[Chode]

i fail to see how it goes through the trees/leaves

[sparklite2]

i fail to see how it goes through the trees/leaves

---

First, it eats the roots and shoots.

[mairdie]

Still doesn’t say what happens when the leaf canopy is solid.

https://www.osa.org/en-us/about_osa/newsroom/news_releases/2017/seeing_the_forest_through_the_trees_with_a_new_lid/

Seeing the Forest Through the Trees with a New LiDAR System

“The real key to making our system work is the interference between two laser beams on the sensor. We send one laser beam out to the target and then it returns, and at the exact same time that return [beam] hits the detector, we interfere it locally with another laser beam,” Watnik said. “We need complete coherence between those beams such that they interfere with one another, so we had to have a specially designed laser system to ensure that we would get that coherence when they interfere on the camera.”

Using a pulsed laser with pulse widths of several nanoseconds, and gated measurements with similar time resolution, the holographic system selectively blocks the earliest-to-arrive light reflecting off obscurations. The camera then only measures light coming back from the partially hidden surface below.

https://oceanservice.noaa.gov/facts/lidar.html

How is LIDAR data collected?

When an airborne laser is pointed at a targeted area on the ground, the beam of light is reflected by the surface it encounters. A sensor records this reflected light to measure a range. When laser ranges are combined with position and orientation data generated from integrated GPS and Inertial Measurement Unit systems, scan angles, and calibration data, the result is a dense, detail-rich group of elevation points, called a “point cloud.”

Each point in the point cloud has three-dimensional spatial coordinates (latitude, longitude, and height) that correspond to a particular point on the Earth’s surface from which a laser pulse was reflected. The point clouds are used to generate other geospatial products, such as digital elevation models, canopy models, building models, and contours.

[Lurker]

It eats, shoots, and leaves.

L

[TXnMA]

"i fail to see how it goes through the trees/leaves"

If you bombard a forest with a dense-enough "cloud" of laser pulses, statistically, some of them will "find holes between the leaves" and reach the ground -- and will be the last to be reflected back to the detector. By subtracting out all the "quick returns", all you have left is those that reflected back from the "bare ground".

Ideally, in a temperate area, you do the overflight in winter, when foliage is at a minimum...

But, I agree with you: getting enough pulses through a triple-canopy jungle must be a genuine challenge!