18.04.2018 | LIDAR technology enables the efficient surveying of overhead power lines across great distances

"Painting by numbers" using helicopters and lasers

IWB (Industrielle Werke Basel) has commissioned Axpo to survey its 100-kilometre long overhead power line grid. Data is recorded, classified and documented by means of innovative LIDAR technology using helicopters and laser scanning. 

The rotors are turning faster and faster: The helicopter takes off with heavy cargo on board. The pilot flys an exact route along the overhead power line. This enables the survey of IWB's entire 100-kilometre, 145-kV grid in just one day. However, the relatively short flight involves lengthy, meticulous preparation beforehand. The flight must be carefully planned because speed and height play an important role in surveying. In addition, the space-consuming laser device must be installed before take off. In this innovative process, data is recorded by means of LIDAR technology (light detection and ranging). When the flight ends, the real work begins. The Axpo project team must convert the recorded and classified data into line models and put the information down on paper.

The survey data is displayed and monitored during the flight. (©BSF Swissphoto)

LIDAR technology is installed before the flight. (©BSF Swissphoto)

No room for passengers: Hardeware and software are on board. (©BSF Swissphoto)

During the flight with LIDAR technology, lasers do the surveying. (©BSF Swissphoto)

From the point cloud to the line model

The advantages of the laser scanning process are obvious for Patrik Schönenberger, Axpo Technology Project Specialist: "With this method, it is possible to survey power line grids across long distances in a short time. LIDAR achieves a precision of 5 cm in height and 10 cm in length. Manual (terrestrial) surveying is more precise with 1 mm. However this method involves a great deal of effort and is better suited for individual objects, for example a power line mast, rather than for long distance surveying." Where necessary, terrestrial surveys can be carried out in addition to laser scanning in order to check details.

How does the LIDAR method work? Axpo Project Manager David Bugmann makes an excellent comparison for the data processing method with LIDAR: "It's kind of like painting by numbers. First data is recorded by means of laser scanning – through the light irradiated back from the atmosphere during the flight. A large point cloud is created. Subsequently data is vectorised so that the points can be connected and the line become visible. In the last step, data is verified with software. The lines are reconstructed with digital models and checked to see if they fulfil legal specifications." The complete power line data provides information on whether the legal requirements such as ground clearance or the distance to buildings have been adhered to.

This video shows how the data is processed:

Important outside market business

The 100-kilometre long, 145-kV power line grid belongs to Industrielle Werke Basel (IWB). Its old planning documentation, some of it going back to the original construction period, had to be reviewed. In a public tender process, Axpo was awarded the contract for IWB's "Survey technology overhead lines" project last year. The innovative, efficient flight approach convinced the contractor. The project includes the survey of the entire overhead line grid with laser scanning, as well as re-routing and documentation.
 
Complementary to its own long-standing know-how in the area of grid surveying and construction, the project team enlisted the help of BSF Swissphoto for the LIDAR flight. The Swiss-German company is at home in the geodata industry and provides helicopter surveying among other services.

At the end of 2017, the documentation of one of the two power line grids (some 100 kilometres) was completed and submitted to IWB. David Bugmann and Patrik Schönenberger would like to go along on the second helicopter flight over the power lines: "That would be really great," they agree.

David Bugmann, Project Manager Line Construction, in the field.
Patrik Schönenberger carring out a terrestrial survey with a theodolite and combined GPS sensor/reflector.

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