Dr. Fanghua Liu Profile

Dr. Fanghua Liu

at Shanghai Institute of Optics

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Publications (2)

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Proceedings Article | 1 November 2021 Paper

Airborne Geiger-mode lidar system with real-time data compression

Fanghua Liu, Yan He, Luo Yuan, Yongqiang Chen, Congmiao Jiao, Jiayong Yu, Shouchuan Guo, Yifan Huang, Weibiao Chen

Proceedings Volume 12057, 120573U (2021) https://doi.org/10.1117/12.2606698

KEYWORDS: LIDAR, Data compression, Clouds, Data storage, Image compression, Field programmable gate arrays, Data transmission, Algorithms, Airborne remote sensing

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Due to the high detection sensitivity and efficiency, single photon time-of-flight distance ranging Lidar have emerged in rapid, large scale, high resolution, topographic mapping in recent years. We designed an airborne mapping Lidar system based on arrays of Geiger-mode Avalanche Photodiode (GmAPD) detectors capable of detecting a single photon, and the area coverage rates in excess of 122 km2 /hr. The Lidar system uses an eye-safe, low-power fiber laser and a 64×64 pixel GmAPD arrays capable of readout rates in excess of 20 KHz. Although large-pixel-format GmAPD detector array can obtain plenty laser point cloud in one frame, but the requirement of raw data transmission and storage rate would be particular high when the detect repetition frequency reach at 20 KHz or even more. Therefore, we proposed a lossy realtime data compression algorithm which can reduce a half of data transmission and storage rate so that the data can transmission through low bandwidth situation. By analysis the quality of point cloud, this lossy real-time data compression method had been validated works well during our airborne experiment which had carried out in Wuhu city, China. For a single mapping strip, the point cloud had a mean measurement density greater than 110 points per square meter in flat topography and 75 points per square meter in rough topography when the aircraft above ground levels (AGLs) was 1 km and velocity was 220 km/h.

Proceedings Article | 20 November 2019 Paper

Miniaturized underwater polarized radiation measuring instrument

Kaipeng Li, Yan He, Peng Chen, Yufei Zhang, Fanghua Liu, Xiaolei Zhu, Weibiao Chen

Proceedings Volume 11191, 1119115 (2019) https://doi.org/10.1117/12.2538741

KEYWORDS: Telecommunications, Polarization, Particles, Computing systems, LIDAR, Pulsed laser operation, Photomultipliers, Control systems, Iris recognition, Ocean optics

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A miniaturized underwater polarized radiation measuring instrument (MUPRMI) LiDAR system applied in detecting the polarization optical parameter profiles for shallow water has been designed. This system will be used for detecting the depolarization of laser propagating underwater. For that purpose, a 532 nm linearly polarized laser with the repetition rate of 100 Hz and per pulse of energy of 50 μJ will be used in the system. When propagating underwater, the polarization state of laser will be changed in case of collision with the particles suspended in water. The linearly polarized laser will gradually become non-polarized due to depolarization, and the depolarization degree is related to the suspended particles. In order to detect the depolarization effect of waters, two orthogonal polarization receiving channels have been assembled in the MUPRMI system. For signal receiving, a photomultiplier tube has been assembled in each of the channels. By detecting the change of polarization state, parameters of scattering particles suspended in water in the detecting area can be inverted using inversion algorithm. The MUPRMI system can be controlled by a host computer, which communicate with the MUPRMI system using ethernet communication protocol. An adjustable aperture driven by a stepping motor has been assembled in the receiving optical path. Using this adjustable diaphragm, we can control the change of receiving field of view by transmitting instructions from the host computer, and change the reception of signals from different kind waters. A ship-borne experiments have been conducted in South China Sea, results show that the deepest bathymetry of the MUPRMI system is about 9 meters with the pulse energy of 50 μJ, in South China Sea.

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