The work carried out in the forest was based on barely visible changes in the forest floor that were revealed using detailed LiDAR surveys. The first was carried out by Gloucestershire County Council and Forestry Commission in 2012.
What is LiDAR?
LiDAR stands for Light Detection And Ranging and is a technique that is a remote sensing method using light in the form of a pulsed laser to measure ranges (variable distances) to the Earth.
The use of LiDAR in forestry surveying is explained nicely in a Journal of Forestry article entitled “Lidar Remote Sensing for Forestry”
How does LiDAR work?
Laser pulses are emitted from a device attached to a vehicle such as a plane. The laser pulses create a topographic map similar to how a bat uses echolocation. The light shot down from the plane bounces off objects below (leaves, branches, trees, rocks, etc.), returning to hit a detector on the bottom of the plane. The device then calculates where the object is using satelites to help work out the height of the emitter from the ground, the height of the receiver from the ground, and the time it took to receive the reflected pulse – which gives the distance from the emitter – and the precise location of the object.
As the pulse hits a leaf, flower or branch, the time taken will be less than if it hit the ground and so as the survey progresses in a grid across an area and back again, it is able to establish what is most likely to be solid (like the ground or a structure) and ignores the rest.
