Compact Single-Photon Lidar Provides High Resolution for Air and Space

Despite advancements in airborne, single-photon lidar, existing systems have relatively large payloads and high energy consumption.

Researchers at the University of Science and Technology of China (USTC) addressed these challenges and achieved a compact, lightweight, single-photon lidar system with a low-power payload and high-resolution imaging. The new system could make lidar practical for air and space applications like environmental monitoring, 3D terrain mapping, and object identification.

To reduce the system size, the researchers used small telescopes with an optical aperture of 47 mm as the receiving optics. Despite the limited aperture, the team was able to enhance the image resolution by using scanning mirrors to perform sub-pixel fine scanning.

A new compact and lightweight single-photon airborne lidar system could make single-photon lidar practical for air and space applications such as 3D terrain mapping. Courtesy of Feihu Xu, University of Science and Technology of China.

The researchers also needed to limit the lidar’s laser power — a step that could weaken the echo signal from the ground target, making it difficult to reconstruct high-quality images. Using photon-efficient computational algorithms and high-performance single-photon avalanche diode (SPAD) arrays, the researchers achieved a low laser power of 150 mW. This approach allowed the researchers to reconstruct high-quality images regardless of a weak echo signal.

“A key part of the new system is the special scanning mirrors that perform continuous fine scanning, capturing sub-pixel information of the ground targets,” professor Feihu Xu said. “Also, a new photon-efficient computational algorithm extracts this sub-pixel information from a small number of raw photon detections, enabling the reconstruction of superresolution 3D images despite the challenges posed by weak signals and strong solar noise.”

A pre-flight ground test confirmed that the system could perform lidar imaging with a resolution of 15 cm from 1.5 km away with default settings. Once the researchers implemented sub-pixel scanning and the 3D deconvolution algorithm, the system demonstrated an effective resolution of 6 cm from the same distance. In an airborne experiment, the system realized high-resolution imaging superior to 40 cm, with an optical aperture of only 47 mm.

Single-photon lidar is particularly useful for airborne applications because it enables highly accurate 3D mapping of terrain and objects even in urban areas and environments with dense vegetation. Measuring the time-of-flight of the returned single photons makes it possible to calculate the time it takes for the light to travel to the ground and back. The detailed 3D images of the terrain can be reconstructed from this information using computational imaging algorithms.

The team conducted experiments aboard a small plane over a period of several weeks to show that the system could capture high-resolution 3D images over large areas during the daytime. The experiments revealed detailed features of various landforms and objects, demonstrating the functionality and reliability of the system in real-world scenarios and its potential for remote sensing.

The system demonstrated the ability to reconstruct images from noisy data, even under demanding conditions and with limited laser power. The system’s photon-efficient capabilities enabled the researchers to reconstruct high-quality images with two signal photons per pixel, to use for the clear identification of ground targets.

Results from airborne test are shown. The researchers demonstrated the system’s real-world ability by using it aboard a small plane to capture high-resolution 3D images during daytime over large areas. Courtesy of Feihu Xu, University of Science and Technology of China.

The work of the USTC team shows that a single-photon airborne lidar system can overcome constraints on laser power and optical aperture through photon efficiency and techniques to achieve superresolution.

“Using single-photon lidar technology on resource-limited drones or satellites requires shrinking the entire system and reducing its energy consumption,” Xu said. “We were able to incorporate recent technology developments into a system that, in comparison to other state-of-the-art airborne lidar systems, employs the lowest laser power and the smallest optical aperture while still maintaining good performance in terms of detection range and imaging resolution.”

The technology developed by USTC could contribute to the development of future low-power, compact, airborne and spaceborne, single-photon lidar systems with high-altitude, large-scale, high-resolution imaging capabilities.

“Ultimately, our work has the potential to enhance our understanding of the world around us and contribute to a more sustainable and informed future for all,” Xu said. “For example, our system could be deployed on drones or small satellites to monitor changes in forest landscapes, such as deforestation or other impacts on forest health. It could also be used after earthquakes to generate 3D terrain maps that could help assess the extent of damage and guide rescue teams, potentially saving lives.”

The team is currently working to enhance the performance and integration of the system, with a long-term goal of installing it on a spaceborne platform such as a small satellite. Improvements in the stability, durability, and cost-effectiveness of the system will be needed before it can be commercialized.

The research was published in Optica (www.doi.org/10.1364/OPTICA.518999).