LiDAR or Light Detection and Ranging can be referred to as a type of active remote sensing system used to measure the distance of an object from the earth’s surface.
LiDAR can also be defined as a method to calculate variable distances by targeting an object or area with a laser and measuring the time taken by the reflected light to return to its receiver.
The system uses sensors to find information about a specific part of the land and record the data to estimate its characteristics and conditions.
LiDAR or laser imaging, detection, and ranging is sometimes referred to as 3-D Laser Scanning and thus can be used to make digital 3-D representations of areas on the earth’s surface and ocean bottom, due to differences in laser return times, and by varying laser wavelengths.
LiDAR was first introduced by Hughes Aircraft Company in the early 1960s where they used Laser scanners in airplanes. But the system didn’t receive its well-deserved fame until the invention of GPS or Global Positioning System in the 1980s.
Before going to the working of LiDAR system, we will talk about different components that make up this system.
LiDAR is generally made up of several components, but the main components include:
Laser Source and Laser Detector: The laser source can be used in generating the energy of the pulses. Since Lasers are classified according to their wavelengths, near-infrared wavelengths are mostly used for terrestrial lidar applications. Generally, the laser used in this system is of low energy and eye-safe. Once, the laser is sent to a specific location, the laser detector or receiver catches or detects the reflected laser pulses coming back from the target object or area in consideration.
Timing Electronics: This component is used to record the data of the timings of a laser pulse in both cases, once the pulse leaves and the return timings of the pulse. Timing Electronics must be able to give precise data to get accurate results. Also, with each pulse sent, there is a possibility of multiple returns since it gets reflected from different parts of the target object. And, thus for precise calculations, each pulse should be timed accurately to get the most accurate measurements.
Global Positioning System (GPS): Global Positioning System or GPS is used to get the precise location of X, Y, Z location of the scanner. To get more accurate results, most lidar systems use a Continuous Operating Reference Station (CORS) or a fixed ground reference station. Thus, to get the most precise results, a comparison of data is done between the collected data from the sensor and the CORS data that has a known location. Data recorded from GPS is processed later and can be used to get accurate positions of the sensor at every second, which in turn can be used to measure sensor position throughout the flight.
Inertia Measurement Unit (IMU): Inertia Measurement Unit (IMU), along with Global Positioning System (GPS) make up the Position and Navigation System that is used to determine the absolute position and orientation of the sensor. IMU works constantly to record the pitch, roll, and yaw of the aircraft. This data is then used to determine the precise angle and location of the lidar system to get an accurate measurement of the distances to surfaces.
Computer System: A well-built computer system is an essential part of a lidar system to ensure that all the individual components of the system are working properly. Data collected from the laser system, GPS and IMU are integrated by the computer system to produce the lidar point data. Most lidar systems consist of an integrated computer system along with software for flight planning, for the integration of IMU/GPS data and for converting sensor data into actual X, Y, Z coordinates.
How do LiDAR works?
LiDAR is also called an active remote sensing system. LiDAR works on the basic principle of collecting data after reflecting a beam of laser light on a specific location and then measuring the timing and orientation of the returned laser to get a precise location of the target object.
In more refined words, LiDAR System records the time taken by the emitted light to travel to the ground and back. That time is then used to measure accurate distance traveled. In turn, the measured distance is then converted to elevation.
These measurements are made using the Position and Navigation System including a GPS that measures the X, Y, Z location of the light energy and an Internal Measurement Unit (IMU) that gives the orientation of the plane in the sky.
Benefits of LiDAR:
- Accuracy: LiDAR technology offers incredibly accurate and most consistent results. The short wavelength used in the system can even detect small objects to create exact 3D models to determine the exact location of the object.
- Speed: Time taken by the sensor to send out laser pulses and receive them back is in nanoseconds.
- Automated Functionality: LiDAR is an automated system making it more efficient.
- Low Cost: LiDAR System is less expensive in comparison to other mapping technologies.
Applications of LIDAR Systems:
- Forestry: Can be used to estimate a variety of forest parameters. Individual trees can be measured and identified easily using lidar data.
- Oceanography: Used for calculating phytoplankton fluorescence and biomass in the ocean surface. It is also used to calculate the depth of the ocean (bathymetry).
- Military: Used in creating a high-resolution map for military purposes.
- Meteorology: Used for studying cloud and its behavior.
- Micro-Topography: Unlike regular Photogrammetry or other survey technology that cannot give the surface elevation value of forest canopy, LiDAR can penetrate through the object and detect the surface value.