LiDAR stands for Light Detection And Ranging, and a LiDAR survey is carried out by specialist equipment, from an aeroplane. The plane makes a number of passes over the chosen area, directing laser pulses at the ground. The principle is similar to RADAR, except LASERS are used to bounce light off the ground instead of using radio waves.
The survey is done when the broadleaf trees are devoid of leaf cover and the understorey vegetation is at a minimum, with two sets of data from the LASER pulses. The first return shows the height of the vegetation and the second return goes past the vegetation to hit the ground.
LiDAR data can be processed to show different views. When the data is processed, a Digital Terrain Model (DTM) can be produced, filtering out the vegetation to give a clear picture of the topography of the area, showing contours, ditches and banks; very useful for highlighting archaeology. Colour ramps, where different colours represent different heights, are used to highlight features, allowing a 2D image to represent 3D data. Another technique makes it possible for it to appear as though the light is shining from different directions, to show shadows.
A Digital Surface Model (DSM) can also be produced, using a colour ramp to show different heights of vegetation, which can be used for mapping trees and vegetation. This data is very useful for informing conservation management plans.
In spring 2010 a LiDAR survey of the Blean was undertaken, thanks to a Heritage Lottery Fund grant through Kent Wildlife Trust’s Blean Project, with extra funding provided by Blean Initiative partners so that the survey could cover the whole area. Follow the link in the menu to the left to view the Digital Terrain Model of the Blean complex and surrounding area.
Kent Wildlife Trust