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PROJECT NAME: Visual Tunnel Inspection Rotherhithe Station
AREA: South East
SERVICES: Visual Tunnel Inspection at Rotherhithe Station using UAVs
CLIENT: TfL – Transport for London
In July 2019 our company was commissioned by TfL to undertake a pilot project visual tunnel inspection at structure G271 using only Unmanned Aerial Vehicles (UAVs). Structure G271 forms part of Rotherhithe Station on the East London Line at Ch 6700 between Wapping and Canada Water.
Structure G271 was last examined late April 2017 where personnel were restricted to capturing images of the structure from platform level. The report highlighted that due to height restrictions and the station canopies the majority of the structure was out of view. Given the location of the structure, personnel would encounter significant difficulties gaining entry to these areas and be exposed to hazards and the associated risks of working in such areas. The practicalities of attempting to access these areas by traditional methods, e.g., scaffold tower or MEWP, would be very difficult, time-consuming, and costly.
Areas that could not be seen and accessed by personnel were readily reached by our UAV. Elements of the structure that have never been seen before have now been imaged and these images can be used to expand upon previous inspections.
We deployed the DJI Phantom 4 Pro (P4P) quadcopter type drone fitted with a custom-built collision-resistant cage and two “bolt-on” light sources.
The cage encloses the upper half of the P4P, including the propellers but does not obscure the camera’s field of view.
The cage is of robust design and can readily withstand impacts at speeds up to 2m/sec (4.5mph), with no significant effects on the stability and performance of the P4P.
The light sources have variable brightness settings, up to a maximum of 1,500 lumens, giving a combined 3,000 lumens for operating in areas of complete darkness.
The P4P is fitted with an integral 20-megapixel camera with a 1” CMOS sensor and mechanical shutter for instantaneous image capture (electronic shutter cameras collect the image a “row” at a time which can often result in image distortion as a UAV moves in flight).
Images were captured in 3:2 aspect ratio and have dimensions of 5472 x 3648 pixels for maximum viewing resolution.
The UAV flights were undertaken in accordance with our Permission for Commercial Operations, the Operations Manual and the UAV Aerial Survey Work Package Plan. A total of 388No. images were captured during the inspection flights.
We utilise the practice of directed flight in which the pilot is given instructions, on where to manoeuvre the UAV and what to capture images of, by the examining engineer. This entails the engineer observing the camera feed directly and giving precise manoeuvring instructions to the pilot, i.e., move in a particular direction for a certain distance, capture an image etc.
In this instance the engineer is also a qualified UAV pilot, and familiar with the handling characteristics of the P4P and is able to set the camera parameters and capture the images thereby allowing the pilot to concentrate entirely on the flying task, reducing pilot workload, which results in a significant increase in safe operating and productivity.
The application of UAV to visually inspect structures in difficult to access spaces has proven to be practicable in terms of both safety and efficiency when compared to traditional access methods such as MEWP and roped access.
Elements of the structure that were previously unseen have been successfully imaged and numerous defects identified at various locations throughout the tunnel.