11 June 2021• Tool kit

Palaeoenvironmental Research

News Letter

Introduction

Information on the nature, timing and rates of past environmental change provides a valuable long term perspective for understanding current and future impacts of climate change. Physical, chemical and biological analysis of sedimentary archives help us to build up a picture of both regional climatic variability and local environmental change. The CHERISH project is focusing on sediment sequences which have the potential to provide records of past storm activity, extending back over thousands of years, such as coastal peat bogs, back-barrier lagoons and dune systems.

Palaeoenvironmental Sampling

Radiocarbon dating is based on the principle that all living organisms absorb carbon dioxide during their lifetime, and that after death, a proportion of that carbon which is radioactive (radiocarbon or 14C), decays at a constant rate. By measuring the amount of 14C remaining in plant material, shells or bone, an estimate how long ago that organism was alive can be made. Radiocarbon dating is generally suitable for samples ranging from a few hundred years old up to 50,000 years old, ideally suited to the timeframe under consideration by the CHERISH Project. Advances in analytical techniques mean that very small samples containing as little as 2 mg of carbon can be dated, and it is the most widely used chronological method in palaeoenvironmental studies. Variation in the temporal production of 14C, variance of the proportion of 14C in natural systems, the recycling of “old carbon” by organisms and contamination with younger or older material are all possible sources of error. Therefore it is preferable to date organic material that can be identified such as charcoal, wood and terrestrial plant material, which represent the best choice for 14C analysis of sediments.

Optically Stimulated Luminescence (OSL) Dating

OSL dating utilises the ability of naturally occurring radiation (uranium, thorium and potassium) can get trapped within the crystalline structure of minerals such as quartz and feldspar. The radiation builds up whist the mineral grains are buried in the ground, but released when exposed to sunlight. Samples protected from exposure to daylight are stimulated in the laboratory with light of a particular wavelength to release the stored radiation in the form of light, and by measuring the brightness an estimate can be made as to time the grains were last exposed to sunlight prior to burial. The Aberystwyth Luminescence Research Laboratory (ALRL) in the Department of Geography and Earth Sciences at Aberystwyth University is a world leader in the development and application of luminescence dating methods in environmental and archaeological research.

Other Activities

11 June 2021• Tool kit

Geophysical Survey

News Letter

Introduction

For many of the archaeological sites and monuments on land within the CHERISH project, what you see on the surface in the forms of walls and earthwork structures is only half the story. For many monuments there are buried features, including wall foundations and ditches, beneath the surface of the soil which represent the full extent of an archaeological site. To discover these features, we could excavate the complete monument, but this would be costly and, as excavation is a destructive process, we want to make sure that it is only used in specific circumstances.

Like a doctor who can use a range of technologies, such as X-Rays, MRI scanners or ultrasound, to peer inside us to diagnose our ailments, archaeologists can use a range of geophysical survey techniques to look beneath the surface of the soil and identify buried archaeology. Geophysical survey is a general term for a range of non-invasive or non-destructive techniques that can be used to detect features buried beneath the surface without digging.

A range of approaches exists, using specialist equipment to measure variations in the physical properties below the surface and identify archaeological features. Depending on the type of survey being conducted, structural building elements, traces of human activity or artefacts can be identified as they return significant anomalies in the data from the background values of the surrounding soil. Archaeologists can use a series of complementary techniques each enabling the measurement of a different property of the soil and potentially identify archaeological features.

Electrical Resistance

Electrical resistance is an active geophysical technique (electrical current is passed through the soil) and relies on the principle that subsurface archaeological features display different electrical properties to those of the surrounding soil. The technique measures the electrical resistance presented by buried features to the flow of an electrical current. Areas which can potentially contain more moisture, such as pits, ditches and organic deposits tend to display a lower electrical resistance as water is a good electrical conductor. In contrast, building foundations and walls, composed of more compacted less porous and permeable materials, normally have a lower moisture content than the surrounding soils and tend to show a higher electrical resistance. These contrasts, where they exist, enable subsurface archaeological features to be detected and mapped. Depending upon the electrical resistance method used, archaeology to a depth of around 0.5–1.0m can be identified.

Electrical resistance surveys are normally carried out using a series of four stainless steel probes which are inserted into the ground. Two of these probes (remote probe) are mounted on a rigid frame 50cm apart, and are systematically walked across the site using similar grids as described above and placed into contact with the ground, recording the local electrical resistance at that spot. A second set of steel probes (fixed) is connected to the frame through a trailing cable and provides the reference or background electrical resistance of the site. This method is somewhat slower than magnetometry but can complement this approach especially in the identification of buried masonry and stone features.

Magnetic gradiometry

Magnetometry is a passive geophysical technique (i.e. no energy is passed through the soil) and relies on the fact that some minerals, either naturally occurring or produced as a result of human activity, may have magnetic properties. This difference in magnetism can be caused by features such as silted up ditches, burnt areas or hearths, in-filled pits or post holes, walls and other buried remains. The magnetism of these buried archaeological features and objects is very small compared to the natural background magnetic field of the Earth and cause small localised distortions, or anomalies, in the Earth’s magnetic field and can be detected by a sensitive devices known as magnetic gradiometers.

Magnetic gradiometers come in different shapes and sizes, but most consist of a tube detector which measures the variation in magnetic signature below the soil from that of the natural background variation caused by the Earth. These devices are walked systematically across the area you wish to investigate, providing continuously logged measurements of any subsurface remains, with the hope of discovering buried archaeological features. As magnetometers are very sensitive to ferrous metals, operators must ensure that they have no metal on their bodies or clothing which could affect the results

Within the project we are using two different magnetometer devices to find buried archaeological features. The first device which is the standard for many archaeological geophysical surveys is the Bartington magnetic gradiometer. This looks like a pair of rugby posts and consists of two sensors one metre apart which is walked by a surveyor across the archaeological site within systematically laid out grids, often 20m square. Our new device, the Sensys MXPDA, consist of five sensors which are mounted either 50cm or 25cm apart on a cart system with built in GNSS. The Sensys cart system allows for much faster data collection and for greater areas of survey to be carried out within the CHERISH project areas.

Ground Penetrating Radar (GPR)

GPR is a non-destructive technique that fires pulses of electromagnetic energy in the form of high-frequency radio waves into the ground. These radio waves, similar to those used to detect aeroplanes in the sky, are pulsed into the ground surface with a high velocity and the resulting echo is reflected back off different features or layer contacts and they are finally detected back on the surface by a receiver. As the GPR waves propagate though different materials on their way to buried objects their velocity will significantly change depending upon the variable physical and chemical properties of the materials though which the waves are travelling. The reflected waves are collected by the receiving antenna and converted into a radargram, or image of the subsurface structure. Once the surface topography is applied to the data, the radargram reveals the nature and shape of the features that lie beneath the ground

GPR is widely used in archaeology and geomorphology, with a high spatial resolution and a relatively fast survey time. The data is processed with specialised computer software to generate accurate 3D maps and images of the buried archaeological structures and geomorphological structures

There are several other geophysical survey methods, including Electromagnetic Induction methods (EMI), Electrical Resistivity Imaging (ERI), and Magnetic Susceptibility Survey, which can be used independently or complement Magnetometry or Electrical Resistance
Area surveys in identifying archaeological features. When choosing which method to apply, archaeologists must judge what techniques will potentially yield the greatest results based on the buried archaeology, the background soil/geology, and what equipment they have at their disposal.

Interpreting the Results

Once we have collected geophysical data, it is then integrated and analysed by archaeologists looking for areas where anomalies or differences in the data exist. Following analysis, archaeologists must interpret the results and make a decision if they believe the feature identified in the geophysics to be a naturally occurring object through geology or geomorphology, or it is an archaeological feature caused by human activity. The resulting decisions are plotted on a map as potentially buried archaeological features which will lead to our greater understanding of the extents and features of a site.

Once potential archaeological features have been discovered through archaeological geophysics, these areas can be exposed through targeted excavation. Like a surgeon would carry out keyhole surgery using an x-ray or MRI scan, archaeologists can insert targeted excavation trenches into sites which allow us to visibly see and understand the archaeological feature which is causing the geophysical anomaly, whilst not having to open up the whole site.

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23 April 2021• Tool kit

Aerial Survey

News Letter

Introduction

Aerial photography remains a powerful way to document and illustrate the landscapes of Wales and Ireland. The aerial perspective provides a landscape view and site context, the building blocks for broad-brush landscape characterisation and understanding the historic landscape. The bird’s eye view is a powerful way of exploring sites and landscapes, and for certain types of sites (e.g. cropmarks) is the only effective way of discovering monuments and placing them on record. Within CHERISH aerial photography provides an immediate record of the condition of eroding coastal sites, and allows entire regional coastlines to be rapidly surveyed from the air following storms. Beyond the archaeological uses for recording during primary reconnaissance, interpretation and mapping, they provide excellent materials for teaching and illustration.

The use of aerial photographs in archaeology has a history extending back more than 100 years and is recognised as one of the most effective ways of recording sites and landscapes. Archives of aerial photographs are a rich source for identifying otherwise unknown monuments and can provide unique records of landscapes and sites that have been changed or destroyed, while new aerial photography provides a means of recording during primary archaeological reconnaissance. There are three approaches to taking aerial photographs; firstly routine survey to photograph a pre-defined area of land (e.g. area-coverage vertical, usually for planning/cartography/military intelligence) and secondly archaeological reconnaissance by an airborne observer who photographs objects seen and understood to be of interest. The third, recent innovation has been the use of drones or Unmanned Aerial Vehicles (UAVs) to carry out local aerial surveys of historic sites and buildings.

Aerial photography

Aerial reconnaissance is widely used around the world and is part of the wider discipline of ‘remote sensing’, surveying archaeology in the landscape without actually touching it, as one would do in an excavation. ‘Aerial archaeology’ encompasses a wide variety of survey and recording activities, from observing the landscape from above and actually taking the pictures to interpreting and mapping sites from the photographs taken. Aerial photography captured from a fixed-wing aircraft remains one of the most powerful tools to document and monitor the coastal heritage of Wales and Ireland. ‘Oblique’ aerial photographs taken at an angle to the ground give a more realistic landscape view of sites and monuments. ‘Vertical’ aerial photographs are taken looking straight down and look more like a map.

Carrying out surveys using a light aircraft means that hundreds of miles of coastline can be covered during periods of just 3-4 hours. The elevated perspective helps to clarify the layout of complex monuments, or show up features on a site which may be hidden from view or difficult to access at ground level.

Times of flights will vary with the seasons. Winter and spring is ideal for the photography of upstanding earthwork monuments, when low vegetation and low light allows all the details of a site to be picked out. Flat light or overcast conditions are preferred for recording monuments for Structure from Motion 3D modelling. Flights in summer droughts can reveal ‘cropmarks’ of buried or lost elements of an archaeological site, often with remarkable clarity

There is plenty to see when flying over the coastal, intertidal and maritime zone. As well as reconnaissance for, and discovery of, timber and stone built fish traps or wrecks and hulks, the search can be successfully extended for some distance offshore through shallow seas on very calm days when coastal waters may be remarkably clear. This is particularly important for recording wrecks which may show well against sandy sea beds.

Photos taken during CHERISH of eroding coastal archaeological sites will stand as a record of the condition of a monument long into the future, allowing comparison with historic aerial photographs taken from the 1940s onwards and charting future change. Powerful software also allows individual aerial photos taken from a drone or light aircraft in orbit around a site to be combined into a highly accurate 3D rotatable model (a process known as Structure from Motion).

Cropmarks

When archaeological features are buried they can affect the growth rate of the crops above them. The presence of features such as buried wall foundations or compacted floor surfaces produce a reduction in the soil depth and lower moisture levels than the surrounding land. Crops immediately above these features tend to have reduced growth rates in comparison to the plants above of no archaeological activity, producing “negative cropmarks”

In contrast areas where ditches, pits and other features have been dug into the subsoil become filled over time. This relative increase in soil depth and the potential to provide increased soil moisture enables the crops above to grow higher and ripen later than the plants around them, producing “positive cropmarks”. Both negative and positive cropmarks are more easily detected from the air and are usually visible during times of drought when crops are at maximum stress.

Soilmarks

Soilmarks Over time human activity has the potential to disturb the local soil profile. As humans dig pits or ditches into the soil or introduce new stone structures they can affect the viable appearance of the soil at the surface. Features such as pits and trenches over time become in-filled with material often different in nature than the surrounding undisturbed soil, including differences in texture (e.g. grain size) or colour. Buried structures such as walls and compacted stones can be brought to the surface by ploughing and are often brighter that the surrounding soil. Soilmarks are usually present after ploughing in the autumn or spring.

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12 April 2021• Tool kit

Airborne Laser Scanning (ALS)

News Letter

Airborne Laser Scanning

Airborne laser scanning (ALS) (also known as LiDAR) is an active remote sensing technique that is used to create accurate and precise 3D models and visualisations of landscapes. As with most innovative technologies, ALS has its origins in the military where it was first developed to carry out underwater scanning to identify submarines. In the UK it was widely adopted during the 90s where it was used initially by the Environment Agency to create terrain maps to assess flood risk. However, it was not until the turn of the millennium that the potential of ALS for archaeological survey began to be recognised.

In practice, a ALS survey consists of the transmission of an active laser beam from a fixed-wing aircraft towards the ground. The reflection of the beams transmitted back to the aircraft are then measured to give distance values which are used to create a 3D Digital Elevation Model (DEM) of the landscape below. The intensity of the returning beam can also give an indication of the type of material that the beam was reflected from. This coupled with the height data can be used to identify and remove vegetation from a DEM, which in turn offers a view of hidden features and landscapes that may be obscured by vegetation. Global Navigation Satellite Systems (GNSS), or Global Positioning Systems (GPS) as it is more commonly known is also used during a survey to ensure that the 3D model is geo-located on the earth.

Using ALS on the CHERISH Project

ALS has been used by CHERISH as a way of investigating and recording the archaeology of some of the more remote areas around our coastlines. Beyond the project it will also be extremely helpful for monitoring of environmental changes such as coastal erosion and sea-level rise.

The first CHERISH ALS surveys were flown in 2017 for six islands in Wales (Puffin Island, Skerries, Bardsey Island, St Tudwal’s, Ramsey Island and Grassholm Island). The 0.25cm resolution data has been used to accurately map archaeological features to produce new maps of all upstanding archaeology on each island. In Ireland, an ALS survey has been commissioned for the area surrounding Dublin bay. ALS data has also been used alongside aerial photography from which several cropmarks have been discovered across the islands.

Publicly accessible LiDAR data

LiDAR data is becoming increasingly available and can often be viewed and downloaded free of charge. National LiDAR datasets can be downloaded from the following sites:

Wales: Lle Geoportal
Ireland: Open Topographic Data Viewer

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24 March 2021• Tool kit

Archival Research

News Letter

Archival Research

Archives of museums, government organisations, libraries and research bodies have historical documents that assist with the analysis of coastal change. They also allow study into the importance of the heritage under threat by revealing finds and important events. Many of these sources are becoming publicly accessible on websites.

Historical Maps

The British Library in London has atlases, maps and charts of harbours drawn for trade and defence. They also have drawings by visitors and officials of the towns and countryside. Many of the historical charts and sailing directions from the Admiralty have moved to the British Library but some remain in Taunton. This includes the hand-drawn surveys by the sailors. Charts often include sailing views of how the coast directly looked to the surveyors.

National Archives Kew has titles to shipwrecks, letters from captains about storms and dangers to shipping from the 17th century, construction of Napoleonic coastal defences, and correspondence about harbour improvements. The National Archives of Ireland has similar harbour development such as the 19th-century dredging of the River Boyne that removed ancient fords but allowed access upriver to Drogheda.

The National Library of Ireland includes piloting directions around the coast. Trinity College Dublin and University College Dublin have map libraries and online resources. The National Museum of Ireland has a topographic archive of correspondence and descriptions about artefact discoveries. The National Monument Service holds many records of archaeological sites, including a shipwreck inventory, with information on surveys and excavations. This includes aerial surveys and older photographs of coastal monuments to compare with the site today.

Antiquarian Illustrations

Museums such as the National Maritime Museums in Dunlaoghaire and Greenwich have further charts, drawings and photographs on display. They also have artefacts for comparison with that found on coastal surveys. This can lead to understanding navigation and use of the coastal sites.

The Royal Irish Academy and Geological Survey Ireland have many images made by early documenters of the coast such as Thomas Westropp and George Du Noyer. Du Noyer was a geologist who painted coastal scenes in the 19th century. Westropp described many promontory forts around the turn of the last century.

There are further more local archives for counties, towns and harbours such as Dublin Civic, Dublin County, and Dublin Port. Then there are private archives, accessed with special permission, such as Woodhouse Estate in Stradbally, Co. Waterford.

Historical Documents

Historical documents can provide precisely dated, detailed descriptions of weather observations. These can be used to extend records of instrumental observations and to calibrate and increase confidence in natural archives of climate variability such as those from tree rings or sediments. Of particular interest for CHERISH are meteorological observations found in harbour, coastguard and lighthouse log books, where readings of pressure, wind direction, rainfall and temperature were noted often several times a day over many years. Many sources are yet to be digitised and transcribed into a usable format for climatological research although a huge effort is ongoing to rescue weather data through citizen science initiatives such as the Old Weather Project and Weather Rescue. We aim to retrieve records from CHERISH project study areas for analysis and to make them available for the scientific community.

Archival sources not only contribute to the construction of detailed time climate and weather histories but also provide a deeper narrative of an individual or community’s experience of extreme weather. Here, we can examine the ways in which people responded to specific events, how prepared they were and the types of coping strategies that were adopted. There is a wealth of material housed in our national repositories at the National Library of Wales and the National Archives of Ireland as well as in numerous regional archives and libraries. Members of the CHERISH team have been involved in the development of a database (TEMPEST) of narrative accounts of historical weather extremes across the UK as part of the AHRC funded project Weather Extremes. We will be building on this and previous research in Ireland (e.g. Sweeney, 2002) by gathering evidence on historical storms, flooding and coastal change and associated impacts from a range of sources such as personal diaries and correspondence; travelogues; newspaper reports; log books; maps; charts and literary sources.

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Climate Change & Coastal Heritage

Tool kit

Palaeoenvironmental Research

News Letter

Introduction

Palaeoenvironmental Sampling

Optically Stimulated Luminescence (OSL) Dating

Related Content

Other Activities

Geophysical Survey

News Letter

Introduction

Electrical Resistance

Magnetic gradiometry

Ground Penetrating Radar (GPR)

Interpreting the Results

Related Content

Other Activities

Aerial Survey

News Letter

Introduction

Aerial photography

Cropmarks

Soilmarks

Related Content

Other Activities

Airborne Laser Scanning (ALS)

News Letter

Airborne Laser Scanning

Using ALS on the CHERISH Project

Publicly accessible LiDAR data

Related Content

Other Activities

Archival Research

News Letter

Archival Research

Historical Maps

Antiquarian Illustrations

Historical Documents

Related Content

Other Activities

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