In one line
LiDAR (Light Detection and Ranging) fires short laser pulses at objects and measures how long the reflected light takes to return, converting that time into distance.
Explained simply
It is like shouting in a valley and timing the echo, except it uses light pulses instead of sound. Since light travels at a known speed, the return time tells exactly how far away the object is. By scanning millions of pulses in all directions, LiDAR builds a 3D "point cloud" of the surroundings.
How it works
- A pulsed laser (often near-infrared, such as 905 nm or 1550 nm) emits a very short pulse.
- A scanner (rotating mirror or electronic steering) points the pulse in a known direction.
- The pulse hits an object and part of it scatters back.
- A sensitive photodetector receives the returning pulse, and a timer measures the round-trip time \(t\).
- Distance \(d = ct/2\) is calculated; with direction angles and GPS/IMU position data, each return gives a 3D point.
- Repeating this very rapidly gives a 3D map of the scene.
Laser is used because its beam is highly directional (small spot, fine detail), intense (strong return) and monochromatic (filters can block sunlight).
Key formula
\(d = \dfrac{c\,t}{2}\), where \(d\) is the distance to the object (m), \(c = 3\times10^8\) m/s and \(t\) is the round-trip time (s). The factor 2 is because light travels there and back.
Quick example
A pulse returns after \(t = 2\) μs. Then \(d = (3\times10^8 \times 2\times10^{-6})/2 = 300\) m. Uses: self-driving cars detecting pedestrians, terrain and forest mapping from aircraft, flood and coastline surveys, and wind and pollution studies in the atmosphere.
Common mistakes
- Forgetting the factor of 2 in \(d = ct/2\).
- Confusing LiDAR with RADAR; RADAR uses radio waves, LiDAR uses light.
- Thinking LiDAR uses continuous light only; most systems use short pulses.
How MU asks it
The syllabus asks for elementary knowledge, so expect "Write a short note on LiDAR" (3 to 5 marks). Write the full form, principle (time of flight), a block diagram (laser, scanner, target, detector, timer, processor), the formula and three applications.