The characteristics of aerosol optical depth (AOD), Ångström exponent α, water vapor content and turbidity coefficient were analyzed by using the latest observation data of CE318 Sun-photometer in the southern suburb of Xi’an between December 2019 and November 2020. In addition, the frequency distribution and aerosol types were studied, and the influencing factors were analyzed briefly. The annual mean value of AOD in the southern suburb of Xi'an was 0.529±0.358, and the distribution of frequency was unimodal. The values of AOD in winter and spring were higher than that in summer and autumn. The annual mean value of α was 0.894±0.373, and the distribution of frequency was multipeak distribution. The number of the α value lower than 0.5 in spring was significantly higher than that in the other three seasons, which was caused by the influence of coarse mode particles, while the other seasons were affected both by coarse and fine mode particles. It can be seen that different types of aerosols are mixed in Xi’an. The influence of Desert Dust Aerosols in spring is greater than that in other seasons. Biomass Burning/Urban Industry Aerosols (BB/UI) are the main types in autumn and winter, and all types of aerosols are relatively balanced in summer.
To improve the performance of laser scanning 3D imaging, a new multi-beam imaging method based on the fiber-type optical phased array (OPA) is proposed. In the system, the fast scanning multiple beams, coherently combined from the fiber-type OPA, are employed to cover the whole field-of-view (FOV), and each sub-beam is only responsible for a small local FOV; in the meanwhile, a low-pixel APD array is utilized to receive the echoes from the target in the FOV, each pixel of which is also for a corresponding local FOV. Consequently, making use of fast multi-beam scanning and an APD array detector, a fast and high-resolution imaging can be obtained. In this paper, the imaging principle using the multibeam scanning of fiber-type OPA will be first introduced, and then the principle of high-resolution imaging with a lowpixel APD array detector is illustrated. Finally, the 3D imaging experiment of model targets with a proof-of-concept system is presented.
In this paper, we focus on the performance improvement of the free space optical communication system and carry out the research on wavefront-sensorless adaptive optics. We use a phase only liquid crystal spatial light modulator (SLM) as the wavefront corrector. The optical intensity distribution of the distorted wavefront is detected by a CCD. We develop a wavefront controller based on ARM and a software based on the Linux operating system. The wavefront controller can control the CCD camera and the wavefront corrector. There being two SLMs in the experimental system, one simulates atmospheric turbulence and the other is used to compensate the wavefront distortion. The experimental results show that the performance quality metric (the total gray value of 25 pixels) increases from 3037 to 4863 after 200 iterations. Besides, it is demonstrated that our wavefront-sensorless adaptive optics system based on SPGD algorithm has a good performance in compensating wavefront distortion.
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