Survey of a cliffside road in Kerry

A road under constant threat from the elements

The section of road at Mountain Stages runs about halfway up a very steep hill or cliff. Straight down from the road is the sea; up is the mountain. The area has been monitored for landslides and coastal erosion since around 2015 — an ongoing concern for a road that provides essential access along this stretch of the Kerry coastline.

A drone survey was carried out back in 2018 by a different company. At the time it was considered very modern and futuristic, and it provided low-resolution but useful imagery of the state of the area. That report became the baseline for all subsequent monitoring.

As Bob Foley, founder of Engineers With Drones, explains: "They gave us the previous report and that always helps a lot because it's very, very useful if you're reporting on an ongoing situation to be able to present back to the client like for like so they can say, okay, this is that exact spot. This is the exact same angle looking at this spot. And this is what it looked like five years ago. And this is what it looks like right now."

Replicating history with precision

The main challenge was not just to capture current imagery of the cliffside — it was to capture it from the exact same angles, at the exact same locations, as the 2018 survey. Without that precision, the comparison would be meaningless. A defect photographed from a different angle could look completely different, making it impossible to tell whether the change was real or just a trick of perspective.

The previous report was essential. Engineers With Drones used it to generate an imagery capture plan before even setting foot on site, mapping out exactly where to position the drone to match each historical shot. This preparation meant the fieldwork could proceed efficiently, with no time wasted figuring out angles on the day.

A small drone with three lenses for every shot

The Mavic 3 Pro was chosen for this job. It is a small enough drone that it is not dangerous in open countryside, but it carries three separate lenses — wide, medium, and zoom. That gave the team the ability to capture wide overview imagery for spatial context, and then zoom in on specific defects for detailed close-ups, all from the same flight.

The drone also has excellent video characteristics, and the client wanted video footage of the full 2km section as well as stills. The zoom lens was particularly useful for capturing detailed imagery of erosion features and landslide-prone areas without needing to bring the drone dangerously close to the cliff face.

From previous report to finished dataset

On site, the team captured all the imagery over the course of a single day. The previous report guided every shot — each historical angle was replicated, and additional imagery was captured wherever new defects or areas of interest were identified.

Back in the office, the full dataset was processed and married against the previous report. The 2km road section was divided into smaller sections, and every image was assigned to its relevant section. Where the previous report had annotated defects with specific identifiers, Engineers With Drones applied the same identifiers to the contemporary imagery — making it trivially easy for the client to find the current image of any previously identified defect.

The final dataset was delivered on a cloud platform of the client's choosing.

A stark difference in quality — and a clear picture of change

The difference in image quality between the 2018 survey and this one was very stark. As Bob notes: "Even though the last drone that flew this was about the size of a coffee table, large drone with a big old camera on it, the imagery was relatively low quality when last done. Whereas this one, each image was at least 20 megapixels, very high resolution, a lot of detail, and because all the angles were the same, you can get a lot more idea of exactly what you were dealing with in terms of the coastal erosion, geomorphology, all that sort of stuff."

The person responsible for analysing the imagery and assessing the current state of the road had a much better understanding of the actual topography of the land, and could make a far more informed decision about whether the road was safe to continue using. The client was very happy with the result.

What the client received

Drone footage of the cliffside road survey

Video footage captured during the survey, showing the full 2km section of cliffside road at Mountain Stages and the surrounding coastal terrain.