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The Basics of LiDAR

AUTHORS: Leah A. Wasser

How LiDAR Works

LiDAR is an active Remote sensing system. An active system means that the system itself generates energy - in this case, light - to measure things on the ground. In a LiDAR system, light is emitted from a rapidly firing laser. You can imagine light quickly strobing from a laser light source. This light travels to the ground and reflects off of things like buildings and tree branches. The reflected light energy then returns to the LiDAR sensor where it is recorded.

A LiDAR system measures the time it takes for emitted light to travel to the ground and back. That time is used to calculate distance traveled. Distance traveled is then converted to elevation. These measurements are made using the key components of a lidar system including a GPS that identifies the X,Y,Z location of the light energy and an Internal Measurement Unit (IMU) that provides the orientation of the plane in the sky.

How Light Energy Is Used to Measure Trees

Light energy is a collection of photons. As photon that make up light moves towards the ground, they hit objects such as branches on a tree. Some of the light reflects off of those objects and returns to the sensor. If the object is small, and there are gaps surrounding it that allow light to pass through, some light continues down towards the ground. Because some photons reflect off of things like branches but others continue down towards the ground, multiple reflections may be recorded from one pulse of light.

How Scientists Use LiDAR Data

There are many different uses for LiDAR data.

· LiDAR data classically have been used to derive high resolution elevation data

LiDAR data have historically been used to generate high resolution elevation datasets. Source: National Ecologica Observatory Network .

· LiDAR data have also been used to derive information about vegetation structure including

  -Canopy Height

  -Canopy Cover

  -Leaf Area Index

  -Vertical Forest Structure

  -Species identification (if a less dense forests with high point density LiDAR)

Cross section showing LiDAR point cloud data superimposed on the corresponding landscape profile. Source: National Ecological Observatory Network.

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