Flying in the Celtic west

Peter Rauxloh

Around 2,500 years ago the Deceangli tribe controlled north-east Wales, and it is they who were probably responsible for the construction of a string of six fortified enclosures on the Clwydian Range and LLantysilio Mountain. All the forts consist of multiple lines of banked defences, along with powerful in-turned gateways. They range in size from the smallest at just three acres called Moel y Gar, Llantysillo, to the largest, Penycloddiau (Pen-clod-e-i),  which at 50 acres is one of the largest hill forts Wales.

The landscape’s special character was recognised in 1985 by the creation of the Clwydian Range Area of Outstanding Natural Beauty. The number of visitors to the mountain heaths increased the risk of habitat damage and in response to this, and the need to promote conservation and public enjoyment, the Heather and Hill forts Landscape Partnership Scheme was started in 2007.  Archaeological research has been central to the many project carried out under the scheme, and it is in support of the archaeology department of Liverpool University at Penycloddiau,  that we flew our Small Unmanned Aircraft over the site in August 2015.

Comprising a North West/ Sout East aligned circuit of banks, some 800m long and 400m at its widest point, the fort drops 50m in height from the massive multiple banks at the northern end to the interned entrance ramparts at the southern tip. The elongated nature of the site coupled with a strong wind blowing diagonally across its (the sites lies c.440m above sea level) required an ingenious flight plan to capture the imagery accurately. 

Since the aircraft must fly in a regular grid pattern, we need to turn into the wind at the end of each leg rather than with it. Equally, since the overlap between one image and the next images must be maintained around the magic 80% mark, and because that overlap is directly proportional to speed, we need to keep a constant speed.  We therefore fly across the wind, since flying directly into it will lead to great variation in speed on each leg of the survey.

Nine ground control targets were laid out and their position accurately recorded, with the flight then being completed in about 30mins of flying time. The data was processed in Agisoft Photoscan with the resultant detailed 2D orthomosaic and 3D model being made available immediately to the researchers using the Dronelab (2D orthomosaic) and Sketchfab (3D model) web services. These are best viewed in the Chrome browser.

The survey was a rapid means of capturing detailed two and three dimensional data over a wide area, providing both excellent baseline data for research and managment purposes and an immersive presentation of the monument, which could be a valuable asset for the promotion of the area and its incredible heritage.

If you wish to know more about our aerial survey please follow the links below or contact Dr. Peter Rauxloh.

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