The coal industry has left an indelible mark on the culture of the United Kingdom. Entire communities are still defined by their connection to the pits and deep rifts in the political landscape persist to this day over the handling of their closure in the second half of the last century.
Mining has also left a very physical legacy as well, in the warren of underground tunnels crisscrossing much of the country. There are more than 115,000 abandoned mineshafts that are known about and potentially many more undocumented ones.
The UK Coal Authority was established in 1994 to take over responsibility for licensing coal mining operations and providing information on coal reserves from the state-owned British Coal Corporation. But with the demise of the domestic industry its role has increasingly shifted to managing the industry’s aftermath including subsidence, water pollution and the dangers posed by abandoned shafts.
Many of these abandoned shafts on publicly accessible lands, which means providing accurate and up to date safety information is essential to prevent accidents involving members of the public.
Traditionally the Coal Authority has sent its inspectors out on foot to map the locations of these shafts and monitor them over time using standard surveying equipment such as GPS and total stations. But with many of these shafts overgrown with vegetation and partially collapsed, the inspectors face the same risks as members of the public.
“They were having to send out inspectors in twos for safety reasons because they were literally falling down holes that were covered over with vegetation and hidden from ground eye level view,” says Mark Hudson, co-founder and managing director of SLS Coastway Surveys, a firm of chartered land surveyors and geospatial engineers hired by the Coal Authority to find a safer way to map these shafts.
The firm was founded in 1999, but about three years ago Hudson decided to invest in the emerging field of drone technology. Using an unmanned aerial vehicle (UAV) allows the firm to cover huge tracts of land in a fraction of the time it would take to do so on foot and at a significantly lower cost than more established aerial surveying methods using planes or helicopters.
Being a specialist in sub-surface and mining surveying and having previously worked as a surveyor for British Coal, Hudson had plenty of connections at the Coal Authority and when they heard he was diversifying into drone technology they were keen to see what he could offer.
To test the principle, in 2012 Coastway were asked to map more than 100 hectares of land at Axe Edge Moor in Buxton, which was mined from around 1600AD until activity was abandoned early in the 20th Century, leaving roughly 500 known abandoned mine shafts. Using a senseFly swingletCAM fixed-wing UAV together with GPS they surveyed the site in roughly 30 minutes – a fraction of the two days it would have taken to map it on foot – with a much higher accuracy and none of the associated dangers.
Using mapping software from Pix4D Coastway combined the GPS data with the digital photographs taken by the drone to create orthorectified photography maps – where images are corrected to take account of camera tilt, topography and lens distortion to give true distances – and a digital elevation model of the site that mapped both existing shafts and located previously unknown ones.
The Coal Authority was so impressed with the work they have now entered into a long term partnership with Coastway to monitor six sites across the country on a regular basis. “We’re doing quite a bit of work with the Coal Authority now, also looking at subsidence events in areas where there’s been historic underground coal mining,” says Hudson.
Not wanting to stand still, the firm has since upgraded their equipment several times, first by purchasing senseFly’s more recent eBee drone and then upgrading to the specialist surveying model, which features real time kinematic (RTK) satellite navigation that increases the precision of positional data down to the centimetre level.
“The biggest problem we found with the swingletCAM and the standard eBee was having to put ground control points to produce accurate ground surface models and that takes time and requires more men on the ground,” says Hudson. ““Now we’re upgrading to an RTK fixed wing UAV and we will not have to put in extensive survey ground control points. We will still put a few in for redundancy but it’s a lot, lot quicker with an RTK UAV.”
One issue with using photography based surveying, though, is the inability of cameras to see through dense vegetation. This means the images produced are not a true representation of the area’s ground surface topography – a problem Coastway has encountered regularly when working with the Coal Authority’s overgrown mineshafts.
To resolve the issue the firm teamed up with Aberdeen-based surveying equipment company Sabre to create a bespoke UAV capable of carrying a LIDAR system – technology that bounces laser light off objects to build up a picture of the surroundings in a similar way to active radar – which is capable of producing far more accurate survey data.
“We always try and keep ahead of the game and innovate and work with partners who are at the cutting-edge of new UAV R&D. That’s what led to the development of the heavy lift LIDAR drone with Sabre,” says Hudson. “The drone has been designed from scratch using the best technology available, but it’s pretty huge, it has to be, to lift a FARO Focus 3D scanner!”
Coastway hopes to start using the drone in the coming months and despite its size the drone is still be under the 20kg limit that allows it to be flown commercially by the UK Civil Aviation Authority (CAA).
All the firm’s drones have been cleared to fly by the CAA and the Irish Aviation Authority (IAA), but according to Hudson the process has not been simple, especially with the CAA. “We had a lot of issues and trying to get something resolved takes a while. Basically everything overruns,” he says. “I think the CAA are literally inundated with people buying quadcopters, who only want to use them for photography and video.”
The project with the Coal Authority is not the only one where the company has been using their drones to carry out surveying work, and since developing their capabilities they have been looking for extra work overseas. While having CAA and IAA approval under their belt already does help, Hudson says a lack of standardisation in drone laws means dealing with regulators can be a varied experience.
“Certain countries are quite relaxed, like Germany; you can fly a drone almost anywhere there. But you go to the Netherlands and it’s a nightmare, almost impossible to fly a drone without masses of bureaucracy. We really need a single policy and legislation for flying drones commercially worldwide,” he says.
But with the use of drones for surveying only just beginning to become mainstream in the UK, there is no shortage of work domestically and considerable similarities between drone imaging software and that used for more traditional surveying has made integrating UAVs into their operations relatively simple.
“It’s been a bit of a steep learning curve for us,” says Hudson. “But I think a big advantage for us is we are chartered land surveyors who started to use drones to benefit our clients, rather than people who have simply got themselves trained up on using drones and have then thought, ‘let’s have a go at surveying’ – a dangerous practice which leads to huge errors in client deliverables.”
With growing demand for UAV surveying and in particular thousands of the Coal Authority’s mineshafts still in need of monitoring, Hudson is confident of making a healthy return on his investment in UAVs. “There are several hundred sites that could be surveyed with our UAV’s. Economics prevail at the moment although safety will prevail on many of these sites in the near future” he says.