New Hyperspectral Raman Imaging Lidar System Detects Plastic

[patricjfrenn]

Researchers have developed an advanced hyperspectral Raman imaging lidar system capable of remotely detecting and identifying various types of plastics. This innovative technology aims to help combat the pressing issue of plastic pollution in the ocean by offering improved tools for monitoring and analysis.

"Plastic pollution represents a significant threat to marine ecosystems and human livelihoods, impacting industries such as fisheries, tourism, and shipping," said Toshihiro Somekawa, leader of the research team at the Institute for Laser Technology in Japan. "To manage and protect the marine environment, it's critical to assess the size, concentration, and distribution of plastic debris, but traditional methods are often slow, labor-intensive, and costly."

Described in Optics Letters, a journal of the Optica Publishing Group, the new system is compact and energy-efficient, making it ideal for use on drones. The system can identify plastics from a distance of 6 meters with a broad field of view of 1 mm by 150 mm.

"A drone equipped with our lidar sensor could be used to assess marine plastic debris both on land and at sea, enabling more targeted cleanup and prevention efforts," Somekawa explained. "This technology could also be applied to other monitoring tasks, such as detecting hazardous gas leaks."

The researchers previously demonstrated a flash Raman lidar technique for monitoring systems, where bandpass filters were applied to each target measurement. However, this method was not practical for detecting marine plastics because switching filters would interfere with real-time 3D detection.

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While other groups have used hyperspectral Raman imaging to monitor plastic pollution, this technique typically works only over short distances. To address this limitation, the researchers combined lidar for distance measurement with hyperspectral Raman spectroscopy. They created a prototype system that includes a pulsed 532-nm green laser for lidar measurements and a 2D imaging spectrometer with a gated intensified CCD (ICCD). The backscattered Raman signal from distant targets was detected as a vertical line, and the hyperspectral information was recorded horizontally.

"Our system is designed to capture both images and spectroscopic data simultaneously," said Somekawa. "Since each plastic type has a unique Raman spectrum, the imaging data provides insight into the spatial distribution and type of plastic debris, while the hyperspectral information can be obtained from targets at any distance thanks to the pulsed laser enabling precise range-resolved measurements."

The team tested their system on a plastic sample consisting of a polyethylene sheet on top and a polypropylene sheet below. From 6 meters away, the system successfully identified the characteristic spectra of each plastic and produced images showing their vertical distribution. The system's imaging pixel size of 0.29 millimeters at this distance suggests it can also measure and analyze small plastic debris.

Next, the researchers plan to use their system to monitor microplastics in both floating and submerged forms. Given that laser light at 532 nm passes effectively through water, this will enhance detection capabilities in aquatic environments.