3 ms·

How do the LIDARs work for this kind of thing? I always imagined that the light used wouldn't be able to penetrate objects that are opaque in the visible light

How do the LIDARs work for this kind of thing? I always imagined that the light used wouldn't be able to penetrate objects that are opaque in the visible light spectrum.

defrost 2y ago
If sunlight can reach the forest floor then so can LIDAR. An airframe with a LIDAR device scatter shots a medium angle "spotlight" of pulses at high frequency downwards within an arc area of angles (straight down, a bit to the left, a bit to the right, a bit forward, etc.) Of the tens of thousands of 'RAW' data points many reflect from top canopy leaf cover, many penetrate further, a lesser number reach the ground. All the raw points are pipeline processed and the floor() of penetration is extracted from the fuzzy cloud that represents the canopy as a whole. Ancient banks, levels, roads, et al show up where not eroded as per the image in the article.
- naikrovek 2y ago
  Why do tree trunks not show up?
  - defrost 2y ago
    Standing or fallen? .. and who says that fallen logs don't show up? Bear in mind that the final display is a processed data product with any number of artefacts smoothed, filtered, or cut away by a data processor.
- roughly 2y ago
  Even when eroded, the presence of straight lines in the eroded remains has typically been used to identify human-made structures.
sampo 2y ago
Here is a fisheye photo from the bottom of a rainforest. As you can see, some spots of sky are visible from the bottom. When you fly above the forest and LIDAR is looking down, similarly at some spots the LIDAR laser beams are able to hit all the way to the bottom at some spots through the canopy. It's not a big fraction, but some of the laser beams are hitting the ground, and after data processing you filter them out and they five you the ground topography profile. https://www.sciencephoto.com/media/972412/view/rainforest-canopy-viewed-though-circular-fisheye-lens https://www.sciencephoto.com/media/972412/view/rainforest-ca... Here is a side view that shows how the point cloud profile can look like. This is not from a rainforest but some other forest. https://www.researchgate.net/figure/LiDAR-point-cloud-profile-in-which-a-is-the-3D-point-cloud-in-the-research-area-and_fig3_372932889 https://www.researchgate.net/figure/LiDAR-point-cloud-profil...

How do the LIDARs work for this kind of thing? I always imagined that the light used wouldn't be able to penetrate objects that are opaque in the visible light spectrum.

defrost 2y ago

If sunlight can reach the forest floor then so can LIDAR. An airframe with a LIDAR device scatter shots a medium angle "spotlight" of pulses at high frequency downwards within an arc area of angles (straight down, a bit to the left, a bit to the right, a bit forward, etc.) Of the tens of thousands of 'RAW' data points many reflect from top canopy leaf cover, many penetrate further, a lesser number reach the ground. All the raw points are pipeline processed and the floor() of penetration is extracted from the fuzzy cloud that represents the canopy as a whole. Ancient banks, levels, roads, et al show up where not eroded as per the image in the article.

naikrovek 2y ago
Why do tree trunks not show up?
- defrost 2y ago
  Standing or fallen? .. and who says that fallen logs don't show up? Bear in mind that the final display is a processed data product with any number of artefacts smoothed, filtered, or cut away by a data processor.
roughly 2y ago
Even when eroded, the presence of straight lines in the eroded remains has typically been used to identify human-made structures.

sampo 2y ago

Here is a fisheye photo from the bottom of a rainforest. As you can see, some spots of sky are visible from the bottom. When you fly above the forest and LIDAR is looking down, similarly at some spots the LIDAR laser beams are able to hit all the way to the bottom at some spots through the canopy. It's not a big fraction, but some of the laser beams are hitting the ground, and after data processing you filter them out and they five you the ground topography profile. https://www.sciencephoto.com/media/972412/view/rainforest-canopy-viewed-though-circular-fisheye-lens https://www.sciencephoto.com/media/972412/view/rainforest-ca... Here is a side view that shows how the point cloud profile can look like. This is not from a rainforest but some other forest. https://www.researchgate.net/figure/LiDAR-point-cloud-profile-in-which-a-is-the-3D-point-cloud-in-the-research-area-and_fig3_372932889 https://www.researchgate.net/figure/LiDAR-point-cloud-profil...