It is a relatively new active remote sensing technology using a laser scanner, Global Positioning System (GPS), and inertial navigation. In the same way that SONAR using sound waves and reflection to detect targets and determine distance (think of the ping in the submarine scene from your favourite war movie), LiDAR uses laser pulses with their timed reflectance to determine the target distance. With airborne LiDAR, the target is what lays under the aircraft – be it power lines, vegetation, or the ground.
The standout feature of LiDAR is its ability to see the ground through trees and heavy vegetation. While not passing through vegetation, if the laser pulse can find its way past the leaves, branches, and undergrowth to reach the ground, it can reflect back to the sensor and distance measured. Repeat this process up to 1,000,000 times per second and you can quickly and accurately build a point cloud of target reflections in 3D XYZ space.
Processing of the point cloud allows the ground returns to be identified, from which a model of the ground surface under the forest canopy can be developed. With the relevant flight and survey planning, along with GNSSS post-processing, cm levels of precision can be derived without touching the ground.
This makes LiDAR ideal for surveys in difficult or complex terrain with little access, heavily forested areas, or even regions where it is not safe for a ground survey crew to operate in. In addition, many LiDAR survey vendors offer a co-mounted high resolution digital camera. This provides contemporaneous geo-referenced imagery of your project area along with LiDAR data.