Please correct me if I'm wrong but LiDAR device shoots out multiple laser rays and maps the surroundings based on the time taken by the rays to reflect. But if the LiDAR is placed on a moving vehicle (in case of an Autonomous vehicle), the LiDAR is in linear motion, shooting out the rays continuously.

How do the rays get reflected back to the exact emitter when the whole device is in motion?


LiDAR instrument fires rapid pulses of laser light at a surface and measures the time it takes to return to its source. It does this millions of times a second. Light travels very fast - about 300,000 kilometres per second, 186,000 miles per second or 0.3 metres per nanosecond. Speed of vehicle is only a small fraction of that speed, so you can eliminate it from equation. For this to work, the equipment required to measure this needs to operate extremely fast.

Here is source: http://www.lidar-uk.com/how-lidar-works/

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  • Thanks for the source, that makes sense. Also, I noticed that it emits approximately 150,000 pulses per second and simultaneously detects them. Won't the emitted laser pulses and reflected laser pulses collide and causes inference or dispersion? I am a curious newbie, please bear with me. – user234234234 Jul 3 '19 at 8:43
  • Not sure, but I think the new pulse is emitted only after the previous one is received. The speed of light is so fast that one pulse measure happens practically instantly. Maybe someone with physics background can answer this. – Marin Leontenko Jul 3 '19 at 9:01
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    it depends on the system. on simpler systems the pulse is fired and the systems waits a specific time frame for the echos and detect/samples them. because this limits your range, especially with airborne applications, you can fire the pulse, but detect the echos after the second pulse was fired. this is basically how it is done by all the vendors. more information from optech: lagf.org/2015/pdf/Michael_Sitar.pdf – zwnk Jul 3 '19 at 14:02

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