Lidar (Light Detection And Radar) is a photonics technology based on laser. Mounted on an aircraft Lidar technology is able to create maps of extremely high detail. The Lidar sensor sends invisible near-infrared light pulses to the ground. The distance is then calculated by recording the time the light pulse takes to travel from the sensor to the ground and back.
By emitting hundreds of thousands of light pulses per second, the precise geometry of the earth can be measured from the points of reflection. This is how a ‘point cloud’ is generated. The higher the number of points, the denser and more realistic the 3D model is.
Traditionally, large swathes of land are captured by flying aircraft at great heights. This means point density is reduced, producing results as low as 3-5 points per square metre. The method is used for measuring tree height in a forest, for example. But the end result is a surface that lacks detail.
Airborne Laser Scanning (ALS) is able to generate higher density data by flying lower and using the latest LiDAR technology. The picture shows a pointcloud collected by installing a LiDAR application called ROBIN+WINGS in a manned helicopter flown 100m above ground.
Because helicopters can fly low and slow, a greater number of pulses can be bounced back and forth, collecting a greater number of measured points on the ground. For this particular project, point densities of 600pts/m2 were recorded, resulting in an extremely detailed pointcloud (see picture).
For more information go to the website.
Want to know more about Lidar applications, look at the program of the Photonics Applications Week.