#A2ZChallenge L is for #LiDAR

L is for LiDAR

Theme: Ancient Roman Scotland during the Flavian era

LiDAR (Light Detection and Ranging) isn’t a brand new technology but it’s an extremely useful development for archaeologists. 

Till relatively recently archaeologists have depended on ground investigations, specialist identification tools for that improving greatly as geophysics and other ground penetration techniques have become more sophisticated, and affordable. 

Aerial surveying has been really important for archaeological pinpointing of potential sites since approximately post-World War II (though used before then for various reasons both military and civilian). Satellite imagery has also been selectively used since perhaps the 1980s for archaeological reasons, but using both of those survey results must also go hand-in-hand with ground investigations. And more recently DRONE aerial surveying is providing some clues at specific sites for archaeologists to investigate. 

Click  HERE for information on Aerial surveys. I totally recommend the FutureLearn -Hadrian's Wall course that this comes from since I did the course a couple of years ago! 

LiDAR is another identification-of-sites tool for archaeologists to use - so long as their budget can stand it. Where aerial surveying produced physical photographs of the land below the fixed wing aircraft or the helicopter, LiDAR can do so much more. 

In Scotland, the aerial photography results from some particularly dry summers produced really great images of potential Ancient Roman encampments, especially in northern Aberdeenshire. From 1976 onwards, some wonderful sites have been identified, like the huge encampment at Durno opposite the hill range of Bennachie. There is nothing visible at the Durno site but the sheer size of the perimeter of the encampment indicated a huge army of around 30,000+ soldiers could have been sheltered there. Only small sections of the perimeter were investigated so dating it to Agricolan or Severan use was difficult. Because of the size at 58 hectares, the largest camp in northern Scotland, it was thought to have been used by Emperor Severus in c. AD 210 but a re-use of an Agricolan site from AD 84 isn’t to be discounted.

 

1976 (Canmore)

Aerial photographs can indicate disturbances to the sub-soil, which show up as dark shadows, or hazy marks on tilled areas. Where the soil has been disturbed in past centuries at certain depths beneath ground level, the rate of absorption of water (from rain) differs from undisturbed areas and that’s what shows up darker – outlines of Neolithic use, Iron-Age roundhouse construction, or Roman camp ramparts, holding the moisture longer than the other soil which dries out much more quickly. 

In the aerial photograph here the current field areas have definite boundary areas. However,  from bottom middle there is a slightly lighter line which heads left and slightly upwards leading to  a rounded corner where the line then goes directly upwards with a definite break in the line. This would be interpreted as most likely being the outline of an Ancient Roman Temporary camp, the break in the line being one of the camp gates. Ground inspection of the marked area would then be needed to attest the site as used by the Ancient Romans. 

The main drawbacks to Aerial photography are that it really only works well during very dry summers (northern Scotland has few of those) and it can’t show soil disturbance indicating pre-historic/early use of the areas in areas of heavily wooded landscape.

That is where LiDAR is making an immense difference in archaeological surveying. LiDAR can be used in heavily forested areas since the laser beams can detect disturbances to the ground even in forested areas and areas where crops are not grown in Scotland, as in heather clothed hillsides and scrubland.

Now that computers have become so efficient, the sending of literally millions of laser beams down to the ground from an aircraft is easily possible. Onboard computers collect those ‘millions of data images’ and process them, producing a scan like image of the ground below. The most important thing about LiDAR is that those beams penetrate even the densest of Aberdeenshire forests and skilled interpreters can identify possible sites of archaeological interest. Used in conjunction with GPS (Global Positioning Systems) finding the identified area is possible now, even when deep in a forest.

For more information on LiDAR click HERE 

Much of Scotland is presently clothed in heavily wooded areas though almost none of that is Ancient Caledonian indigenous forest. Much of the forestry visible today has been planted either by owners of the huge estates since the 1700s or by The Forestry Commission which was set up in the early 1920s. There could easily be many traces of Ancient Roman activity under the soil in some of those wooded areas and that’s what’s very exciting about the latest use of LiDAR!

I await with bated breath for any new information from either aerial or LiDAR surveys that will enhance knowledge of the invasions of General Agricola in Scotland during his campaigns from c. AD 78-84.

Till Monday, and another #A2ZChallege post…

Slainthe!

            `           `