What is Lidar technology and how does it work?

LiDAR (Light Detection And Ranging) is a remote-sensing technique. It uses pulsed laser light to measure distances and build accurate 3-D maps (point clouds) of objects and surfaces. It is the optical counterpart of RADAR.

Main components: a pulsed laser source (usually near-IR, 905 nm or 1550 nm, or green 532 nm for water), a scanner (rotating mirror or polygon), a photodetector/receiver with a telescope, a precise timer, and GPS + IMU (inertial measurement unit) for position and orientation when airborne. A computer processes the data.

Working:

  Laser --pulse--> [scanner] -------->  target
  Detector <-------- reflected pulse  <--
  timer measures round-trip time t  ->  d = c t / 2

1. The laser emits very short pulses (nanoseconds long), up to hundreds of thousands per second.
2. The pulses strike the target and are scattered or reflected back to the receiver.
3. The time of flight \(t\) is measured, and the distance is \(d=\dfrac{ct}{2}\).
4. The scanner sweeps the beam across the scene. Combining each range with the beam direction (and the GPS/IMU position) gives the x, y, z coordinates of millions of points, which form a 3-D point cloud.
5. The return intensity, multiple returns (for example canopy and then ground) and Doppler shift can also be used to classify surfaces or measure velocity.

Applications: autonomous vehicles (obstacle detection), topographic and forest mapping, archaeology, flood modelling, atmospheric studies (aerosols, clouds, wind), mining, construction and smartphone depth sensing.

Advantages: high resolution and accuracy (cm level), works day and night, can see through gaps in vegetation, and collects data quickly.