5 ms·

How does lidar see through a hedge?

xnzakg 10y ago
Probably was a radar, not a lidar.
mseebach 10y ago
Possibly infrared sensing? Some fancy IR cameras can see a human body through walls, so I guess it's not inconceivable that a LIDAR (which is already IR, I think?) could penetrate a hedge.
- swiley 10y ago
  You're thinking of far IR (typical black body radiation at room temperature for most materials) near IR is what has to be filtered out in web cams and what a lot of these LIDAR devices use, it behaves almost exactly like visible light.
willvarfar 10y ago
LIDAR can practically see through vegetation. Some individual beams miss the vegetation and reflect from things they hit on the far side, and the software can detect this. This is used a lot in mapping and research into e.g. forest canopies in the amazon. LIDAR has been extensively deployed on aircraft for this kind of purpose. I've seen high-res LIDAR scans made available by my country's state survey for e.g. archeologists and it has the 'true ground' through the vegetation. Its like the vegetation has been stripped away and has a clinical feel when rendered.
- mturmon 10y ago
  This is a good summary. Some lidars also offer two distance estimates per point, a first distance and a secondary distance. On the lidar I used that had this capability, the secondary distance was not always robust. But on permeable materials like vegetation, the secondary distance would typically indicate solid materials behind the initial curtain of material. Anyway, the presence of multiple distance returns in a small solid-angle area (whether from the above primary/secondary, or from nearby scan points) can indicate density of vegetation. You can certainly see "through" the small gaps in a hedge. Depending on the lidar, and the range, gaps as small as a few cm^2 could be enough (talking about vehicle-mounded lidar for autonomous navigation, not remote sensing of forest canopy).

Probably was a radar, not a lidar.

Possibly infrared sensing? Some fancy IR cameras can see a human body through walls, so I guess it's not inconceivable that a LIDAR (which is already IR, I think?) could penetrate a hedge.

swiley 10y ago
You're thinking of far IR (typical black body radiation at room temperature for most materials) near IR is what has to be filtered out in web cams and what a lot of these LIDAR devices use, it behaves almost exactly like visible light.

willvarfar 10y ago

LIDAR can practically see through vegetation. Some individual beams miss the vegetation and reflect from things they hit on the far side, and the software can detect this. This is used a lot in mapping and research into e.g. forest canopies in the amazon. LIDAR has been extensively deployed on aircraft for this kind of purpose. I've seen high-res LIDAR scans made available by my country's state survey for e.g. archeologists and it has the 'true ground' through the vegetation. Its like the vegetation has been stripped away and has a clinical feel when rendered.

mturmon 10y ago
This is a good summary. Some lidars also offer two distance estimates per point, a first distance and a secondary distance. On the lidar I used that had this capability, the secondary distance was not always robust. But on permeable materials like vegetation, the secondary distance would typically indicate solid materials behind the initial curtain of material. Anyway, the presence of multiple distance returns in a small solid-angle area (whether from the above primary/secondary, or from nearby scan points) can indicate density of vegetation. You can certainly see "through" the small gaps in a hedge. Depending on the lidar, and the range, gaps as small as a few cm^2 could be enough (talking about vehicle-mounded lidar for autonomous navigation, not remote sensing of forest canopy).