Car in field of flowers

Lidar system able to penetrate foliage and map obscured environments

Image credit: Dreamstime

A new laser system could improve on current surveying technology by providing a way to detect surroundings beyond partial obscuration, such as netting or vegetation.

Lidar (light and radar) uses the precision of laser to sense an environment. Laser beams are emitted and the amount of time taken for them to be reflected from objects and return to the sensor is measured. This provides the distances from various objects and allows a three-dimensional map of the environment to be built up quickly

It is the standard method for surveying in three dimensions and is now the standard sensory application for self-driving vehicles.

While Lidar is able to see past some obscuration, such as troublesome weather, the system struggles to map an environment obscured by elements such as foliage. When attempting to measure the distance to surfaces behind these obstacles, the original light is mostly blocked, or “thrown away”.

Now, researchers at the Naval Research Laboratory in Washington, DC, have created a new laser system and methodology which could allow Lidar to “see” through minor obstructions for genuine obstacles.

“This was an attempt to address one of the problems with something called foliage-penetrating Lidar,” said Dr Paul Lebow, a research scientist at the Naval Research Laboratory.

“You can actually use it to detect three-dimensional images behind an obscuration such as a tree canopy, for instance, in a disaster-relief situation where you wanted to find people in trouble.”

“You can illuminate using Lidar through the leaves and get enough light coming back through to be able to recreate a three-dimensional, topographic view of what’s going on beneath.”

According to the researchers, their technique has only become viable recently, as before, the “technology wasn’t really there”.

The key to the system is in the interference between two laser beams – travelling in opposite directions – on the sensor. A returning laser beam reaches the sensor and immediately interferes with a newly transmitted beam. The system blocks out the earliest-to-arrive light, which has been reflected from partial obscuration (such as vegetation) and only measures the light returning from the hidden surfaces behind.

“The laser is designed so that the time difference between the local reference pulse and the signal pulse that comes back from the target is completely adjustable to accommodate distances from a few feet to several kilometres,” said Dr Lebow.

The researchers were able to use this new system to see behind mock-foliage in a lab-based demonstration. Now, Dr Lebow and his team hope to continue the project in order to make the foliage-penetrating system field-ready.

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