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LIDAR - looking beneath
#1
From a news release : NEWS RELEASE No: 8932 Forestry Commission

Interesting stuff this... thought you might like to be kept up to date (ish)

http://www.forestry.gov.uk/newsrele.nsf/...enDocument

Laser beams shone down from the sky are revealing archaeological and other treasures hidden in Britain's forests - by "seeing through" the trees.

Scientists, archaeologists and foresters are using pulses of laser energy beamed down from aircraft flying about 1000 metres (3300 feet) up to reveal forests' hidden secrets. These can include sites of ancient settlements, fortifications, farms and other signs of human activity which, in woodland, are often difficult to detect from the ground or the air with the naked eye.

Called lidar ('light detection and ranging'), the technology works by "bouncing" harmless laser energy off the forest in much the same way as radar ('radio detection and ranging') bounces radio waves off solid objects, and measuring the time it takes for the pulses to be reflected back to the recording instruments in the aircraft.

This produces data in the form of millions of three-dimensional co-ordinates. Many of these co-ordinates represent the pulses that "bounce" back off the trees themselves, but special computer applications can strip these out, leaving only the co-ordinates of the pulses that made it through the gaps in the vegetation to the forest floor. These data can then be fed into mapping computers that can convert them into images of the ground that look as if the trees had been stripped away.

By this means, any ground features that look as if they might have been made by humans rather than nature can easily be spotted and investigated to see whether they indicate the presence, or former presence, of buildings, trenches, fortifications, fields, charcoal platforms, mining sites or other features.

Lidar works best on deciduous forests in winter, when the leaves have fallen off the trees, giving the greatest number of laser pulses the best chance of reaching the ground rather than being reflected off leaves and needles. It works less well in evergreen conifer woodland such as spruce and pine forests, where the presence of needles on the trees all year round prevents of a lot of the laser energy from reaching the ground. Nevertheless, it can still reveal some archaeological features in well thinned conifer woods.

One of the first uses of lidar to find archaeological features in British forests was a survey of 280 square kilometres (108 square miles) of Gloucestershire, including most of the Forest of Dean. Carried out by scientists and archaeologists from the Forestry Commission and its Forest Research agency, Gloucestershire County Council, Cambridge University and English Heritage, it was the largest single heritage survey of woodland ever undertaken in Britain.

After eliminating known features, this survey revealed hundreds of features or areas of features that Jon Hoyle of Gloucestershire County Council Archaeology Service believes are worthy of further investigation and which have caused considerable excitement among archaeologists. These include industrial remains, parkland features, and what might be banks and terraces, enclosures, areas of coal extraction and areas of charcoal pits or platforms - a relic of the area's iron-mining days before coal replaced charcoal in the smelting process.

Also among them were a number of previously unknown "scowles", which are fissures in the ground from which iron ore has been extracted, and are a feature almost unique to the Forest of Dean.

A smaller survey of 42 square kilometres (16 square miles) of Savernake Forest in Wiltshire was also carried out to check the accuracy of lidar findings against known archaeological features and veteran trees. This also revealed hundreds of linear and multi-sided features that archaeologists want to check out. And in addition to built structures, lidar is also helping to map the many 'veteran' (very old) trees of Savernake.

Forestry Commission England archaeologist Tim Yarnell explains:

"Archaeologists have used aerial photography for decades to spot the sites of ancient human activity, which become much easier to identify from the air. But the archaeological maps made from aerial photographs always have gaps in them where there is woodland, because conventional cameras cannot see through the trees. It's not always easy to spot features from the ground either, even on open moorland and farmland, but especially so in woodland.

"This has been a great difficulty for archaeologists in general, and for the Forestry Commission in particular. That's because although we manage more scheduled ancient monuments than any other land manager in Britain, as well as thousands of other important features, there are undoubtedly many other archaeological sites in our woods and forests that we don't know about yet or which have been forgotten with the passage of time. Indeed, many archaeological features survive in woodland because they have been forgotten, or they've been protected by the woodland from being destroyed by intensive agriculture or development. These sites represent the history of woodland management and other land uses.

"Lidar technology gives us a wonderful opportunity to discover or rediscover some of these sites and, where appropriate, take steps to look after them and perhaps promote them to the public as places where they can learn more about our ancestors and their rich history. It can open up a whole new world to archaeology."

Meanwhile, lidar has other practical uses in forestry. Foresters can use it to accurately map forests in a way that distinguishes trees of different heights and ages (including 'veteran' trees). It can also inform harvesting plans, and it can show up forest tracks, drainage ditches, timber extraction routes and many other features. This information can be visualised in three dimensions to improve forest management activities, including the planning of operations such as harvesting, thinning and the construction of walking and cycling trails. As Tim Yarnell explains:

"It's one thing to find an archaeological feature, but its conservation and interpretation present new challenges. Lidar technology makes it much easier for our planning foresters to do things such as identify the size of features and plot footpath routes to the archaeological sites, because it can enable them to 'see' the forest floor so clearly."

Furher information about the use of lidar in forests is available from http://www.forestresearch.gov.uk.


"No job worth doing was ever done on time or under budget.."
Khufu
For really I think that the poorest he that is in England hath a life to live, as the greatest he
Thomas Rainborough 1647
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#2
I was trying to get this done on an big commercial project, but everyone baulked at the expense (I would be interested to know exactly how much it costs to do if anyone has the info). I believe there are some good Lidar results from the West Heslerton project as well.
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#3
Good results from floodplains too.

http://www.tvg.bham.ac.uk/Trent_Soar/index.html

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#4
Apparently the Environment agency hold all Lidar data but are unwilling to release it. This may not be true across the board but is certainly true in my region. I am trying to get it using the infromation sharing central gov. guidelines
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#5
The EA only holds the lidar data that they have flown and paid for, and it usually only covers rivers and floodplains. You can get hold of it but you'll usually need to show something in return - the Vale of Pickering project have a whole list of outputs that'll be of use to the EA.

Getting hold of the data is difficult because although it's held in a central store different bits were paid for by different regions, and they technically own it. Your best bet is to get hold of your areas EA archaeologist and enthuse to them about your project - see if they can set some wheels in motion.
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#6
Getting hold of EA LiDAR data is quite easy. All they ask for is for a request for upto 4 tiles for resarch reasons only, no commercial activity. onces you have requested the data, they send you some forms, you fax them this and they they send you there LiDAR data.
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