How LiDAR sees through the rainforest

20:59>> It It This is This is like as an analogy, this would be like we found Brooklyn and there's 400 things in Brooklyn. And then like New York >> And then Jersey, Connecticut like >> yeah right. And so it's like oh like >> Everything around here is pretty much the same and there's 400 in Brooklyn. So obviously we also have it in Manhattan, the Bronx, etc. >> Yeah. Yeah, it's it's really really cool. So um let's talk about how they actually did it. We always want to focus on the procedure and the methods on this podcast. They use LiDAR. It's effectively using a laser, an infrared laser. What you do is you have a drone or an airplane that has an infrared laser that's sending out laser pulses

21:40hundreds of thousands of laser beams per second downward, okay? >> A laser beam. >> Yeah, it's going to go and scan everything. And then each laser pulse it's going to get split when it hits something. There's going to hit a leaf, part of it's going to go through the leaf, right? And then it's going to hit another leaf. Every time it hits something it bounces back. And [snorts] sometimes it's going to hit the ground and bounce back. >> Have you ever seen these like landscape scanning drones in person before? >> No, I have not. >> It's really creepy. Cuz if you don't know what's happening you kind of kind of just see this like light thing happening and it's just like and it it's clearly programmatic. Yeah, it it's actually quite it's it's interesting.

22:21But I think the point you bring up there is important is we're sending something down, when it hits something comes back. >> Yeah, it's I mean LiDAR sounds like radar because it's the same physics, right? Radar is radio, here we're doing it with light, not necessarily optical light, mostly infrared, right? And then what you do is the computers take all that data and then they remove the top layer of where the leaves are. You can like tell that this bounced back from a leaf, this went all the way down to the ground. You can you can find like a sort of floor of where the bounce happens. >> Because it takes longer. >> Yeah. Yeah, exactly. And you and you just do the timing. >> So you just remove everything that's really short in time. >> Yeah. Yeah, and you look for the extremum in some given like time bin, right? And then once you do that now

23:01you've got a final ground level data, and then you can look for undulations. You can be like there's a earthwork. What that means is there's a mound, and then that mound is going to is going to have a geometric structure, and you can find this out through lidar, >> Right. There's a certain characteristics of like human-made structure >> Yeah. >> that you can basically map to. >> Yeah. >> It's not a hill. >> Mhm. >> Um >> It's got some shape >> Right. >> that's like very weird. >> Circle as an example of a >> Circle, square. >> square that you brought up earlier. >> Exactly. And so the area that they surveyed, um the researchers went