Blom has been commissioned by the Swedish Transport Administration to conduct an inventory of hazardous trees along one of the power lines supplying the Swedish railway network with electricity. All trees that within 8 years of growth may fall on the power lines have been identified and compensation calculated under current forestry standard. The inventory is made entirely from a helicopter-based laser scanning and aerial photography.

In conjunction with the Transport Administration needed to produce a 3D digital map of the transmission line it was also made an inventory of hazardous trees, fertilize mapping, digitization of power line area width and zoning of vegetation blow the power line including mean height and density class. Since laser scanning is done with a very high density ensures that all objects in the vicinity of the power line are measured in high precision.

- Nothing is left to chance, every inch is covered at 100% of the laser beams. Data collection is followed by a quality check were the reached the point density is controlled. It will appear if any area should be in lack laser points, says Peter Östrand who has extensive experience in infrastructure and now works with data collection at Blom.

Laser scanning provides precise elevation measurements on individual trees and by age and site productivity growth is estimated for 8 years. All trees that within this period may fall within 2m from the line are considered hazardous and are mapped in stereo aerial photographs so that tree species, size and position can be specified. Often it is only a few trees that are identified but sometimes entire areas need to be felled. Finally, a compensation calculation under forest standard is conducted of each individual tree.

- It is clearly seen how the previous field inventory has missed a number of trees that have been able to fall in power line for a long time. However, it is not a given that we will find more trees than what had been done in a similar field inventory because we can also be certain of the trees that cannot reach the power line, says Martin Sjödin who is working with the current project at Blom.


Blom has developed a method for calculating compensation payments according to standard procedures, which often is current at the expropriation of forest land.

For more information, please contact Martin Sjödin, phone: +46 (0)70 836 45 75 or email: martin.sjodin@blomasa.com

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