LIDAR
LiDAR or Light Detection and Ranging is an active remote sensing system which has recently taken a stark increase in its usage in many areas . It is majorly used for remote sensing application to study the geography of an area because indubitably it is impossible to go and measure the height of the tree’s in the region . Thus using certain advanced sensors to get the topography of region is of the prime importance for various research and study .
LIDAR has been used for a number of applications such as:
- 1990s: LIDAR is widely used for geographical mapping.
- 1994: NASA takes LIDAR into space on the Space Shuttle Discovery. LITE (Lidar In-Space Technology Experiment) is the first time LIDAR had been used to study the atmosphere from space.
- 2005: LIDAR systems make the headlines as the eyes behind self-driving cars in the US military’s DARPA Grand Challenge.
- 2008: NASA’s Phoenix Lander takes an Optech LIDAR scanner to Mars to study the planet’s atmosphere.
- 2015: DARPA announces that it has created Sweeper, a miniature LIDAR system on a single chip (“Sweeper” stands for Short-range Wide-field-of-view Extremely agile Electronically steered Photonic EmitteR).
- 2017: The Environment Agency of England and Wales announces it will LIDAR scan the whole of England and make the data publicly available.
- 2020: Apple includes LIDAR in its latest iPad to improve 3D modeling of the environment around it for augmented reality applications. Before self driving cars and augmented reality came into picture the geographers mainly used it to draw detailed map of the surface of the earth for research purposes .
SO HOW DOES IT WORK?
LIDAR fires invisible laser beams in all directions, catching the reflections, and measuring how long the beams take to return so it can figure out what obstacles are nearby and how far away they are. So the basic concept of LIDAR is exactly the same as radar and sonar. With RADAR, you might have a jet plane firing out a beam of coded radio waves and listening for a return beam reflected off some nearby object (maybe another plane about to crash into you ☺☺ ); it uses the time taken for the beam to return to figure out how far away the object is. With SONAR, you do the same thing underwater, only using sound waves (because ordinary light and radio waves don’t travel through water very far). In everyday, on-land situations — driving down the street or navigating through a building — reflected laser light turns out to be a better source of information than either radio waves or sound, and that’s why LIDAR has become so popular: it’s simple, reliable, and relatively low-cost, if still very expensive for amateur or hobbyist use (currently, we’re talking thousands of dollars).
How Does LIDAR Work?
The working principle of Light Detection and Ranging system is really quite simple. A LIDAR sensor mounted on an aircraft or helicopter. It generates Laser pulse train, which sent to the surface/target to measure the time and it takes to return to its source. The actual calculation for measuring how far a returning light photon has traveled to and from an object is calculated by Distance = (Speed of Light x Time of Flight) / 2
The laser instrument fires rapid pulses of laser light at a surface, some at up to 150,000 pulses per second. A sensor on the instrument measures the amount of time takes for each pulse to reflect back. Light moves at a constant and known speed so the LIDAR instrument can calculate the distance between itself and the target with high accuracy. By repeating this in quick progression the instrument builds up a complex ‘map’ of the surface it is measuring.
With airborne Light Detection and Ranging, other data must be collected to ensure accuracy. As the sensor is moving height, location and orientation of the instrument must be included to determine the position of the laser pulse at the time of sending and the time of return. This extra information is crucial to the data’s integrity. With ground-based Light Detection and Ranging a single GPS location can be added at each location where the instrument is set up.
