Airborne Polarization Lidar With 1.5?m Single-Photon Detectors

Since the invention of polarization lidar in 1971,it has been playing an important role in atmospheric detection.Since polarization lidars need two channels detection,it requires higher system stability than ordinary atmospheric detection lidar such as visibility lidar and cloud lidar.The traditional polarization lidars use powerful pulsed laser and large diameter of telescope to improve the performance.However,it has reached its limit since the insufficient technical and technological.In this paper,the 1.5?m single photon detection technique is used to improve the performance of the polarization lidar.By increase the detection efficiency and reduce the detection noise,single photon detetors are able to greatly improve the signal-to-noise ratio of detection.Moreover,taking advantage of the ability to use the all-fiber optical path in the 1.5?m band,the polarization lidar is miniaturized and the airborne polarization lidar system is developed.It improves the portability of the polarization lidar and has a better vision compared to ground-based systems.In this paper,three sets of lidar systems based on single photon detectors were developed:1.aerosol and cloud lidar based on multimode InGaAs/InP single photon detector;2.polarization lidar based on superconducting nano wire single photon detector;3.UAV-borne polarization lidar.This dissertation proceeds as follows.1.An aerosol and cloud lidar based on MMF coupled InGaAs/InP single photon detector is developed.For Lidar applications,the operation parameters of single photon detector are optimized.The dead time and after-pulse probability of InGaAs/InP single-photon detectors are corrected in data processing to improve the dynamic response and signal-to-noise ratio.Continuous detection of atmospheric aerosols and clouds with high spatial and temporal resolution was achieved based on the multi-mode fiber coupled detector and a commercial 150mm telescope.The data shows that the multi-mode system has the ability to detect multiple layers of clouds.A comparative experiment was also designed using the same transmitter and single/multi-mode receiver.It was found that a lidar receiver based on a multi-mode coupled InGaAs/InP single photon detector can improve the signal-to-noise ratio by about 5 times.2.The first 1.5?m polarization lidar based on a superconducting nanowire single photon detector is demonstrated.The lidar fully utilizes the advantages of the superconducting nanowire single photon detector,and realizes a 48-hours detection of the atmospheric aerosol in Hefei City,which received density and depolarization ratio data with high spatial and temporal resolution.In this system,a time-division multiplexing module was developed.Only a single-channel detector was used to detect the two channel signals of the polarization lidar,which eliminated errors caused by fluctuations in detector efficiency and saved costs.This experiment successfully recorded an air pollution process in Hefei City in winter 2016,and monitored the process of a construction site emitting building dust.These data demonstrated the system's ability of monitoring and classifying air pollution.3.A compact polarization lidar for UAV-borne platforms is developed.The lidar uses an all-fiber structure and a compact transreceiver.With precision-designed mechanical,electrical,and thermal modules,a miniaturized system with a weight of 23 kg and a size of 60 cm ×50 cm×45 cm was achieved.In order to verify the lidar polarization recognition performance,the lidar first realized the intensity and depolarization imaging of the building on a ground scanning platform.The angular resolution of the lidar is 1/800 degree.Later,in cooperation with the Beihang Unmanned Helicopter Research Institute,flying experiments were conducted.In the experiment,the unmanned helicopter-driven lidar realized horizontal scanning,and obtained aerosol distribution images with a diameter of 12 km at different altitudes.