You know how light reaches the forrest floor? So does LIDAR.
If you get raw data from a LIDAR device (as opposed to the usual commercial internally "processed and smoothed" relatively low frequency data stream) you get a high frequency noisy cloud.
The HF cloud includes returns that bounced from the upper canopy and returns that bounced from the forrest floor.
You write your filters to pick the features (tree tops, tree foor, canopy density estimates, etc) you're interested in.
It's also possible to map recent snowfall depths with LIDAR | microwave RADAR tweaks.
According to [1], they rely on finding holmes in the foliage:
Lidar, of course, does not actually see through vegetation. Rather, it sees through holes in the foliage. Some of the multiple laser pulses it emits simply find openings between leaves and branches, in much the same way that sunlight filters through the forest canopy, continuing down to the ground.
It’s a bit trickier than that; some of the photons from the pulse pass through the canopy to hit the ground. In other words, a single pulse can have multiple detected returns, some from the top of the canopy, some the middle, some the ground.
It’s important to realize that the laser pulse doesn’t remain at the same diameter the whole time; it’s path looks like a cone, albeit a very narrow cone. By the time it hits the ground it can be a couple of metres in diameter.
That two metre wide bunch of photons is what is travelling through the canopy. Some fraction hit the top of the canopy and are reflected; some fraction of the reflected photons travel back in a straight line to the detector, the rest are lost to the environment. The same process repeats until the pulse hits the ground, and whatever photons are left reflect back.
The energy returned to the detector is a tiny fraction of the energy sent out.
Uh, also, that should be "holes", they are not looking for a British fictional detective in the dense foliage of Central America's jungles. Thanks, phone. :|
defrost|3 years ago
You know how light reaches the forrest floor? So does LIDAR.
If you get raw data from a LIDAR device (as opposed to the usual commercial internally "processed and smoothed" relatively low frequency data stream) you get a high frequency noisy cloud.
The HF cloud includes returns that bounced from the upper canopy and returns that bounced from the forrest floor.
You write your filters to pick the features (tree tops, tree foor, canopy density estimates, etc) you're interested in.
It's also possible to map recent snowfall depths with LIDAR | microwave RADAR tweaks.
unwind|3 years ago
According to [1], they rely on finding holmes in the foliage:
Lidar, of course, does not actually see through vegetation. Rather, it sees through holes in the foliage. Some of the multiple laser pulses it emits simply find openings between leaves and branches, in much the same way that sunlight filters through the forest canopy, continuing down to the ground.
[1]: https://www.gislounge.com/next-generation-lidar-seeing-the-f....
geenew|3 years ago
It’s important to realize that the laser pulse doesn’t remain at the same diameter the whole time; it’s path looks like a cone, albeit a very narrow cone. By the time it hits the ground it can be a couple of metres in diameter.
That two metre wide bunch of photons is what is travelling through the canopy. Some fraction hit the top of the canopy and are reflected; some fraction of the reflected photons travel back in a straight line to the detector, the rest are lost to the environment. The same process repeats until the pulse hits the ground, and whatever photons are left reflect back.
The energy returned to the detector is a tiny fraction of the energy sent out.
unwind|3 years ago
unknown|3 years ago
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