LiDAR

LiDAR

Unmanned aircraft systems (UAS) or vehicles (UAV) at an accessible price are ready to take off for the surveying and geospatial professions. Of particular interest to forest operators, UAVs are very useful for forest surveys.

For example, digital surface models and orthophotos can be created from UAV images of regrowth areas within a cutblock. Height and spatial variations and other tasks can be completed, including: Cruise plot grid creation; Sample areas selected and buffered; Individual Trees selected for height calculation; and, Tree species identification.

In practice, a laser device is attached to a drone, which is then flown above the designated area through which, for example, a utility company wants to build a power line. The laser beams scan all the surfaces below, while the built-in software communicates all the information to the company network. The softwares interpret the collected data and start picturing 3D images of all the objects the laser has detected. These 3D objects can be classified to a variety of different categories, such as buildings, trees and even the trees that are in risk of falling down.

UAVs or a UAS can provide tangible benefits, particularly in speed, safety, and efficiency. Several companies appear prepared to lead surveying and the geospatial community into the air with unmanned vehicles.

Planning the corridor clearance in an object-specific way makes the actual clearing more logical and logistically practical. This results in the most cost efficient path through the vegetation, while avoiding all obstacles that put the power line under any serious risk of future malfunction.

The benefits drive the acceleration of UAS usage, and the benefits start with speed.

“Speed is significantly greater than what a surveyor can do with traditional tools,” said Rob Miller, the UAS portfolio manager at Trimble, a  UAS mapping solutions provider based in Belgium.

In their abstract “UAV LiDAR for below-canopy forest surveys”, published November 2, 2013 in the Journal of Unmanned Vehicle Systems, a group of researchers from Singapore explain that remote sensing tools are increasingly being used to survey forest structure.

Automated Survey Vehicles

“Most current methods rely on GPS signals, which are available in above-canopy surveys or in below-canopy surveys of open forests,” say abstract authors Ryan Chisholm, Jinqiang Cui,  Shawn Lum, and Ben Chend. “But these may be absent in below-canopy environments of dense forests.”

The researchers trialled a technology that facilitates mobile surveys in GPS-denied below-canopy forest environments. The platform consists of a battery-powered UAV mounted with a LiDAR system. It lacks a GPS or any other localisation device. The vehicle is capable of an 8 min flight duration and autonomous operation but was remotely piloted in the present study.

They flew the UAV around a 20 m × 20 m patch of roadside trees and developed postprocessing software to estimate the diameter-at-breast-height (DBH) of 12 trees that were detected by the LiDAR. The method detected 73% of trees greater than 200 mm DBH within 3 m of the flight path. Smaller and more distant trees could not be detected reliably. The UAV-based DBH estimates of detected trees were positively correlated with the human-based estimates  with a median absolute error of 18.1%, a root-mean-square error of 25.1% and a bias of -1.2%.

The authors summarise the main current limitations of this technology and outline potential solutions. The greatest gains in precision could be achieved through use of a localisation device. The long-term factor limiting the deployment of below-canopy UAV surveys is likely to be battery technology. The full report can be found here: http://www.nrcresearchpress.com/doi/pdf/10.1139/juvs-2013-0017

UAS also offer advantages in safety, particularly in difficult terrain and for avoiding wildlife and snakes in land surveying. Perhaps most importantly, UAS provide great benefits in efficiency, saving time and money for firms on many projects.  “Just the fact that you can do things cheaper, you can do things yourself and you can do things on demand and get 100 times better resolution, it’s become a very attractive thing,” says Pat Lohman, the COO of Precision Hawk, a UAS company that was founded in Canada.

Precision Hawk has ventured into other applications, such as infrastructure surveying and 3D topographical modeling. The company used its Lancaster UAV platform to help CP Rail in Canada construct a 3D topographic model of a stretch of railroad tracks hugging the base of a cliff near Lake Superior. Working with Queen’s University, CP Rail has tried to determine when rocks will fall on the tracks. The project is dangerous, and it’s costly for manned aviation because it involves photographing just 1,000 feet of cliff.

Finnish utility companies have for a long time had difficulties in finding more efficient ways of clearing pathways for power lines through the dense and spread out forests of Finland. Traditionally, this would require a good deal of manpower and extremely costly helicopters, who would manually observe, calculate and analyse the possible routes. Hours of hard work would then be under risk of being overturned by a wind gust blowing a weak trunk over the completed power line.

Helsinki-based Sharper Shape is already bringing a new approach to forest surveying, which is vital for Finland’s electricity grid. But its founders also want to be the top vendor of intelligence systems for drones—and not just in Finland. Sharper Shape wants to put a brain in every unmanned aerial vehicle worldwide.

With such dense and extensive tree growth, laying down power lines in the most efficient manner possible—avoiding trees without making the line longer than it needs to be, choosing which trees need to be removed, and so on—requires extensive land surveying. Helicopters are used to speed up the job, but that still requires a lot of man hours, both to fly the vehicles and to collect and analyze the data. By using laser scanning systems, UAVs and UAS have made the job a little easier.

In current practice, a Sharper Shape laser device is attached to a helicopter that flies over the forest to be surveyed. As the onboard lasers scan the ground and plot trees and other objects in 3D, software interprets the data to categorize each object in real-time. The system then analyzes the data about the forest to provide the most efficient locations for laying power lines. The software can even distinguish between a healthy tree and one that might fall down—that’s vital, as a dead tree could easily fall on a power line. The laser will eventually allow Sharper Shape to ditch the helicopters in favor of unmanned vehicles.

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