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How Does LiDAR Remote Sensing Work? Light Detection and Ranging


So LiDAR or light detection and
ranging uses lasers to measure the elevation of things like the ground forests and even buildings. It’s a lot like sonar which uses sound waves to map things, or radar which uses radio waves to map things, but a LiDAR system uses light sent out
from a laser. But aren’t lasers used for stuff like, I don’t know, scanning barcodes, making your favorite band look awesome, removing hair? Eww! Seriously how does a LiDAR system use lasers to measure stuff? Now just for the record there are
different ways to collect LiDAR data from the ground, from an airplane, or even from space. Airborne LiDAR data are the most commonly available LiDAR data and airborne LiDAR data will also be freely available through the National Ecological Observatory Network or NEON. So we’ll focus on that in this video. So to get how lasers are used to calculate height in airborne LiDAR, we need to understand the four parts in the system. First, the airplane contains the LiDAR
unit itself which uses a laser to scan the earth
from side to side as the plane flies. By the way, for your remote sensing geeks out there, the laser system uses either green or
near infrared light because these wavelengths or types of light reflect strongly off of vegetation. The next component of a LiDAR system is
a GPS receiver that tracks the altitude and XY location of
the airplane The GPS allows us to figure out where LiDAR reflections are on the ground. The third component of the LiDAR system is what’s called an inertial measurement unit or IMU not to be confused emu — an IMU. The IMU tracks the tilt of the plane in the sky as it flies. which is important for accurate elevation calculations. Finally, the LiDAR system includes a computer. The computer records all that important height information that the LiDAR collects as it scans the earth’s surface. No computer, no data. It’s as simple as that. Now you may be wondering how the laser, the GPS, the IMU and the computer all work together to get us these fantastically useful later dataset? Well, the laser in the LiDAR system scans
the earth actively emitting light energy towards
the ground. Now before we go any farther, let us get two key LiDAR terms associated with this emitted light energy out of the way. You know, so we can speak LiDAR and all. First, let’s define the word “pulse”. A pulse simply refers to a burst of light
energy that is admitted by the LiDAR system. And second, lets define the word “return”. Return the first reflected light energy
that has been recorded by the LiDAR sensor. So pulses of light energy travel to the
ground and return back to the LiDAR sensor. Now we’re speaking LiDAR. Now all of this pulse and return business is great but speaking a language doesn’t give us height. To get height the LiDAR system records the time that it takes for the light energy to travel to the ground and back. The system then uses the speed of lightto calculate the distance between the top but that object and the plane. So let’s break down with this distance calculation looks like: you take travel time multiplied by the speed of light, divided by 2 since the light traveled to
the ground and back. This calculation gives us how far the
light actually traveled to the ground. So using this math, we know the distance between the plane in the ground. But we’re not done just yet. How do we figure out the actual elevation of the ground? To figure ground elevation, we take the plane’s altitude, calculated using that GPS receiver and then we subtract the distance that the light travel to the ground. And that covers the basics of how a LiDAR system uses lasers to measure height. So now we’ve got the basics down. But there are two more things in a
LiDAR system has to consider when calculating height. First, the plane rocks a bit in the sky as it flies due to turbulence in the air. These movements are recorded by the
inertial measurement unit or IMU. No, no, no, not emu. IMU. So that they can be accounted for when
height values are calculated for each LiDAR return. and also an airborne system scans the earth from side to side to cover a larger area on the ground when flying. So while some light pulses travel vertically from the plane to the ground or directly at nadir, if we’re still talking LiDAR lingo here, most pulses leave the plane angle or off nadir. so the system also needs to account for pulse angle when it calculates elevation. So let’s put this all together one last time the LiDAR system emits pulses of light energy towards the ground using a laser it then records the time it takes for the
pulse to travel to the ground and return back to the sensor. It converts this time to distance using
the speed of light. The system then uses the plane’s
altitude, tilt, and the angle of the pulse to
calculate elevation. It also uses a GPS receiver calculate
the object’s location on the ground. All this information is recorded on that
handy dandy computer also mounted on the airplane. And that, my friends, is how a LiDAR system works. Now, there is one component of a LiDAR
system that makes it so useful. A pulse light doesn’t just reflect off one thing like the top of a tree and yield one return. Sometimes a LiDAR pulse travels through things like the gaps between tree branches and leaves. Think about standing on the forest floor and watching the sunlight filter through the top to the trees making the leaves and branches glow. So light energy that passes through
the canopy reflects of the branches and leaves within the canopy. This ability of a LiDAR system to
travel through and record information starting from the
top of the canopy, through the canopy, and all the way to the
ground makes LiDAR systems unique and highly
valuable to scientists studying trees. These returns from within the canopy
tell us more about what’s happening inside the forest, or the forest structure. For example, they can tell us about the shape of the trees or the density of the leaves on the trees. They can sometimes even be used to
estimate whether they’re shrubs below the trees on the forest floor but we’ll save that topic of using LiDAR to estimate forest structure for another video. And, now my friends, you know how a LiDAR system generally works and also, you can consider yourself fluent in the language of LiDAR. (music)

Glenn Chapman

100 Comments

  1. Lolo! Very entertaining and informative video on LiDAR! Always wondered what the heck it was and this video did the job great and with jokes! May take a remote sensing class now :O

  2. Is LIDAR's laser harmful to eyes of humans or animals?Thanks in advance.

  3. Excellent video. Explained it really well. I'll use what I've learnt here for my upcoming exam.

  4. Seems wrong. As the laser leaves the airplane, the airplane moves forward, thus when the laser “returns” back to the airplane, the airplane has moved. And you have to take into account that if you send several photons at the same time, given the fact the airplane has a velocity, you have a bit more math to do to know which laser was what when it left the airplane.

  5. Ancient greeks invented lasers etc and barbarians stole it, the ancient bluprints. Now they make patents and telling greeks do not copy us. Lol. How about aliens gonna kick your ass for stealing greek technology and killing greeks? Soon

  6. enough to make you think something is harder to do than it actually is..

  7. A few details: adding sound effects every time you change the picture is annoying. Your diagram showing circles passing through the satellite and the airplane is pretty meaningless. Circles centered on each satellite, or straight lines between satellite and airplane, maybe.

  8. I had a question, so LIDAR sensors can register only one point on ground surface at one time? If not how does the LIDAR sensor differentiate between multiple reflected pulses at one instance of time?

  9. It is really amazing i like it very much i have been looking for such technology that makes life easy and cost effective for my research work and my life as well.

  10. This is great! I've been doing research in LiDAR for a while and i'll probably point people to this video when they want to know what the hell I do ahah!!

  11. It's very cool tech, but I've got feeling that computer gotta be very fast in order to get such amount of incoming data from laser…

  12. This is a great video. I have watched it many times over the last 8 months for college and each time I pick up some little detail I didn't remember from the last time I watched it. Very good Video. Thank you. Thank you also for going into the pulse return a little deeper in the comments section, I too was wondering about that as well. Thank you again.

  13. Really great video. It is videos like this that made me make my own videos on prospecting and geology (frank reiser m.s.). When are we going to see more videos?
    Sincerely,
    Frank
    Frank's Beautiful Rocks and Minerals

  14. This was a great educational video that our company will use to help educate our future employees for further growth and development, keep up the great work, you guys just got a subscriber!!!!!!!!!!!!!!!!!!

  15. What is the resolution of LIDAR. Would this be good technology to map a boulder train that extends over 20 miles and is between 100 and 300 yards wide. How expensive is it to have done? Are there companies that provide this service for private parties? TY

  16. If I'm understanding correctly…. LIDAR is strictly a distance measuring tool. For example, LIDAR is a collision avoidance device. Self-driving cars use ANOTHER technology to read stop signs and lane division markings. Right?

  17. Firstly thank you for this useful info.
    can LiDAR detect fire flame? need your advice. Thank you

  18. scientists also use this technology as a numbing agent. they call it Lidarcane. >_>

    I'll see myself out.

  19. Can't watch this.  Irritating voice and kowtowing to younger audience make me sick.  I will find some other one.

  20. I leave the video narrating in the background while I browse in another tab, and emus start screaming at me.

  21. Very informative, thank you for taking the time to make this video!

  22. Great and helpful video. The emu joke was cringe, but actually extremely useful, as I will remember IMU for my exam tomorrow! Thanks 🙂

  23. Well, I feel smarter now. This was very helpful and you made it fun.

  24. Nicely explained the working method of LiDAR. Good for initial knowledge. Thanks.

  25. Nice video. I have one doubt, if the laser light is sent to a flat ground from certain height at an angle say theta from normal to the ground how come the receivers receive the ray back? Shouldn't it travel with theta angle normal to the ground in other direction?

  26. It took way too long to get to the details. You didn't need to define pulse and return.

  27. Exellent presentation,
    Bravo,
    we need more video to share to help students
    Thanks

  28. As a geoscientist working a lot with ALS I commend this video so much. Most of our highly demanding clients that have stolen our specs have no idea. And yes, I had a client asking why do we joke so much about Emu's. Yes, we are in Australia!

  29. why do we use lidar in autonomous vehicles like one by google, when we can afford the system using radar which is more cheap

  30. But how to translate this to computer language, meaning "simulation" any thoughts ?

  31. when people ask why UFOs have lights, i believe its probably their version of LIDAR

  32. Thank you! Very well done! Great Narrative! Great visuals! 🤓 I just learned a lot!

  33. hello everyone , i have las file me required production data for transmission line can help me

  34. I have a (maybe-stupid) question: how does the sensor detect the pulse that was sent not perpendicularly to the ground?
    It should be reflected away from the airplane, right?

  35. Wow nice video! Graphics are pretty good. Thanks for sharing LiDAR information through a very nice video. https://www.modusrobotics.com/

  36. Great. also share you a good 40m RS232 laser distance sensor 701A: https://www.youtube.com/watch?v=4PRwGOyittk

  37. hmmm last time i checked radio waves are light, so the difference is that lidar uses a different type of light

  38. I wish i could reach my dreams school at Remote Sensing Chiba University Japan. Thanks for knowledge and sharing this video

  39. These lidar systems do not use TOF. They use a linear ccd system. It looks where the laser Shines on an object. There is a distance between the laser emitter and the ccd. The laser is angled towards the CCD where it sees the laser. It can calculate the distance to its point of reference.

  40. These and other instructional/educational videos are crucial. We need more of this on the internet. I work in the GEOINT field and find this to be the most comprehensive instructional piece to explain LiDAR to my subordinates and leadership.

  41. Yes ,all that is good for the killing of nature and change the clime.

  42. Cant you just make it receives Sun light and calculate where it comes from?

  43. an excellent way to explain using humor, BRAVO

  44. Lidar is nowadays a common noun that people do not bother capitalizing it, similar to Laser, Maser, Radar, and Sonar which were originally acronyms for "Light Amplification by Stimulated Emission of Radiation", "Microwave Amplification by Stimulated Emission of Radiation", "Radio Detection And Ranging" or "Radio Direction And Ranging", and "SOund Navigation And Ranging".

  45. nice video. can anyone tell me what the grund elevation is and why we take the 2024m (Why??) – distance (1000??? WHY where do i get this from) (at: 3:54.) Why do we do this calculation?

    Thanks a lot.!!

  46. Awesome animations! Well explained! This video accomplishes the complex task of connecting with the masses. Lol

  47. the person viewing this topic and video knows the difference between IMU and imu…

  48. the most interesting thing – how time of 1/300000000 second (which light spend to travel 1 meter) is measured – is not covered in this video.

  49. What if it gets multiple returns from one transmission? Is this possible

  50. Hello, how interesting video it is! I really want to know how to estimate forest structure but i can't find it out in your videos. Have you been posted or not yet? Please…… I'm very interested in the next steps. Many thanks.

  51. Question? Why cant lidar be used on a satalight and used on mars to ses if any cultures have been there already .it would finally prove it .or not. I would love to be part of it if ever was done

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