various means, particularly geophysics, aerial photography and fieldwalking. If the site can be identified in local records, so much the better.
Gadarg at Gloucester City Centre Community Partnership’s Greyfriars dig (see Newsletter 131 in Publications)
Excavations in the Crypt Schoolroom, Southgate st , Gloucester
Using the Resistivity Meter
Fieldwalking in progress
Resistivity measurements are made using a resistivity meter connected to sensing electrodes to measure the electrical resistance of the ground sub-surface, which varies according to moisture content. A low level electrical current is passed through the soil between two sensing electrodes and two reference electrodes placed on the ground and the resistance is measured and expressed in units of ohms. The data in the resistivity meter is processed on a computer to produce an image of the results typically on a greyscale plot. Lower resistance readings, which measure darker on the survey plots, indicate damper areas such as ditches, whilst higher resistance appears lighter and implies the presence of solid material e.g. stone walls or made up path. The measurements are usually taken at 1m intervals along a series of parallel traverses 1m apart.
Carrying out the survey entails measuring out the (nominally) 20m grid squares with tapes and then walking up and down each square, touching the ground with the electrodes whilst automatically recording the readings digitally in the resistance meter memory. It is a non-intrusive technique commonly used on historic sites to record buried archaeology and does not therefore entail the necessity for any digging on the survey site.
Sherborne, Gloucestershire - Lost Medieval Church (ongoing)
Chapel Hay, Churchdown - Burial Ground (see Newsletter 132) in Publications
Kingsholm: History on your Doorstep Project (Heritage Lottery Funded), Gloucester – Investigations into Roman Gloucester and the search for the Fort and Anglo Saxon Royal Palace. (see Newsletter 132) in Publications
That's when the hard work begins. Sometimes it's necessary to go deep to recover evidence of early periods - as much as 4 metres in the centre of Gloucester, but much less on the Cotswolds where ploughing is already destroying valuable evidence. Working on a 'dig' is a very sociable activity. It can be an odd mix - hard shovelling to careful trowelling, painstakingly recovering fragile pieces of glass or pottery; of course as work proceeds the features revealed are carefully recorded, drawn and photographed. Then follows the work of analysing the structural evidence, documenting, identifying and analysing finds and finally of publishing a detailed report.
Click here for the latest ‘digging’ information