Laser Multi-layer Cladding Experiment on the DD3 Single Crystal Using FGH95 Powder:Investigation on the Microstructure of Single Crystal Cladding Layer

Laser multi\|layer cladding experiments were performed on the substrate of DD3 single crystal with FGH95 powder as cladding material.The solidification microstructure in the sample was investigated.It was found that the solidification microstructure was greatly influenced by the crystallography orientation of the substrate and the local solidification conditions.When the angle between the preferred orientation of the single crystal and the direction of heat flow in the cladding layer is less than 30°,single crystal cladding layers were acquired.Otherwise the crystallography orientation of the cladding layer will deviate from the orientation of the substrate and the microstructure with polycrystalline appears.Meanwhile,even when the experiments were performed on the same preferred crystal surface,the solidification microstructures will be different distinctly resulting from the variation of the local solidification conditions.The secondary arms were degenerated and the primary arm spacing was about 10\|20μm.Further investigation shows that the phases of the cladding layer are mainly made up ofγ,γ′,the flower\|likeγ/γ′eutectic and carbide.The morphology ofγ′was cubical and the size is less than 0.1μm.

DETECTION ON MICRO-DOPPLER EFFECT BASED ON LASER COHERENT RADAR

A laser coherent detection system of 1550 nm wavelength was presented, and experimen- tal research on detecting micro-Doppler effect in a dynamic target was developed. In the study, the return signal in the time domain is decomposed into a set of components in different wavelet scales by multi-resolution wavelet analysis, and the components are associated with the vibrational motions in a target. Then micro-Doppler signatures are extracted by applying the reconstruction. During the course of the final data processing frequency analysis and time-frequency analysis are applied to analyze the vibrationM signals and estimate the motion parameters successfully. The experimental results indicate that the system can effectively detect micro-Doppler information in a moving target, and the tiny vibrational signatures also can be acquired effectively by wavelet multi-resolution analy- sis and time-frequency analysis.

Dynamic obstacles detection of tram based on laser radar

The detection of obstacles in a dynamic environment is a hot and difficult problem.A method of autonomously detecting obstacles based on laser radar is proposed as a safety auxiliary structure of tram.The nearest neighbor method is used for spatial obstacles clustering from laser radar data.By analyzing the characteristics of obstacles,the types of obstacles are determined by time correlation.Experiments were carried out on the developed unmanned aerial vehicle(UAV),and the experimental results verify the effectiveness of the proposed method.

Digital Receiver for Laser Imaging Radar

With the extension of the application domains for laser imaging radar, it is necessary to find a new technical way to obtain high technical performance and adaptive ability. In this paper, A new concept of digital receiver of laser imaging radar system is presented. This digital receiver is defined as a time varying parameter receiver which possesses large dynamics region and time domain filter. The receiver’s mode, component structure as well as every function of its processing are described. The results and laboratorial data show the feasibility of digital reception. Also, it can exploit the inherent nature of laser imaging radar to obtain high probability of detection.

Building of road boundary map based on laser radar

A method for road boundary detection and tracking using laser ladar with respect to a vehicle＇ s local coordinates is proposed. It can be applied to different types of road conditions, such as roads with or without curbs, having relatively rough road surface and with obstacles on road surface. In the method, some line segments are extracted after a series of preprocessing on range data. The extracted line segments are combined and further selected. They are then united to match the road models and generate the road boundary points which are tracked by Kalman filter. Then the obtained road boundary points are transformed to build a precise vector map by least squares fitting algorithm. These fitted line segments represent road boundary vectors. The vector map is precise enough to provide ample road information such as the orientation of road, the road width and the passable road region. Finally, extensive experiments conducted in urban and semi-urban environment demonstrate the robustness, effectiveness and viability of the proposed method.

Application Research on Space Laser Communication in Bistatic Radar System

There exist three synchronizing problems in the bistatic radar system that some signals of the radar receiver must be synchronized with those of the radar transmitter. Several methods realizing data transmission, which are used to complete the synchronization existing in the bistatic radar system, are described. Then a new idea is brought forward that employs space laser communication in the bistatic radar system to realize its data transmission. The theoretic analysis of the idea's usability and its merits are discussed in details. Finally the latest development of space laser communication is introduced, and the utility of the idea is pointed out further.

Comparative research and its significance of deformation measurements by technologies of laser real-time holographic interferome-try and radar differential interferometry

The principles and applications of laser real-time holographic interferometry （LRTHI） and radar differential interferometry （RDI） technologies are described in this paper, respectively. By using LRTHI, we can observe the deformation of samples under pressure in the lab and study the anomaly characteristics relating to different strain fields in different fracture-developing areas; while by using RDI, we can observe the landform and surface deformation. The results of deformation observed before and after the Ms=7.9 Mani earthquake （Tibet） and Ms=6.2 Shangyi-Zhangbei earthquake in China are obtained. It is pointed out that LRTHI and RDi are similar, which study the characteristics of anomalous deformation field by fringe variations for both of them. Therefore, the observation of deformation field in the seismogenic process, especially in the period impending an earthquake by RDI, and the comparative study in the lab by LRTHI are of great significance.

High Accuracy and Real-Time Gated Viewing Laser Radar

A gated viewing laser radar has an excellent performance in underwater low light level imaging, and it also provides a viable solution to inhibit backscattering. In this paper, a gated viewing imaging system according to the demand for real-time imaging is presented, and then the simulation is used to analyze the performance of the real-time gated viewing system. The range accuracy performance is limited by the slice number, the width of gate, the delay time step, the initial delay time, as well as the system noise and atmospheric turbulence. The simulation results indicate that the highest range accuracy can be achieved when the system works with the optimal parameters. Finally, how to choose the optimal parameters has been researched.

Path Planning Approach Based on Dual Laser Radar Fusion

A dual laser radar based path planning method for mobile robot in general outdoor road environment is proposed. Firstly, the point-wise sequence and target library of the global optimal path are generated based on algorithm A*. Secondly, the local target information and the perceptive information from dual laser radar are combined, and the different field information from both horizontal and aslant fixed laser radars is fused. Finally, the optimal driving angle is computed by the improved angle potential field(APF)algorithm. The practical experiment results validate the robustness and timeliness of the proposed approach.

Noise Temperature Characteristics and Gain-control of Avalanche Photodiodes for Laser Radar

Avalanche photodiodes(APDs) are promising light sensors with high quantum efficiency and low noise. It has been extensively used in radiation detection,laser radar and other weak signal detection fields. Unlike other photodiodes,APD is a very sensitive light detector with very high internal gain. The basic theory shows that the gain of APD is related to the temperature. The internal gain fluctuates with the variation of temperature. Investigated was the influence of the variation of the gain induced by the fluctuation of temperature on the output from APD for a very weak laser pulse input in laser radar. An active reverse-biased voltage compensation method is used to stabilize the gain of APD. An APD model is setup to simulate the detection of light pulse signal. The avalanche process,various noises and temperature's effect are all included in the model. Our results show that for the detection of weak light signal such as in laser radar,even a very small fluctuation of temperature could cause a great effect on APD's gain. The results show that the signal-to-noise ratio of the APD's output could be improved effectively with the active gain-control system.

Design of Laser Radar Fiber Optic Liquid Level Sensor System

A novel fiber optic liquid level sensor based on laser radar (ladar) is reported here. Using the perfect technique of ladar in which the phase of amplitude modulated light wave reflected from the liquid surface is compared with that of original modulation signal, the distance can be measured precisely. A special symmetric compensating coaxial optical system is proposed to eliminate many adverse effects. It realized the one-time electronic-free optical measurement on a simulated oil tank and achieves an accuracy of 0.3%, within a temperature range of -10 ℃～+40 ℃ over a measuring of 0～10 m.

Parameter Inversions of Multi-Layer Media of Mars Polar Region with Validation of SHARAD Data

HF (high frequency) radar sounder technology has been developed for several missions of Mars surface/subsurface exploration. This paper presents a model of rough surface and stratified sub-surfaces to describe the multi-layer structure of Mars polar deposits. Based on numerical simulation of radar echoes from rough surface/stratified interfaces, an inversion approach is developed to obtain the parameters of Polar Layered Deposits, i.e. layers thickness and dielectric constants. As a validation example, the SHARAD radar sounder data of the Promethei Lingula of Mars South Polar region is adopted for parameters inversion. The result of stratification is also analyzed and compared with the optical photo of the deep cliff of Chasma Australe canyon. Dielectric inversions show that the deposit media are not uniform, and the dielectric constants of the Promethei Lingula surfaces are large, and become reduced around the depth of 20 m - 30 m, below where most of the deposits are nearly pure ice, except a few thin layers with a lot of dust.

Design and Tests of A Cable Detection Laser Imaging Radar System

Rotorcraft in low-level flight is endangered by power lines or telephone wires. The development of automation tools that can detect obstacles in the flight path and warn the crew would significantly reduce pilot workload and increase safety. Therefore, a cable detection radar system is developed The real-time dynamic imaging synchronizing with radar space scanning has been implemented in developed ladar system. The requirements of the flight mission to prevent ＂wire strike＂ are analyzed and estimated, the advantages and disadvantages of the millimeter wave system with the laser system are weighted The result shows that Laser system is the best suited for helicopter avoidance obstacle. In addition, several design gist of detecting wire radar that was used in the developed ladar system is proposed and the developed zero backlash imaging technology and several advanced warning function are described. The detailed results of system ground tests and the performances description are presented The ground test of the developed ladar system has demonstrated that the developed imaging ladar system performance can achieve and satisfy the requirements of the mission to prevent ＂wire strike＂.

基于激光雷达扫描的料仓原料储料量测量方法

为提高仓内原料储料量测量自动化和智能化水平,设计了一种基于二维激光雷达扫描的储料量测量装置与系统。本系统采用RPLIDARS1型二维激光雷达扫描获取不同储料量物料的原始点云数据,通过坐标变换、重叠点提取、滤波、分割等方法对原始点云进行预处理,采用贪婪投影三角化算法将预处理后的点云进行三维重建,获得仓内原料的三维模型,结合物料三维模型和物料的容重获得仓内原料的储料量,从而实现储料量的自动测量。以玉米为试验对象,测量小型储料塔内玉米储料量并对玉米不同储料量进行扫描测量,验证模型的准确性,结果显示:测量结果的平均绝对误差为8.05kg,平均相对误差为1.52%。研究结果表明,基于二维激光雷达扫描的储料量测量方法是可行的,具有较好的稳定性和测量精度,能够满足实际生产需求。

基于微型激光雷达的无人机智能化电力线路巡检技术研究

介绍了一种利用激光探测和测距(LiDAR)进行实时电力线检测的算法,并且对微型激光雷达无人机进行电力线路巡检抽象建模。通过使用平面分析法对巡检现场进行距离的比较来分割点云,并提取一组电力线候选点,这些点被拟合到线段上,线段根据它们的共线性质进一步分组比较。该方法可利用图像的共线特性完成特征检验,并在光线条件差以及线路背景复杂的环境下仍可获得较为可靠的巡检结果。案例中电力线路垂直平均误差最大为0.49 m,其他所有直线的估计平均误差都小于0.07 m,水平拟合时,所有平均误差都在0.14 m以内。验证了所提出基于微型激光雷达的无人机技术进行电力线路智能化巡检方法的有效性与可行性。

基于激光雷达的自主移动机器人实验教学平台设计

为培养高素质复合型的“新工科”人才,满足相关课程的实验教学需求,设计了基于激光雷达的自主移动机器人实验教学平台。平台涉及机械设计、机器人操作系统开发、同时定位与地图构建(SLAM)、路径规划等相关理论知识。利用平台开发了Rviz可视化界面、SLAM仿真、室外建图、路径规划等实验项目。实验结果表明,自主移动机器人软硬件系统的基本性能良好,相关SLAM算法、路径规划方法具有可行性。通过该平台开展实验教学,可以显著提升学生解决工程实际问题能力和创新实践能力。

室内巡检机器人的定位方法

针对巡检机器人在室内环境进行巡检任务时无法准确到达指定位置的问题,提出一种基于激光雷达和里程计的分区域定位方法。当机器人工作在定位精度要求不高的非目标区域时,采用激光雷达加里程计的定位算法进行导航;而当机器人进入包含指定位置的目标区域时,则利用搭载在机器人上的激光测距传感器和已知位置的地标来推算机器人的当前位姿,并根据机器人的当前误差进行位姿矫正,实现机器人在目标位置的精确定位。实验结果表明:该定位方法的位置误差<2 cm,偏转角误差<1°,满足巡检机器人的定位精度要求,具备可行性和实际价值。

盖革APD激光雷达高空间分辨率三维重构方法研究

盖革模式阵列APD激光雷达由于像元数的限制导致重构的三维距离像分辨率低,严重限制了对场景信息的感知识别能力。为此,提出一种基于改进图像引导的盖革模式阵列APD激光雷达超分辨三维图像重构算法。主要研究基于配准后的盖革APD低分辨距离图像、增强电荷耦合器件(ICCD)相机高分辨强度图像和马尔科夫随机场模型,建立具有距离保真项和正则化项约束的全局能量函数,最终对优化模型的最优化求解实现高分辨强度图像对低分辨距离图像的超分辨引导重构。实验结果表明,相较于现有算法,文中算法在提升重构三维图像分辨率的同时,也使图像的边缘更加锐利。该研究对于盖革模式阵列APD激光雷达的目标探测、识别和跟踪具有重要意义。

基于ConvLSTM的飞机发动机喷流时空预测

为探究起飞飞机发动机喷流对后侧穿越飞机的影响程度,提出一种基于卷积长短时记忆网络(ConvLSTM)的飞机发动机喷流预测模型,旨在预测未来某一时段的流场数据。通过激光测风雷达采集飞机发动机喷流数据并进行预处理。分别采用时间子网和空间子网捕捉飞机发动机喷流的时间和空间结构特征。通过融合时空特征,使用全连接层输出未来流场数据,以此构建卷积长短时记忆网络面向飞机发动机复杂喷流数据的未来帧预测。结果表明:ConvLSTM模型能够准确地预测出飞机发动机喷流的时空分布,取得RMSE12.28和MAE9.26的实验结果,较传统神经网络模型预测结果拥有更稳定的RMSE值及预测精度,有效提高了喷流时空预测的质量和精度,为研究飞机发动机喷流影响范围提供支撑。

无人驾驶车辆感知空间的构建及可感知性判别

无人驾驶车辆的传感器代替人眼感知道路空间的信息,保障一定感知空间的可感知性,是无人驾驶安全运行的重要前提。因此,该文在国内外研究文献调研以及相关软硬件技术分析的基础上,分析了当前无人驾驶车辆感知技术的局限性,包括激光雷达、摄像头和毫米波雷达等传感器的识别范围和特性;利用激光雷达和组合导航系统对道路的现实信息进行采集,进一步利用收集到的点云数据、定位信息、同步定位与建模算法构建无人驾驶车辆的三维感知空间,实现了道路的三维数字模型构建。同时在三维点云地图中进行测距能力、水平视场角和垂直视场角等参数数学表达模型构建,利用空间坐标变换方法,将传感器识别范围内的三维点云数据进行分离,并转换到统一的坐标系下。最后利用Delaunay三角化方法,构建出能够反映感知空间特性的三维模型,从而实现三维感知空间的可感知性的判定方法。为验证该文方法的实用性和准确性,利用实地采集的数据对算法进行了测试。测试结果表明,该文提出的方法具有良好的鲁棒性,能够在复杂的道路环境中稳定工作,可以准确评估无人驾驶车辆的感知能力。这一研究成果不仅为无人驾驶车辆的道路设计和安全评估提供了科学依据,也为无人驾驶技术的进一步发展和应用提供了强有力的技术支持。