| 题名 | 近海激光通信大气影响分析及抑制方法研究 |
| 作者 | 高世杰 |
| 学位类别 | 博士 |
| 答辩日期 | 2015-05 |
| 授予单位 | 中国科学院大学 |
| 导师 | 吴志勇 |
| 关键词 | 近海激光通信 折射率结构常数 双波段测量 多发多收 通信链路功率 |
| 其他题名 | Reserch on Atmospheric influence and mitigation technology in near sea level laser communicaton |
| 学位专业 | 电路与系统 |
| 中文摘要 | 由于激光通信系统具有宽频带、高速率、抗截获能力强、抗干扰能力强和轻小型等突出优点，使其非常适合深空、星际、星地、空空、空地等链路通信，因此在近年来备受关注。随着我国海洋军力不断发展，激光通信系统在船与船、船与岸间的应用前景日趋广阔。同深空、星际、空空等应用环境不同，船用激光通信的信号传输媒介是位于海面上方十几米至几十米的大气，由于这一区域的大气衰减和大气湍流对通信链路保持和通信质量有着严重的干扰。因此本文通过理论分析与实验验证，对近海激光通信大气影响进行了分析，对抑制大气影响的方法展开研究。 首先，在介绍本文研究所面向的近海大气激光通信系统的组成和工作原理的基础上，分析了近海大气激光通信系统的链路模型与影响通信质量的关键大气参数估算模型，重点分析了吸收效应、散射效应和折射率起伏所引起的闪烁和漂移效应。 其次，为了定量评估大气衰减与大气湍流对近海激光通信的影响，设计了对几项关键大气参数的测量方案。采用850nm和1550nm两个波段的激光进行同步测量，给出了测量原理和方案，测量内容主要包括：采用光功率计测量大气吸收效应中的消光系数；采用短波红外相机测量激光光斑的闪烁指数和到达角起伏方差。在获取全天时测量数据后，计算对1550nm波段激光成像的闪烁指数和到达角起伏方差，将其代入大气折射率结构常数经典计算方法中，演算出850nm波段激光图像中目标的闪烁指数和到达角起伏方差，并将所得结果与实测同步850nm激光光斑图像进行比对。依据以上数据分析结果，在国内外学者的研究改进基础上，进一步修正塔塔尔斯基提出的平面波闪烁模型，并推导了其在改进型Hill谱和Von Karman谱下的公式，同时改进了美国海军实验室所采用的到达角起伏所引起的漂移模型，使其更适合描述任务海域海面大气环境。 再次，本文针对大气对通信链路的稳定和通信质量的影响分别提出了抑制方法。近海大气激光通信的链路稳定主要依赖于系统对激光光斑的捕获、跟踪和瞄准（Acquisition，Tracking and Pointing，ATP），ATP系统对激光的定位一般采用CCD等光学成像器件，当激光通信链路经过大气时，由于受大气的影响，ATP系统所获得的激光光斑图像是退化后的图像，会导致跟瞄精度下降甚至无法完成对目标的捕获。工程中常用形态学滤波方法，该方法相对计算量较小，易于硬件系统实现，但算法本身的物理意义并不是恢复光斑的原有形状和位置。近年来常用的自适应光学方法已普遍用于大口径天文观测中，但对于高频率的激光通信应用而言，还缺少充分的实验验证，而且自适应光学系统技术复杂，成本高昂。 因此本文针对激光通信系统光斑图像受大气湍流影响的问题，通过改进约束共轭梯度迭代算法，提出激光光斑退化图像的快速盲复原方法，在对光斑图像进行快速复原的基础上，对光斑目标进行分割，并通过连通域计算实时提取复原后的光斑中心位置信息，提高ATP系统对光斑中心位置的提取精度。 在抑制大气对通信质量的影响方面，本文提出了基于实时图像处理技术的分集接收方案，通过2个配有150mm口径镜头的短波红外相机和配有等效大口径镜头的红外相机同步采集光斑图像，并将数据按照之前所提的量化方法进行分析和比对，验证分集接收对大气影响的抑制作用。 最后，通过设计市内2.1km和近海面8.9km激光通信实验，理论分析结合实测数据，以通信误码率、接收光功率等参数为依据，通信链路接收光功率理论分析和实测数据互相关性达到70%，一致性较好，从而验证本文所提出的改进后大气参数估算模型的准确性，以及盲解卷积算法的有效性，继而为后续工程实践提供有力支撑。 |
| 英文摘要 | Because the laser communication system has the advantage of high bandwidth, high speed, strong anti-interception ability, strong anti-interference ability and small light, it is very suitable for deep space, star to star, air to air and air to ground link communication. Therefor it has attracted much attention in recent years. With the continuous development of China's marine forces, the application prospect of laser communication system on the ship to ship, ship to shore is more and more broad. Compared with the deep space, star to star, air to air and other different application environments, signal transmission mediumof ship borne laser communication device is the atmosphere located above the sea of tens of meters. The atmospheric attenuation and atmospheric turbulencein the area has serious interference to the keep of communication link and communication quality. Therefore, the theoretical analysis and experimental verification was carried out in this paper, the atmosphere influence of offshore laser communication was analyzed, the method of inhibiting atmosphere effect was studied. Firstly, on the basis of introducing the composition of offshore atmospheric laser communication systemand working principle, the link model of offshore atmospheric laser communication system and the key atmospheric parameters estimation model which influence the quality of communication were analyzed in this paper, focused on the analysis of the absorption effect, scattering effect and flickering and drifting effect caused by refractive index fluctuation. Secondly, in order to evaluate the influence of atmospheric attenuation and atmospheric turbulence to offshore laser communication, measurement scheme of several key atmospheric parameters was designed. Measuring principle and scheme were proposed using simultaneous measurement of two band laser, 850nm and 1550nm.The measurementmainly includes: using optical power meterto measurethe extinction coefficient of atmospheric absorption effect; using near infrared camera to measure the scintillation index of laser spot andthe angle of arrival fluctuation variance. After obtaining the measurement data of all time, the scintillation index and the angle of arrival fluctuation variance of 1550nm wave band laser image can be calculated. Putting the calculation results in the classical calculation method of the atmospheric structure constant of refractive index, we can get the scintillation index and the angle of arrival fluctuation variance of the target in 850nm wave band laser image, and then get the comparison result between thecalculated result andthe measured synchronous 850nmimageof laser spot.Based on the results of above data analysis, and on the basis of the domestic and foreign scholars’study and improvement, the paper further modified plane wave scintillation model proposed by Tatarskii, and derived theformula in improved Hill spectrum and Von Karman spectrum, and also improved the drift model caused by the angle of arrival fluctuation used in the U.S. Naval Research Laboratory, to make it more suitable to describethe sea surface atmospheric environment in task area. Thirdly, suppression methods were proposed respectively aiming at the effect of the atmosphere on the stability of communication link and the quality of communication.Link stability of offshore atmospheric laser communication mainly rely on the acquisition, tracking and pointing(ATP) of the system to the beacon. The ATP positioning system for laser generally used the CCD optical imaging device.When the laser communication link passed through the atmosphere, due to the influence of the atmosphere, the laser spot image acquired by the ATP system was degraded image.It wouldcause the tracking and pointing precision drops, even make it unable to complete the acquisition. The morphological filtering method was commonly used in engineering, this method needed relatively smaller amount of calculation, and was easily implemented by hardware system, but the physical meaning of algorithm itself did not restore the original shape and positionof the spot. In recent years, the commonly used method of adaptive optics had been widely used in large aperture astronomical observation, but for high frequency laser communication, there was lack of adequate experimental validation, and the technology of adaptive optics system was complexand cost highly. So this paper researched on the problem of the laser communication system beacon image influenced by atmospheric turbulence, through improved constrained conjugate gradient iterative algorithm.It proposed a fast blind restoration method of degraded laser spot image. On the basisof rapid recovery in the spot image, the spot target was segmented, and the connected domain was calculated to extract recovery spot center location information in real time to improve extraction accuracy of ATP system on the spot center. In the inhibitory effect of the atmosphere on the quality of communication, this paper presented a diversity receiving scheme using real-time image processing technology. 2 near infrared cameraswith 150mm aperture lens and infrared camera with large aperture lens were used to acquirespot image synchronously, and the datawas analyzed and compared by the previously mentionedquantitative method, to verify the inhibition effect ofdiversity reception on the atmospheric influence. Finally, through the laser communicationexperiment of 2.1 km in the city and 8.9 km near the sea surface, theoretical analysis combined with experimental data was used.According to the parameters, such ascommunication error rate, receiving light power, the communication link receiving light power between theory analysis and the measured data was up to 70% with high consistency. The accuracy ofthe proposed improvement of atmospheric parameters estimation model and the effectiveness of the blind deconvolution algorithm were verified to provide powerful support for the follow-up project practice. |
| 公开日期 | 2015-12-24 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.ciomp.ac.cn/handle/181722/48838]  |
| 专题 | 长春光学精密机械与物理研究所_中科院长春光机所知识产出 |
| 推荐引用方式 GB/T 7714 | 高世杰. 近海激光通信大气影响分析及抑制方法研究[D]. 中国科学院大学. 2015. |
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