Environment Agency Lidar data shows archaeological potential

The announcement earlier this year that the Environment Agency was to make its Lidar data freely available was welcomed by archaeologists, who are able to use the detailed terrain height data to add a new dimension to existing aerial photographs, and provide a new source of data for studying archaeological features.  This is of particular importance to amateur archaeologists, who are unable to afford the cost of commercially acquired Lidar data.  The access to this data, in addition to the maturity of open source computer applications, means that such archaeologists can begin to make a real and effective contribution to the study of landscape features.

Whitsbury Iron Age Hillfort - 1m DTM Lidar

Whitsbury Iron Age Hillfort – 1m DTM Lidar

Lidar data can now be downloaded from the Environment data.gov.uk portal.  Simply click on the map;  a square will appear on the map and the available downloads will appear in a list below.  There are two types of Lidar data:

  • Digital Terrain Model (DTM) – the bare earth, with buildings and vegetation removed
  • Digital Surface Model (DSM) – the model includes buildings and vegetation

For archaeological purposes, the DTM is probably most useful, as trees and bushes are stripped away to reveal any earthworks below.  The downloaded zip includes a series text files with a .asc extension;  these are text files which contain an array of height values for a specific small tile.  Many Geographical Information System (GIS) software packages can read this data directly;  I used the open source and freely available QGIS package.

The most effective way of visualising Lidar data is with some sort of hillshade applied, which simulates the lighting of the landscape with sunlight from a particular direction and height.  The problem with shading from just one direction is that linear features aligned with the direction of shading will not create a shadow.  For archaeological applications, it is normal to create a composite of hillshades from a number of directions, using different colours to represent each hillshade.  I used the excellent and freely available Relief Visualization Toolbox to create these hillshade composites.  The picture above of Whitsbury Hillfort, near Fordingbridge in Hampshire, is an example of this type of rendering.  A vertical exaggeration can be used to strengthen the depiction of subtle features.

Once all of the hillshade images were created, I used a command line tool called GDAL to create a mosaic of all the images, called a VRT file.  GDAL tools are available from the menus within QGIS.  A screenshot is shown below [click on the image to enlarge].

Lidar composite in QGIS

Lidar composite in QGIS

It is worth noting that there is not a full national coverage of EA Lidar data;  most river valleys and surrounding areas are available.  The black areas in the screenshot above are locations where no data is available.

So what have I seen so far during an initial browse of the data in the general region of the Avon Valley?  I have picked out a few areas below.

Whitsbury Hillfort

The screenshot of Whitsbury hillfort above shows the potential for depicting existing earthworks which are normally shrouded in thick vegetation.  The detail shown in the ramparts can be compared to the original Royal Commission earthwork plan, and reveals subtle details not previously recognised.

Bokerley Dyke and the end of the Great Dorset Cursus

Lidar showing the end of the Great Dorset Cursus

Lidar showing the end of the Great Dorset Cursus

[Click on the image to enlarge].  This is perhaps my favourite area, showing a palimpsest of landscape features of true temporal depth.  The end of the Neolithic Cursus can be seen in the centre of the image as a large subtle rectangular feature, which heads off towards the south west corner of the image.  The much clearer long thin linear feature which points at the end of the cursus is a long barrow, as is the similar long barrow to the south.  The former long barrow has long been suspected of being two adjoined long barrows, and this is borne out by the Lidar, which shows two sections on slightly different alignments.  There is another ploughed out long barrow to the north of the cursus, which shows as an oval mound.

The large bank and ditch which snakes from north west to south east is Bokerley Dyke, a linear boundary which probably had significance in the Bronze Age and Iron Age, and was most likely strengthened in the late Roman period.  To the east of Bokerley Dyke, a series of probable Prehistoric field boundaries can be seen.  Finally, the substantial rectangular earthwork in the top centre of the image brings us into the 20th Century, representing an army training range.

Rockbourne Down

Field systems around Rockbourne Down

Field systems around Rockbourne Down

[Click on the image to enlarge].  This image shows an extensive field system on and around Rockbourne Down.  Most of the field boundaries are under plough, but the crisp boundaries to the east of the image are still under pasture and much better preserved.  There also happen to be three long barrows on this image.  The one at the centre top is the huge and well preserved ‘Round Clump’, with the mound and ditches clearly depicted in the Lidar data.  At the western side of the image is the ploughed out Rockbourne Down long barrow, pointing in a SSE direction.  To the east of the image, crossed by the horizontal blue grid line is a much smaller long barrow mound.

In summary, now that the Environment Agency Lidar data is now freely available, amateur archaeologists have at their disposal a rich new source of data to study past landscapes and discover new sites.  The images above show the potential for this resource, which can be used to illuminate even the most subtle earthworks with an unprecedented clarity.

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AVAS members enjoy lecture

At the AVAS lecture for October, AVAS members were treated to a fascinating talk from Dave Fawcett, and expert in historic arms and armour.  In the first part of the talk, Dave talked about the intricate jostling for power among members of the French and English royal families, and how this translated into a series of battles in the Hundred Years War, culminating in the famous Battle of Agincourt.  The second part of the talk concentrated on the arms and armour, and Dave had kindly brought along a number of replica examples which we we able to try out for real.  I have added a number of photos below, and should add that no AVAS members were harmed during playtime with the weapons.  More photos are available on the AVAS Flickr photostream.

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AVAS Lecture Series for 2015-16

The initial programme of talks in the AVAS 2015-16 lecture series has been announced on the meetings page on the main AVAS website.  Some talks later in the year are still to be confirmed, but the first few lectures look really interesting, spanning the Palaeolithic to the Hundred Years War.

Jane Ellis-Schön, Project Director of the Finding Pitt Rivers Project, will open the lecture series on 2nd September 2015.  She will  talk about cataloguing and researching the Pitt Rivers Wessex collection at Salisbury Museum.  The timing of this talk is particularly apposite given the start of the Foundations of Archaeology project, which celebrates the work of the pioneering archaeologists who first identified the rich upland archaeology of south Wiltshire and north east Dorset.  The latter project will be looking at two site excavated by Pitt Rivers:  Wor Barrow and Winklebury Hill.

Visitors are made very welcome at the AVAS lecture meetings, which are held in Ringwood on the first Wednesday of the month between September and May – see the meetings page on the main AVAS website for more details.

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Environment Agency LIDAR data to be freely available

I have just noticed the following announcement on the Environment Agency website:

From September 2015 all our LIDAR data will become Open Data and everyone will be able to use it for free.

LIDAR for Avebury

LIDAR for Avebury

This is on https://environmentagency.blog.gov.uk/2015/06/16/free-mapping-data-will-elevate-flood-risk-knowledge/.  The page states that 72% of England now has LIDAR coverage,and the chances are that the Avon Valley and surrounding areas will be available.  This will be a fantastic resource for investigating the archaeology of our region.

Recently the New Forest made available images of hill shaded LIDAR data, accessed via an index map.  Although this is a very valuable set of data, it is difficult to integrate with other layers of data in a Geographical Information System (GIS), as it is not georeferenced.  The Environment Agency data will be georeferenced, and has the advantage of being raw data, allowing greater control over how the data is displayed, including the ability to exaggerate the data to make subtle features stand out more clearly.

I will post an update in September when I have downloaded some data.

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AVAS at Salisbury Museum Festival of Archaeology – Part 2

Following on from the previous post, AVAS had a second successful day last Sunday at the Festival of Archaeology at Salisbury Museum.

AVAS at Salisbury Museum Festival of Archaeology 2015There was once again a steady stream of visitors, with a number of people expressing an interest in joining AVAS. There were also some familiar faces dropping in to see us:

AVAS at Salisbury Museum Festival of Archaeology 2015

Jan drops in to see us

Mark and Rachel challenged Continue reading

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AVAS at Salisbury Museum Festival of Archaeology 2015

AVAS had a stand at the Salisbury Museum Festival of Archaeology today.  A few of us were up bright and early this morning to set up.  We had a few difficulties erecting the double gazebo after failing to locate the instructions.

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Mark ponders while Vanessa points

However, we were soon setting out a quality display of finds and photos. 20150718_102343
20150718_101534 20150718_101557Our stand was sandwiched between a bunch of friendly Angle Saxons, and the crowd pulling Phil Harding of Time Team fame.

The event was really successful, and we had a steady stream of interested visitors to the stand.  We will be attending once again tomorrow.  There are a few more photos on the AVAS Flickr photostream.

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AVAS Barbeque July 2015

We had great weather on Saturday for the annual AVAS BBQ, once again hosted by Mark on the banks of the River Avon.

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The food was fantastic (thanks to Vanessa, Rachel and family for preparing an array of tasty treats).

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Thanks also to Mark for sorting out the barbeque and allowing us to use his farm as the venue. I have posted some more photos on the AVAS Flickr photostream.

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AVAS now on Facebook and Twitter

AVAS has finally succumbed to the power of social media, and now has a page on Facebook and an account on Twitter.

facebook

If you are a user of Facebook, simply go to http://www.facebook.com/avonvalleyarchsoc and ‘Like’ the page to receive Facebook updates.  AVAS members should let me (Mike) know if you wish to make posts on the page.

twitter

For any AVAS members on Twitter (hopefully more than just me!), the Twitter account is @AvonValleyArch and can be viewed in a web browser at:  http://twitter.com/AvonValleyArch

Our WordPress blog is now linked to both accounts, and posts to the blog should also appear on Facebook and Twitter (I hope!).

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Blog Stats: 2014 in review

The WordPress.com stats helper monkeys prepared a 2014 annual report for this blog.

Here’s an excerpt:

A San Francisco cable car holds 60 people. This blog was viewed about 1,700 times in 2014. If it were a cable car, it would take about 28 trips to carry that many people.

Click here to see the complete report.

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2014/15 Winter Meetings

The remaining meetings for the 2014 / 15 Winter meeting programme have just been added to the main AVAS website.  There is an interesting range of subjects, ranging from the Cerne Abbas Giant, through to Agincourt and the First World War.  To see the programme, please visit the meetings page on the main AVAS website.

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