Category: Image Processing

LiDAR

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Measuring without boundaries

LiDAR is a technology that is similar to RADAR. LIDAR stands for Light Detection And Ranging. In RADAR, antennas emit sound waves of suitable frequency and wavelength. The sound waves travel through the medium, reflect off an obstacle, and the detectors receive these waves. The distance from the block is measured using the time interval between emission and detection and sound speed. Similarly, we use laser light in LiDAR rather than sound waves.

LiDAR uses the ultraviolet, visible light, and near-infrared radiations of the electromagnetic spectrum. The wavelengths of these radiations range from 10 micrometers to 250nm. The reflection of light from the obstacle is not similar to the pure reflection from a plane mirror. The light then reflects via backscattering. Different scattering types such as Rayleigh scattering, Mie scattering, and Raman scattering occur based on the application.

LiDAR technology is utilized to measure distances and is also used to map and construct 3D images of objects. One of the 3D imaging LiDAR technology is called Flash LIDAR.

The basic formula for calculating the distance from the obstacle is: Distance = (Speed of light * Time of flight)/2

Components of a LiDAR system:

  1. Laser source and detector: The laser source is the component that generates the energy of a suitable wavelength. The detector is the component that detects the laser light that is reflected/scattered back from target objects.
  2. Timing electronics: It is the component that measures the time interval between laser emission and detection. It must be very accurate to obtain accurate results.
  3. LIDAR also consists of a Global Positioning System (GPS) and Continuous Operating Reference Station (CORS). These systems correct and improve the accuracy of the data obtained by the sensors.
  4. Inertia Measurement Unit (IMU): It is used in LiDAR systems in aircraft. It contains various components such as accelerometer, gyroscope, and magnetometer sensors that measure the velocity, orientation, and gravitational forces. It is used to measure the pitch, roll, and yaw of the aircraft.
  5. Computer: A specialized computer system is used to integrate and process the other components’ data and produce the output.

Applications:

  • Autonomous Driverless Vehicles: LiDAR is used in autonomous vehicles for obstacle detection. In certain vehicles, 360 degree rotating LiDAR devices are used to check for obstacles in all directions. It can be imagined as something similar to an ambulance siren producing laser light. Since the LIDAR devices are placed at the top of the vehicles, it is necessary to ensure that the laser light does not damage human eyes. Hence 1550 nm lasers are used as this wavelength is not strongly absorbed by the eye.
  • Biodiversity: Airborne LIDAR systems are used to measure canopy heights and measure leaves’ surface areas. It is also used to study the biodiversity of plants, fungi, and animals.
  • Law Enforcement: A LIDAR speed gun is used to measure vehicles’ speed and enforce over-speeding fines on drivers. It is also used in crime investigations and forensics, such as detecting the speed of a bullet.
  • Games: LIDAR is used to take a survey of road conditions, and the 3D image generated by the system is used to simulate the road for simulation racing games. The road surfaces are replicated with a centimeter or millimeter precision.

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