直视合成孔径激光成像雷达关键技术研究
文献类型：学位论文
| 作者 | 卢智勇 |
| 学位类别 | 博士 |
| 答辩日期 | 2015 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 刘立人 |
| 关键词 | 遥感 合成孔径激光成像雷达 直视合成孔径激光成像雷达 波面变换 电光调制 波前畸变 自差接收 成像信噪比 系统灵敏度 |
| 其他题名 | Research on Key Technologies of Down-looking Synthetic Aperture Imaging Ladar |
| 中文摘要 | 合成孔径激光成像雷达作为一种非常规的主动成像技术，可实现全天候、远距离高分辨、高视觉性及各种目标的快速成像，在军事、航天遥感、环境监测和气象观测等领域具有非常广泛的应用价值。合成孔径激光成像雷达的研究发展都是先复制微波波段的合成孔径激光成像雷达的基本原理和方法，其工作过程必须以侧视为必要条件，这种侧视合成孔径激光成像雷达的原理和方法决定了其在调制、解调和处理方面对于光信号的振幅、偏振、频率、时间相位和空间相位存在非常苛刻的要求，在保证拍频信号的初始相位严格同步和抑制非线性啁啾影响的相位控制技术上是相当复杂的，同时收发孔径的相互匹配使得大视场与高接收能量存在矛盾和制约，存在光学足趾小的缺点，这些因素严重影响了侧视合成孔径激光成像雷达的成像性能及其实用化。更重要的一点是侧视合成孔径激光成像雷达采用外差接收，受大气扰动、运动平台振动、目标散斑和激光雷达系统本身相位变换等影响是非常大的，在大气湍流对回波相位的影响超过波长量级的情况下，方位向聚集差，采用相位梯度自聚焦(PGA)算法也显得非常有限。因此，深入研究和发展合成孔径激光成像雷达，推进合成孔径激光成像雷达的工程化技术实现是一个十分重要的研究课题。 我们课题组通过采用自由空间波面变换的发射结构，自由空间的偏振型光学桥接器接收结构，可以有效地发挥光学上容易及灵活的波前变换和波面操控特性，创造性地提出了直视合成孔径激光成像雷达，其最大的优点是系统分辨率和光学足趾可自由设计，光学足趾可以很大，对于大气湍流等相位干扰具有自动消除的性能，具有巨大的实际应用价值。但直视合成孔径激光成像雷达的研究尚处于初级阶段，对于其波面变换的具体结构、波面像差的影响、是否存在其他工作模式以及高速波面操控的可能等关键技术问题还没有具体详细的研究。 本论文针对直视合成孔径激光成像雷达存在的上述问题，研究设计了多种具体的波面变换结构，模拟仿真了内发射场波前像差对成像的影响，提出了一种静态模式的直视合成孔径激光成像雷达，并搭建实验平台进行了实验室验证，此外还对基于LiNbO3晶体电光调制的直视合成孔径激光成像雷达的进行了初步探索研究。本论文的研究内容主要包括以下三个方面： (1)设计了多种直视合成孔径激光成像雷达的发射系统结构，并对这几种发射结构进行了分析比较，数值模拟仿真了其内光场的波面相位，部分给出了实际的干涉波面情况，最终采用双柱面镜联动扫描发射结构进行实验室10m平台的系统设计和搭建；同时仿真模拟了该结构内光场柱面镜不同波面像差对目标成像的影响情况，为进一步的成像实验提供了一定的参考价值。 (2)提出了一种静态模式直视合成孔径激光成像雷达，对静态模式直视合成孔径激光成像雷达进行了实验室验证，获得了预期的实验分辨率和成像结果；研究了提高系统灵敏度的方案，通过增加目标的辐射时间和提高采样率来提高成像的信噪比；最后利用正反扫描双图像的叠加来提高成像的信噪比，降低成像的散斑影响，这部分研究成果为直视合成孔径激光成像雷达的深入应用提供了有利的实验证据。 (3)开展了基于LiNbO3晶体电光调制的直视合成孔径激光成像雷达，设计了四种基于LiNbO3晶体电光调制的直视合成孔径激光成像雷达发射结构，同时在实验上对电光调制的波面变换器进行了初步的验证，验证其产生抛物波面相位情况及波前质量；同时对更大口径下的不同电极结构电光相位调制进行了实验研究，测量了其各自调制的波面相位，为高速电光调制直视合成孔径激光成像雷达的可能应用提供了前期的实验依据。 |
| 英文摘要 | Synthetic aperture imaging ladar (SAIL) is a non-traditional active imaging technology. It has advantages of all-weather imaging, long-distance, high-resolution, high visibility and fast imaging of all-kinds targets. It has wide application on the field of military, space remote sensing, environmental monitoring and meteorological observation. The technique of synthetic aperture imaging ladar was developed from the synthetic aperture radar (SAR) in radio frequencies. It must works in side-looking condition. The side-looking SAIL has the same princible and method with SAR, accordingly there are the rigorous constraints on the amplitude, polarization, frequency, temporal phase and spatial phase of optical signals in time domain and space domain during the signal collection and image construction. It is very complicated to control the strict initial synchronous phase of the beat frequency signal and to inhibit the nonlinear chirp signal. The large field of view and high receive enegies restricted each other duce to matched transmitting and receiving aperture. A narrow footprint is inherent to side-looking SAIL. Those factors limited the application of the SAIL. Moreover, the phase interferences from atmospheric turbulence and mechanical trembling in environments will seriously affect and even destroy the imaging. Phase gradient autofocus algorithm is also helplessness when the phase interferences exceed the wavelength. So the investigation of SAIL is a subject with great importance. The free-space SAIL was used by our research group. It contains free-space transmitting structure and free-space optical hybrid for conherent receivers. On the base of flexible free-space wavefront-controll technologies, down-looking SAILwas proposed creatively. Down-looking SAIL has its natural feature that the size of the optical footprint together with their associated imaging resolution is controllable and changedle in a large scale. And the influence from atmospheric turbulence and unmodeled line-of–sight motion can be automatically compensated. So it has significant value of practical application. However, many key technologies such as detailed structure of wavefront transformation, influence of wavefront aberration, other operational mode and high-speed wavefront transformation have not been proposed yet. In this thesis, the detailed structures of wavefront transmation are designed. Influence of inner wavefront aberration on down-looking SAIL imaging is investigated. A new static-mode down-looking SAIL is proposed and verified in table-top laboratory. In addition, down-looking SAIL based on the LiNbO3 crystal electro-optical modulation is explored. The most work can be presented as: (1)Many kinds of transmitters applying to down-looking SAIL are designed. Those transmitters are contrastive analysis and numerical simulation. Some of those structures are showed the interference pattern. The transmitter with the linked scanning of two cylindrical lenses is selected to set up the experimental system. At the same time, the influence of inner wavefront aberration on down-looking SAIL imaging is researched. It provides some reference value for further imaging experiment. (2)A static-mode down-looking SAIL in which the target and carrying-platform are kept still during the collection process is proposed and demonstrated. The achieved imaging resolution is in agreement with the theoretical design. The improvement of system sensitivity is investigated. Signal to Noise Ratio (SNR) is improved by the increasing irradiation time and increasing the sampling rate. At last, the double image from positive direction scanning and negative direction scanning in cross direction of travel are overlayed to improve imaging SNR and decrease the speckle effect. These results provide previous experimental proof for further application of down-looking SAIL. (3)Down-looking SAIL based on the LiNbO3 crystal electro-optical modulation is investigated. Four kinds of transmitters with LiNbO3 crystal electro-optical modulation are designed. The electro-optical parabolic wavefront is confirmed by the systematical experiments. The measuremental parabolic wavefront agrees with the theoretical value and controlled accurately. Then, the phase of the bigger aperture LiNbO3 crystal modulation with different electrod type is also measured by the digital holographic interferometry. These important experimental proofs are supported for the possible application of no-mechanical scanning down-looking SAIL. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15942]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 卢智勇. 直视合成孔径激光成像雷达关键技术研究[D]. 中国科学院上海光学精密机械研究所. 2015. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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