Climate Change & Coastal Heritage

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7 July 2020• Blog Posts

Using UAV Mapping To Measure Coastal Erosion

News Letter

What is UAV mapping?

The ability to generate mapping from overlapping aerial photographs through a process known as photogrammetry has been a core technique in mapping for many years. Recent developments in photographic processing using a technique known as Structure from Motion (SfM) allows photogrammetric techniques to be used on basic workstations and laptops using low cost software. SfM analyses overlapping images and uses pixel matching techniques to extract the geometry of the subject of the photography. When this is combined with the ability to capture aerial photographs from an Unmanned Aerial Vehicle (UAV) or drone it creates a powerful and flexible mapping system.

The product of the Structure from Motion processing is a Digital Surface Model (DSM) of the local area with a remarkably high resolution. The survey resolution is generally in the range of 2 – 5cm, even working with photography from an entry-level UAV.

Phantom 4 Pro UAV flying a mapping survey at Glascarrig Motte, Co Wexford.
Phantom 4 Pro UAV flying a mapping survey at Glascarrig Motte, Co Wexford.

A critical element of this process, particularly if change detection is the primary objective, is the ability to accurately place the DSM in its true geographical position. This is most probably a national mapping system such as Irish Transverse Mercator (ITM) in Ireland. Global Navigation Satellite Systems (GNSS) are needed, either through built-in sensors on the UAV or through the use of accurately surveyed ground markers. When this is done a baseline survey has been established against which a future survey, carried out to the same specification, can be compared. Change can then be identified and quantified.

GNSS survey control being measured on a ground control target
GNSS survey control being measured on a ground control target

Glascarrig Motte & Bailey, County Wexford

The site of Glascarrig motte and bailey is located on a slight promontory overlooking the coast. In 1167, Diarmuid Mac Murchada landed at Glascarrig on his return to Ireland, having requested the help of King Henry II to recover his kingdom of Leinster. The motte and bailey castle were probably constructed by William de Caunteton at the end of the 12th century. In 1311, Glascarrig was destroyed by MacMurchadas. At this time a substantial settlement consisting of 48 burgages is recorded at Glascarrig and the site may have been abandoned after this attack.

The motte, a grass-covered flat topped mound, almost 6m in height and 36m in diameter, is defined by a flat bottomed fosse. To the south of the motte is an enclosed area or bailey which is outlined by an earthen bank. The site is located in an area of glacial drift making it particularly susceptible to erosion. Erosion of the eastern extent of the bailey and the fosse has produced a rich collection of pottery and animal bones.

UAV Survey at Glascarrig Motte

DJI Ground Station Pro app was used to programme the survey parameters in advance of a mapping survey
DJI Ground Station Pro app was used to programme the survey parameters in advance of a mapping survey

The motte and its landscape setting have been mapped by UAV survey twice so far for the CHERISH project (June 2018 and February 2019). The 2018 survey established the baseline, against which future surveys could be precisely compared to detect change.

The surveys to date have used the same UAV, and produced over 400 images, ready to be processed through SfM software. To ensure the survey could be precisely mapped to ITM, GNSS control was achieved. A DSM and orthoimage of the motte were produced, with a resolution of 2.5cm, and positional accuracy, in ITM, to a survey-grade of better than 2cm.

Agisoft Photoscan processing stages; the photography aligned ready for Digital Elevation Model (DEM) extraction, and the resultant DEM
Agisoft Photoscan processing stages; the photography aligned ready for Digital Elevation Model (DEM) extraction, and the resultant DEM

Glascarrig GIS analysis

To assess whether any change has taken place the two DSMs are interrogated in our Geographical Information System (GIS). A shaded relief model of each DSM allows a visual comparison to be made, which suggests no dramatic change has taken place.

A visual inspection is highly subjective, it is not particularly scientific and could potentially miss small but significant changes in the landscape. GIS allows us to do much better than this through mathematical calculations to compute the differences and graphically display them on a deviation map.

isual comparison between the shaded relief models created from DEM data captured in June 2018 (left image ) and February 2019 (right)
isual comparison between the shaded relief models created from DEM data captured in June 2018 (left image ) and February 2019 (right)

What does this tell us?

The deviation map confirms that very little has changed at Glascarrig over the time period June 2018 – February 2019; the site has remained stable. This is perhaps not a great surprise as this is a relatively short time period, and without a major storm event. The majority of the site is within the +/-0.1m range but there are some areas, the blue tones, which were higher in 2018. This can be explained by differences in seasonal vegetation growth, a June survey in 2018, and a February survey in 2019. This is a lesson learned that when planning repeat surveys where possible the time of year should be matched. The red tones at the eastern edge of the area is a pebble beach, which appears to be higher in 2019, indicating the dynamic nature of the foreshore.

This analysis, although not revealing any significant damage at the site on this occasion, has been incredibly informative in testing the value of the technique. It gives confidence that repeat UAV mapping will reveal the extent of any erosion at our monitoring sites should any occur in the future.

Deviation map showing the height difference calculated in the DEM's from 2019 and 2018
Deviation map showing the height difference calculated in the DEM's from 2019 and 2018

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5 June 2020• Blog Posts

Mining and Erosion along the Copper Coast

News Letter

Waterford’s Copper Coast, with its proliferation of promontory forts and reports of severe erosion, is a case study area for the CHERISH project. The area is known as the Copper Coast after the mineral deposits there that were mined extensively from 1824 to 1908.

At least 26 promontory forts survive on cliffs of up to 70m high and research at Irish promontory forts including Drumanagh and Dalkey Island in Co. Dublin and Dunbeg in Co. Kerry suggest their use from the Iron Age to early medieval periods. Ogham stones recorded along the Co. Waterford coast at Knockmahon, Island and Kilgrovan suggest that there were ecclesiastical sites in the surrounding area in the 5th- to 7th-century.

The National Museum of Ireland’s (NMI) topographic files record the finding of a number of objects in the area which indicate a long history of mining. The Reverend Patrick Power (1909) described a circular copper ingot of Romano-British Type found around 6km upstream from the estuary at Bunmahon. A group of finds given to the NMI in 1850 included two paddle-shaped instruments of oak found a depth of 20m. They were ‘apparently of great age’ in the 19th century. The description of their long narrow handles and spoon-shaped blades indicate that they could have been used to gather up broken fire-cracked rock, a product of the mining process. An Irish 17th-century trade token found near Knockmahon Castle could have been lost by merchants or seafarers transporting the natural resources produced by mining activity.

While undertaking aerial surveys and geophysical surveys on the promontory forts on the Copper Coast, the CHERISH team has inevitably come across the evidence of the mining: adits or entrances to underground mines in the cliffs, mine shafts and spoil heaps above the cliffs, along with ore yards and engine houses.

The mineral resources of the Copper Coast may have been important since prehistoric times, although much of that evidence has probably been disturbed by post-medieval mining and erosion. Sixteenth century historical sources record mining near Knockmahon promontory fort and in the mid-18th century, Francis Wyse from Waterford City, took a lease for the mineral rights west of Bunmahon (Cowman, 1983). Above the beach west of Bunmahon Head promontory fort, in Templeyvrick townland, the entrance to underground mines can be seen. Many mines along the coast were worked for up to 400m out to sea.

 

Templeyvrick mines on Trawnamoe Strand beside Bunmahon Head.
Templeyvrick mines on Trawnamoe Strand beside Bunmahon Head.

Beside the Knockmahon promontory fort is a landing place called Stage Cove. It has a modern concrete slipway today but at low tide it is possible to see that the access through the bedrock has been cleared. This would have allowed larger vessels to land and access the ore yard. In 1863, copper ore was being shipped from here to market in Liverpool and Swansea, when weather permitted boats to come close to the shore (Du Noyer, 1865). A UKHO chart dating from 1849 depicts vessels anchored off the ore yard in a sailing view.

 

Stage Cove landing place at low tide, Knockmahon
Stage Cove landing place at low tide, Knockmahon
UKHO sailing view from 1849 showing ore yard and engine houses around Knockmahon (L7194).
UKHO sailing view from 1849 showing ore yard and engine houses around Knockmahon (L7194).

Thirteen adits have been recorded into the cliff at Illaunobrick promontory fort or Danes Island in the townland of Ballynarrid. It has been suggested that the mines in the area could have been worked in the Bronze Age. This has been refuted by Historian Des Cowman (1982) using local records and through the identification of a drill hole which suggests that most of the evidence we see today are the result of are Industrial period mines. Mostly inaccessible today, these mines have contributed to the cliff erosion and there is very little trace of the promontory fort embankment defences today with only an impassable ‘goat track’ onto the stack. The 1840 edition of the Ordnance Survey map marks ‘site of entrenchment’ on the landward side of Illaunobrick and Thomas Westropp (1914-16) says it was nearly gone by 1841. Local knowledge records cliff rock falls around Ballynarrid and the neighbouring townland of Ballydowane in the 1970s and 80s.

 

Illaunobrick with mines into the cliff
Illaunobrick with mines into the cliff

This abundant heritage of the Copper Coast indicates this was an area with rich mineral, marine and agricultural resources, attracting settlement that traded across the Irish and Celtic Seas perhaps as far back as the Iron Age. The surveys conducted to date allow us to create a baseline record of the site against which future erosion can be measured. It also allows us to cast further light on the varied history of the region from prehistory to the more recent past.

References

  • Cowman, D. (1982) Bronze-Age Copper-Mines at Dane’s Island. Decies 20: 22-7.
    Cowman, D. (1983) Thomas (“Bullocks”) Wyse: A Catholic Industrialist during the Penal Laws, I. Decies 24: 8-13.
  • Du Noyer, G. (1865) Explanation to Accompany Sheets 167, 168, 178, and 179 of the Maps and Sheet 13 of the Longitundinal Sections of the Geological Survey of Ireland illustrating Parts of the Counties of Waterford, Wexford, Kilkenny and Tipperary. Hodges, Smoth and Co., Dublin.
  • Power, P. (1909) ‘On an ancient (prehistoric?) copper ingot from Bonmahon’, J Waterford SE Ir Archaeol Soc 12, 86-89.
  • Westropp, T 1906, ‘Notes on certain promontory forts in the counties of Waterford and Wexford’, J Roy Soc Antiq Ir 36, 239-58.
  • Westropp, T. 1914-16, ‘Fortified headlands and castles on the south coast of Munster: Part II, from Ardmore to Dunmore, Co. Waterford’, Proc Roy Ir Acad C 32, 188-227.
  • Westropp, T. (1920) The Promontory Forts and Traditions of the Beare and Bantry, Co. Cork Royal Society of Antiquaries of Ireland 10 (2): 140-159.

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The CHERISH Techniques graphic showing the multidisciplinary nature of our work

27 May 2020• Blog Posts

Should we call ourselves digital archaeologists now?

News Letter

From Indiana Jones to Time Team, most people are familiar with the role of an archaeologist. We are often perceived as people that dig holes in order to find old things to stock museums, although I am sure there are one or two archaeologists out there that do run around tombs! While excavation does form a core part of the discipline there are many of us who rarely set foot anywhere near an excavation trench such as the aerial photographers, scientists, surveyors and finds experts. The multidisciplinary nature of archaeology epitomises the challenges we face when attempting to uncover and reconstruct the lives of past humans, a complex task that involves more than digging up pottery and gold. As with many sciences, archaeology is constantly evolving, embracing new technologies and techniques to not only improve our understanding of the past, but to bring it to life in present and preserve it for future generations. Moving with new technologies is also key to successfully managing our cultural heritage in the face of innumerable threats.

As a project looking at the threats of climate change on coastal heritage it was important that we adopted modern techniques in order to record, monitor and further our understanding of some of our most endangered sites around the coast. This is being achieved by using a whole host of different techniques, beautifully illustrated in our new ‘techniques’ graphic!

Much of this work involves the use of digital technologies such as drones, satellites and GPS, terrestrial laser scanning and aerial laser scanning to record archaeological sites as they currently appear. Using this technology, we can gather data and information for archaeological sites faster and in more detail than ever before. Recording in digital not only speeds up our work but makes it easier to carry out more complex analysis, reconstruct sites and publicise the results through forums such as social media. Working in this way is especially important during these strange times where the only way to access and explore archaeology for both us as archaeologists and the public is through our computer screens. But how is this possible, how can we ‘do’ archaeology from the comfort of our own homes using digital data and what has CHERISH been up to digitally since the project began? Being stuck inside has allowed some of us CHERISH folk to reflect on a few of the digital things that we have been up to over the last few years.

The different LiDAR visualisations that can be produced
The different LiDAR visualisations that can be produced

When I first arrived as a young archaeologist on CHERISH I was given the task of processing the LiDAR (lasers scanning carried out from a plane) data for six Welsh islands – a pretty daunting task for someone who had barely worked with 3D data before! This work involved the use of software to process the laser point data to get it prepared for interrogation for archaeological features. Different visualisations were produced to show 3D representations of the islands’ topography and archaeology using a clever piece of software known as the Real Visualisation Toolbox created by the Research Centre of the Slovenian Academy of Sciences and Arts. The different visualisations enabled us to see the islands as never before…  

A few months working with the data and I was hooked. Searching for archaeology on the islands (which at this point I had never visited) became a new pastime. Countless archaeological features (some previously unknown) were mapped and recorded to produce new maps of all upstanding archaeology on each island, something that had not been done to such detail before. Bardsey Island (located at the tip of the Llyn Penisula) was by far the most impressive island mapped. An island coated in medieval and post-medieval field systems was revealed on the LiDAR, providing an insight into the farming past of the island. We were also able to take this further by looking and historical estate maps created for the Newborough estate in the 18th and 19th centuries for clues as to how the island was divided and farmed in the past. When overlaying the digitised maps on top of the LiDAR it became clear that some of the ploughed ridge and furrow visible on the LiDAR was in fact related to field systems visible on the historic mapping. However, many still didn’t respect these field boundaries, enabling us to push their dates further back into the post-medieval period. The remarkable thing was that most of this work had been carried out from an office miles away from Bardsey – a true piece of digital archaeology.

Map showing all visible archaeological features on Bardsey Island including all of the ridge and furrow shown in teal.
Map showing all visible archaeological features on Bardsey Island including all of the ridge and furrow shown in teal.

The use of drones also forms a huge part of our digital survey work which is being carried out extensively in both Wales and Ireland. This is also an area of archaeology that, before arriving on CHERISH, I had very little idea about, but over the last few years it has in a way become my bread and butter. Drones (or UAVs) are steadily becoming a standardised tool used in the recording of archaeology and this is certainly the case on CHERISH where they have been deployed at almost all our sites. In our case, many of our sites are too dangerous to survey by any means other than using drones. High and crumbly cliffs are dangerous and best avoided by us archaeologists! However, these circumstances are where drones come into their own with their ability to record sites and eroding cliffs quickly and safely.

Clearly, visiting the sites is required to collect the initial data which is done by taking 100s of overlapping aerial photographs, however, most of the work is actually done from the comfort of the office (or bedroom now!). The main aim at the post-processing stage is to take all the photographs of an individual site and ‘stitch’ them together to create 3D data that can then be turned into numerous different outputs. This is achieved using software such as Agisoft Metashape which uses a technique known as photogrammetry to build 3D point cloud data by matching common points between the overlapping 2D photographs. From this process we are left with thousands or sometimes millions of points that represent the true shape and size of the monument (think what the site would look like if millions of small bouncy balls were placed all over the monument).

A 3D point cloud of Dinas Dinlle, Gwynedd
A 3D point cloud of Dinas Dinlle, Gwynedd

We can use this point data to compare against previously collected data to carry out monitoring work. This is done in software such as CloudCompare which takes two point clouds, matches them up and then runs analysis to identify parts of a site that have metrically changed. Quantifying loss and identifying the weaker areas of sites is an important part of CHERISH’s work which will help in the management of sites against the complex risks climate change poses. This work has been done to good effect in Ireland where sites such as Dunbeg, County Kerry have suffered huge amounts of loss due to coastal erosion caused by increasing storminess in the region.

Huge loss at Dunbeg promontory fort, County Kerry
Huge loss at Dunbeg promontory fort, County Kerry

Another key aim of the project is to raise awareness of the archaeology of sites and the climate change risks they face. Drones (unsurprisingly!) also feature heavily in this aspect of our work where we use the drone data to produce digital 3D models to share online and use as outreach tools. We create these models by ‘meshing’ the points into a solid digital object which can then be shared online. As this is beyond my skill set we usually send off the data to expert 3D modellers (such as our friends at ThinkSee3D) to take our data and turn them into beautiful models that we can then upload to SketchFab for the public to have a look at and explore. During this period, we have taken the opportunity to produce ‘digital tours’ using annotations on SketchFab that highlight the visible (and sometimes hidden) archaeology as well as the types of climate change risks that they face. Have a look yourselves!

3D printing is also becoming a popular way of bringing digital data back into the real world to use as effective outreach tools. Before the lockdown we were keen to get a few of our sites printed to help us in our public engagement work. Thankfully, we were able to get a lovely print of Dinas Dinlle in Gwynedd which has been used instrumentally in describing the site and highlighting how it is being affected by coastal erosion. It has also proved to be a hit with school children across Wales! In the future we hope to take this work forward and to begin to develop site reconstructions and digital animations showing how sites previously appeared and how climate change is dramatically changing their appearance today, so watch this space…

Engaging with schools using drones and 3D models
Engaging with schools using drones and 3D models

So, coming back to the question ‘Should we call ourselves digital archaeologists now?’ I’m still unsure, but what is clear is that the digital ways of ‘doing’ archaeology are steadily becoming mainstream practices, especially in the archaeological survey world. We can never substitute fieldwork purely with remote and digital methods (and it must be said that I am greatly missing the fieldwork!) but who knows, perhaps the current lockdown situation will force us to adapt our methods and drive the digitisation of all of those beautiful maps and interesting historical documents that are tucked away in the dark corners of archives across the country. Digital archaeologists? Perhaps not. But archaeology could become a whole lot more accessible to people as efforts are stepped up by archaeologists to continue to engage with people during this difficult time.

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12 May 2020• Blog Posts

An Introduction to Ireland’s Eye

News Letter

Ireland’s Eye, located in the Irish Sea, north of Dublin City is the landmark that tells air travellers from the East that they are about to land in Dublin. The island has a fascinating story to tell and its long history is reflected in the built heritage that survives on the island; prehistoric promontory forts, Roman finds, a church with a long history and a Napoleonic era defence tower. The written histories of the island include accounts of monastic settlements and Viking raids.

The CHERISH team had made a number of visits to Ireland’s Eye with the aim of adding to the current archaeological record for the island and developing an understanding on how this Island is being effected by climate change. Ireland’s Eye differed from other CHERISH case study sites as accretion (the deposition of additional materials) along the western coastline was the main coastal process in action.

The Dinnseanchas, originally composed in the sixth century, tells us that the Island was known as Inis-Ereann the island of Eria. Afterwards the island name changes to Inis-mac-Nessan, from the three sons of Nessan, a prince of the Royal family of Leinster. The present name Ireland’s Eye comes from an Anglicisation of the Viking name for Inis-Ereann where ey denotes ‘island’. Some of the earliest evidence of activity on the Island are the Promontory forts, these sites are typically associated with the Iron Age, though some had long histories of use. Prior to this survey, only one promontory fort was recorded on the Island. The team will update the sites and monuments record with the newly identified promontory forts. Two coins from the Roman Empire found on the Island provide evidence of the Iron Age Ireland’s interaction with Roman Europe, and are possibly contemporary with the first use of the promontory forts.

Staff surveying the promontory fort on Ireland's Eye
Staff surveying the promontory fort on Ireland's Eye

The church is referred to as Kilmacnessan or St Nessan’s Church and the three sons of Nessan reputedly founded a monastery here in the 6thCentury AD.  While the historical accounts indicate there was a church on the island in the 6th century, the current structure appears to date to several centuries later. A 12thcentury date is suggested for the church due to its nave and chancel construction with a single entrance in the west wall. This is supported by the parallels with the Church of St Michael of Pole in Dublin City and documentary evidence which records that the church was transferred to the mainland, in 1235 AD. The church was heavily restored in the 19thCentury. Ploughing exposed stone coffins in close proximity to the church in 1868, indicating an associated cemetery.

Heritage week event at the Church on Ireland's Eye
Heritage week event at the Church on Ireland's Eye

The Annals of the Four Masters says the island was besieged by Foreigners from Dublin in 897 AD and plundered in 960 AD (Gwynn & Hadcock, 1988). The Annals of the Four Masters detail how the in the late ninth century the Vikings made an encampment which was besieged by Irish forces and in 960 AD a Viking fleet plundered the monastery. Another highly visible structure that dominates the north-west of the island is a Martello tower. It was established on the Island in 1805/1806 AD as part of the Napoleonic era coastal defence system along the Irish coastline.

Heritage week event at the Napoleonic Era Tower on Ireland's Eye
Heritage week event at the Napoleonic Era Tower on Ireland's Eye

In Summer 2019 we co-hosted a very successful heritage walk and beach clean with Clean Coasts. The accretion occurring on the west side of the island means that waste materials are being deposited along with beach sediments. The CHERISH team explained both the history and built heritage of the island as well as the geological heritage. And while the team explained our research to the participants, we also learnt lots from the very knowledgeable and informed locals, including members of the local history and archaeology group Resurrecting Monuments. We are looking forward to returning to Ireland’s Eye to carry out further research including geophysical surveys.

Read more about the archaeological sites on the island on the National Monuments Service Historic Environment Viewer

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Puffin Island from the air, June 2019

7 May 2020• Blog Posts

A new survey of Puffin Island

News Letter

Puffin Island or Ynys Seiriol/Priestholm rises in a steep ridge of limestone off the eastern coast of Anglesey in north Wales. This magical, privately owned island is home to protected seabirds, principally cormorants, and the ruins of an early medieval monastery. No public landing is allowed without the prior permission of the landowner.

The monastery of Priestholm, an early medieval foundation of which the listed and scheduled tower of the Augustinian priory church still stands proud on the island’s skyline, has long attracted visitors. In 1868 Herford Hopps carried out a basic survey of the buildings and discovered numerous skeletons around the church where rabbits had disturbed the bones. Harold Hughes returned in the final years of the nineteenth century to carry out more accurate surveys of the buildings and to continue with his own excavations, finding remains of an early shrine pre-dating the church tower. The Royal Commission first visited in 1929 to survey the island for their 1937 Anglesey Inventory. The only other substantial building on the island is the listed, ruined 19th century Telegraph station at the north-east point.

In modern times the island and ruins had become overgrown and lacked a modern survey. Therefore Puffin Island was selected as a new study site for the EU-funded CHERISH Project due to its general inaccessibility, the protected status of the buildings and to enable new, highly detailed surveys of the structures to be made to monitor future change and erosion. The CHERISH ‘toolkit’ approach meant that the island would be completely surveyed from the air, on the ground and from the sea.

In 2017 CHERISH commissioned new airborne laser scanning (‘LiDAR) of the entire island. The highly accurate laser penetrates the woodland canopy allowing trees and scrub vegetation to be digitally ‘stripped away’ in a computer. Using this technique we were able to map previously hidden fields, buildings and a new promontory enclosure to build a virtual view of the entire island.

Spectacular 3D LiDAR views of Puffin Island with and without its woodland vegetation
Spectacular 3D LiDAR views of Puffin Island with and without its woodland vegetation

Remote sensing can only tell part of the story. In June 2018 CHERISH and Cadw staff accompanied seabird specialist Dr Jonathan Green out to Puffin Island in something resembling a ‘Famous 5’ adventure, beginning with a boat landing among basking seals on the western beach. Negotiating chest-deep grass and brambles and crawling under branches of low trees whilst carrying heavy survey equipment, we reached the peace and solitude of the 800 year old church. The limestone Romanesque tower looked quite continental in the June sun. Seagull chicks looked on as we laser scanned the tower.

Later that summer the Geological Survey of Ireland carried out marine bathymetry along the east Anglesey coast, monitoring wrecks and mapping the inshore island waters. We returned in decidedly colder weather in November 2018 to fly a drone over the tower to gather 3D photos of the parts the laser scanner couldn’t reach.

The new surveys generated state-of-the-art 3D records of the medieval priory church and associated structures, allowing any future change to be measured to within a few millimetres. The marine survey data has been linked to the LiDAR to produce a remarkable seamless onshore/offshore 3D map of the entire island. The current lockdown and a break from active fieldwork has provided the opportunity to write up the various surveys into a substantial archive report, which will be made available during 2020.

3D drone photogrammetry of the church tower
3D drone photogrammetry of the church tower

The CHERISH Team hope to return to Puffin Island in 2021 to make a final monitoring visit of the medieval ruins, and to savour the peace and isolation on this wilderness island one last time.

See our online records for Puffin Island here:

Find out more here

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