Green lasers have undeniably elevated the capabilities of LiDAR technology, enabling precise and efficient 3D mapping of our surroundings. Their enhanced visibility, compatibility with silicon-based detectors, and versatility have positioned them as a driving force behind the rapid proliferation of LiDAR across industries. This article presents a concise overview of green lasers in LiDAR, including their functionality, ongoing research, and applications.
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Why are Green Lasers Used in LiDAR?
Light Detection and Ranging (LiDAR) is an advanced remote sensing technique that uses pulsed laser light to measure distances and generate a three-dimensional analysis of the targeted area.
There are two main types of LiDAR: bathymetric and topographic. Topographic LIDAR uses near-infrared lasers to map land features, while bathymetric LIDAR employs green lasers (532 nm wavelength) to measure seafloor and riverbed elevations in water.
The preference for green lasers in bathymetric LiDAR arises from several advantages over traditional red or near-infrared lasers. The key advantage of green lasers is their ability to penetrate water, enabling the measurement of the river, shallow water reservoir, and coastal seawater depths up to three Secchi depths.
Green lasers exhibit strong compatibility with commonly used silicon-based photodetectors due to their wavelength aligning with detector sensitivity. This synergy improves photon capture, enhancing signal quality, signal-to-noise ratio, and efficiency.
The shorter wavelength of green lasers enables energy concentration in each pulse, extending the detection range of LiDAR systems without sacrificing data accuracy. This is particularly advantageous for applications requiring long-range capabilities.
The heightened visibility of green lasers is a standout feature, as human eyes are particularly sensitive to green light. This sensitivity enables better alignment, calibration, and efficiency in underwater LiDAR operations.
How Does the Green Laser Bathymetric LiDAR Work?
In a standard bathymetric LiDAR setup, the scanner emits short-duration green laser pulses (approximately 5-10 ns) at a wavelength of 532 nm towards the target area.
When these pulses hit the target surface, they cause photons to scatter in all directions. A small portion of these scattered photons returns to the LiDAR system, which collects them by a telescope and directs them onto a photodetector.
The time interval between the emission of the green lasers and the detection of the returning signal, known as the time of flight, is measured using onboard sensors. Since the speed of light (c) is a constant, the distance to the target can be determined using the straightforward equation:
Finally, a 3D map of the target area is generated by rapidly scanning the green lasers using rotating mirrors or optical phased arrays and recording return times from various points.
Recent Advancements in Green Lasers for LiDAR Technology
TDOT GREEN: Green Light LiDAR for Aquatic Applications
The Japanese company Amuse Oneself has developed TDOT GREEN, a lightweight green laser LiDAR technology that can be mounted on drones for aerial surveying applications.
TDOT green uses 532nm green lasers at 60,000 pulses per second, allowing underwater mapping down to 5-10 meters. This makes it ideal for extensive surveys of shallow waters, particularly coastal areas.
The technology has been used to map the Dead Sea floor in Israel and Japan's 18,000-mile coastline for climate change monitoring.
Real-Time 3D Mapping through Quantum Detection with Green Lasers in LiDAR
In a study published in Optics Express, researchers from Heriot-Watt University and the University of Edinburgh have used quantum detection via green lasers in LiDAR technology to capture real-time 3D underwater images, even in low-light conditions.
Their technique involved placing a single-photon LiDAR system in a water tank, enabling real-time 3D scene mapping. This innovative approach distinguishes reflected photons from water-scattered ones, making it suitable for turbid waters.
This breakthrough technology holds potential for various applications, including inspecting underwater installations and surveying archaeological sites while contributing to pollution reduction and less intrusive marine monitoring.
Using Green Lasers in Raman LiDAR for Underwater Oil Leak Monitoring
A study published in Applied Optics has proposed an innovative underwater Raman lidar system that employs green lasers to detect and differentiate oil in water.
The team's compact and energy-efficient system can identify the thickness of underwater oil up to 12 meters away, making it highly effective for promptly detecting oil spills. This is achieved through the interaction of green lasers with oil, producing distinctive Raman signals that unequivocally reveal their presence.
The system's success in accurately detecting various oil thicknesses underwater paves the way for applications in monitoring oil pipelines and exploring underwater resources like coral reefs.
Future Outlooks of Green Lasers in LiDAR
Green lasers have significantly improved the potential of LiDAR technology, facilitating accurate and effective three-dimensional mapping of our environment. Their improved visibility, compatibility with silicon detectors, and adaptability have played a pivotal role in the widespread adoption of LiDAR in various sectors.
Researchers are actively investigating hybrid LiDAR systems that merge green and other laser wavelengths to unlock enhanced accuracy, extended range, and advanced capabilities. These innovations are set to drive the evolution of LiDAR technology.
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References and Further Reading
Szafarczyk, A., & Toś, C. (2022). The use of green laser in LiDAR bathymetry: State of the art and recent advancements. Sensors, 23(1), 292. https://doi.org/10.3390/s23010292
Columbia University School of Engineering and Applied Science. (2023). High-performance visible-light lasers that fit on a fingertip. [Online]. ScienceDaily. Available at www.sciencedaily.com/releases/2023/01/230104135615.htm
McNabbon, H. (2022). From the Floor of Intergeo: Amuse Oneself, Green Light LiDAR for Aquatic Applications. [Online]. Available at: https://dronelife.com/2022/10/18/amuse-oneself-green-light-lidar-for-aquatic-applications/?fbclid=IwAR16ZNjhG1iTc700MWfJtPtxcNSV0BqMx5AgmOfKHGKXLQ0gWVF6u3J7TUM
Maccarone, A., Drummond, K., McCarthy, A., Steinlehner, U. K., Tachella, J., Garcia, D. A., ... & Buller, G. S. (2023). Submerged single-photon LiDAR imaging sensor used for real-time 3D scene reconstruction in scattering underwater environments. Optics Express, 31(10), 16690-16708. https://doi.org/10.1364/OE.487129
Shangguan, M., Yang, Z., Shangguan, M., Lin, Z., Liao, Z., Guo, Y., & Liu, C. (2023). Remote sensing oil in water with an all-fiber underwater single-photon Raman lidar. Applied Optics, 62(19), 5301-5305. https://doi.org/10.1364/AO.488872