Using UAV LiDAR to locate, identify and preserve old trees

UAV LiDAR has many different applications – this one was specialist to protect the next generation of ancient trees. Using the Routescene UAV LiDAR system the FlyThru team surveyed a potential building site, to establish the position and size of all the trees within the location, the results of which were used to inform which trees would remain and which would be cleared. Through this project many trees that have stood for over a hundred years were saved for protection.

Overgrown site earmarked for housing development

In August 2019 the FlyThru team were instructed by WYG Environmental and Planning to survey a site at the Old Water Pumping Station at Whitley, near Coventry in the UK. The side is jointly owned by two companies which had plans to develop the site for housing. The area was extremely overgrown with dense willow, bramble, as well as mature and well established deciduous and conifer trees, some of considerable size.

The aim of the survey was to identify trees with a trunk diameter in excess of 100mm. The results of the survey would enable a site clearance plan to be developed.

Old Pumping Station Site
The site

Preparing the site

Once access was gained to the site, ground control was established. The LiDAR survey was straightforward and performed in three overlapping surveys. Photogrammetry was also gathered on the same day. Coventry Airport was also helpful with their approach to UAV’s flying within their no-fly zone with their permission.

Flight planning LiDAR survey Old Pumping Station
Flight planning

Using LiDAR to locate and size trees

Due to the dense tree and vegetation coverage across the site it was clear that the best survey technique to deploy was a LiDAR system on a drone. The team used the Routescene LidarPod on their rotary UAV (unmanned aerial vehicle) flying at an altitude of 40m over the site. The 32 lasers within the system scan at a rate of over 1.4 million points per second. These lasers can penetrate through the different layers of vegetation from the top of the tree canopy down to the ground, achieving over 400 hits (known as points) on the ground per square metre, enabling the easy location and sizing of each tree.

Routescene LidarPod mounted under the drone
The Routescene LidarPod mounted underneath the drone

The resultant point cloud data was post-processed in LidarViewer, the specialist LiDAR software developed by Routescene, to create detailed contour maps and calculate the basal area of each tree. The detailed contour maps enabled the developers to understand the varying ground levels across the site, which were difficult to ascertain with the naked eye due to the thick undergrowth.

Combined LiDAR and photogrammetry data for tree identification

To enable the arboriculturists to identify individual trees by species the foliage and canopy shape can be assessed. The FlyThru team collected UAV photogrammetry at a height of 60m. The powerful combination of these high definition images with the high resolution LiDAR point cloud allowed the tree identification task to be rapidly completed.

 

Ground set up near the Old Pump Station
Ground set up near the Old Pump Station showing dense brambles

Processing the data

The FlyThru team carried out considerable data processing to locate the trees as seen in the diagram below.

Location of trees at LiDAR survey Old Pumping Station
The location of the trees

Summary

This case study shows the value of UAV LiDAR for planners wishing to develop an overgrown site for building development. Using a combination of UAV LiDAR and photogrammetry the FlyThru team were able to work quickly and efficiently without disturbing the ecology, to help preserve trees over a century old. Creating a contour map of the heavily vegetated site, using the LiDAR data, highlighted that considerably more soil would need to be removed than had been initially estimated to make the site level. As a result the client was made aware of this additional task and cost much earlier.

Michael May from FlyThru commented “Using LiDAR on a UAV was an extremely efficient surveying methodology in these conditions. UAV LiDAR is ideal in areas of dense vegetation. It would have taken a considerable amount of time to survey the overgrown site by conventional means. This project showcases the benefits of using both UAV LiDAR and photogrammetry survey methods together to produce detailed and definitive results.

For more information on the Routescene UAV LiDAR system click here

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