面向森林植被的星载大光斑激光雷达回波仿真

利用星载激光雷达的大光斑全波形数据估测植被结构参数、监测森林生态已受到广泛关注。为了更准确地理解森林植被的结构参数和光学特性对激光雷达回波波形的影响,利用实测森林植被数据提取植被空间分布的统计规律,考虑地形坡度变化和植被冠层反射特性的影响,生成参数化的森林植被空间轮廓反射模型,结合星载激光雷达的回波理论,建立了面向植被的星载激光雷达波形仿真器。由大兴安岭地区的实测植被数据提取的统计规律生成的森林目标仿真波形与地球科学激光测高仪系统（Geoscience Laser Altimeter System,GLAS）真实回波波形具有较好的一致性,平均相关系数R2达到0.91。通过波形仿真分析发现,光斑尺寸减小有利于大坡度地形的森林信息反演,研究成果对中国未来研制星载激光雷达载荷的系统参数设计具有参考意义。     

资源三号02星激光测高仪足印位置预报方法

激光测高仪在轨几何检校是提高激光点平面和高程精度的必要途径,而激光足印地准确捕获是成功开展激光测高仪在轨几何检校的前提。本文针对资源三号02星搭载的我国首台激光测高仪的在轨几何检校试验需要,在参考光学遥感卫星成像几何模型的基础上,提出并构建了一套严密的激光足印位置预报模型。该模型充分顾及卫星平台在轨运行规律及激光与卫星相对几何关系,建立了激光发射点到地面足印的严密几何定位预报模型,通过金字塔地形匹配、基于加速度轨道预测以及频率域姿态分析分别获取预估的激光指向、轨道位置和姿态信息,实现地面激光足印的位置预报。该模型已应用于资源三号02星激光测高仪在轨几何检校试验中,预报的激光足印位置与探测器捕获到的实际位置的最大误差小于150m,充分验证了预报模型的正确性,实现了我国遥感卫星从天上到地面点对点的精确预报,为国产激光测高仪在轨几何检校提供了有力的技术支撑。     

林木空间格局对大光斑激光雷达波形的影响模拟

激光雷达是近年来国际上发展十分迅速的主动遥感技术，在森林参数的定量测量和反演上取得了成功应用。激光雷达具有与被动光学遥感不同的成像机理，对植被空间结构和地形的探测能力很强。大光斑激光雷达系统一般指光斑直径在8—70m、连续记录激光回波波形的激光雷达系统。由于大光斑连续回波的激光雷达的光斑尺寸通常大于林木冠幅，波形中往往包含了森林冠层和许多森林元素的信息而不仅仅是单株树的信息。对于搭载在ICESAT卫星上的GLAS而言，光斑直径为70m，因此光斑对应着一片森林，包括很多棵树，在GLAS的激光光斑内树木的空间分布会有一定变化。同时激光雷达发射的脉冲信号在激光光斑内的分布也不均匀，而是从中心到边缘呈递减的分布。因此树木空间分布模式的变化对波形会产生一定的影响。通过对几种典型的树木空间格局进行模拟（包括规则分布、均匀（随机）分布和集群分布），假定激光光斑内能量呈高斯分布，模拟了各种树木分布模式林分的激光雷达信号。从模拟结果可见，森林的空间分布模式对大光斑激光雷达波形有明显的影响，对于波形面积（AWAV）和波形半能量高度（HOME），规则分布〉随机分布〉团状分布。其中对于HOME而言，规则分布和随机分布十分接近，而对于AWAV而言，聚集中心的变动不太敏感。     

资源三号02星对地激光测高系统几何检校及验证

星载激光测高仪安装误差、激光指向和激光测距误差等导致最终激光测高精度不高,对激光器进行在轨几何检校可以有效提升激光测高精度。针对资源三号02星（ZY3-02）激光测高仪的工作模式,以裸露地表的航天飞机雷达地形测绘任务（shuttle radar topography mission,SRTM）数字高程模型（digital elevation model,DEM）数据约束同轨激光测距值,通过逼近地形起伏趋势线实现了卫星激光器出射方向的初始检校,实验证明不同轨激光指向的相对检校精度在20 m以内。利用地面铺设激光靶标的方法对星载激光测高系统进行几何精检校,并通过外业测量验证了ZY3-02激光器在平坦区域的测高精度优于0.5 m。     

资源三号02星激光测高仪在轨几何检校与试验验证

我国在资源三号02星上首次搭载了一台用于对地观测的试验性载荷——激光测高仪,开展对地观测的激光测高试验。由于卫星发射时的振动以及入轨后空间环境变化等因素影响,激光测高仪的指向、测距等系统参数相对于发射前地面测量值可能发生变化,从而引起激光的平面和高程误差。本文根据资源三号02星激光测高仪特点,提出了一种基于地面探测器的在轨几何检校方法,该方法构建了以指向、测距为系统误差的严密几何检校模型,以激光测距值残差最小为原则,利用地面探测器捕获的激光光斑位置作为参考,实现系统误差参数高精度在轨几何检校。利用卫星在轨测试期间多个试验场数据进行检校后,以有关DEM数据作为地面参考比对,地形坡度小于2°区域内的激光点高程精度由检校前的100~140m提高到2~3m。利用平坦地区激光足印内少量GPS外业控制点进行验证对比,检校后激光高程测量的绝对精度优于1m。试验结果表明了资源三号02星激光测高仪在轨几何检校方法的有效性和正确性。     

影响机载激光扫描测高精度的系统误差分析

简要介绍了机载激光扫描测高技术的系统组成和发展现状。通过坐标转换技术建立起机载激光扫描对地定位的基本几何关系,并从这些几何关系出发,着重分析了动态偏心改正及动态时效误差对机载激光测高精度的影响,对不同的误差源如何影响定位结果的精度进行了讨论,最后给出模拟计算结果,得出了一些有益的结论。     

Analysis of systematic error influences on accuracy of airborne laser scanning altimetry

The error sources related to the laser rangefinder, GPS and INS are analyzed in details. Several coordinates systems used in airborne laser scanning are set up, and then the basic formula of system is given.This paper emphasizes on discussing the kinematic offset correction between GPS antenna phase center and laser fired point. And kinematic time delay influence on laser footprint position, the ranging errors, positioning errors, attitude errors and integration errors of the system are also explored. Finally, the result shows that thekinematic time delay can be neglected as compared with other error sources. The accuracy of the coordinates is not only influenced by the amplitude of the error, but also controlled by the operation parameters such as flight height, scanning angle amplitude and attitude magnitude of the platform.     

Analysis of systematic error influences on accuracy of airborne laser scanning altimetry

The error sources related to the laser rangefinder, GPS and INS are analyzed in details. Several coordinates systems used in airborne laser scanning are set up, and then the basic formula of system is given. This paper emphasizes on discussing the kinematic offset correction between GPS antenna phase center and laser fired point. And kinematic time delay influence on laser footprint position, the ranging errors, positioning errors, attitude errors and integration errors of the system are also explored. Finally, the result shows that the kinematic time delay can be neglected as compared with other error sources. The accuracy of the coordinates is not only influenced by the amplitude of the error, but also controlled by the operation parameters such as flight height, scanning angle amplitude and attitude magnitude of the platform.     

资源三号02星激光测高数据质量分析

近几年来,中国的对地观测卫星激光测高技术发展较快,资源三号02星上搭载了国内首台对地观测的卫星激光测高试验载荷,在后续的高分七号、陆地生态系统碳监测卫星上均装备业务化应用的激光测高仪,开展国产对地观测卫星激光测高数据质量分析研究非常必要,能有效填补国内空白并推动相关技术发展。本文对资源三号02星载荷的激光测高数据进行了严密几何处理,重点从夜间观测、卫星小角度侧摆、海面区域等不同条件下的数据质量进行了分析,对数据的平均可用率进行了统计分析。试验表明,资源三号02星激光测高仪能获得约30%有效测高数据,在夜间数据有效利用率略有提高,在大型水面也能获得有效数据,经后处理后在平坦地区验证的绝对高程精度优于1.0 m,部分点高程精度优于0.5 m,硬件本身的测距精度和卫星姿态测量误差是主要的误差源。相关结论对于后续国产卫星激光测高载荷的研制以及数据后处理和应用具有参考价值。     

Real-time registration of airborne laser data with sub-decimeter accuracy

This paper presents a methodology for the precise registering of airborne laser data directly in flight with an accuracy that is sufficient for the majority of derived products, such as digital terrain models. We first present the strategy that integrates GPS/INS/LiDAR data for generating laser point clouds directly in flight and analyzes their accuracy. The latter requires the implementation of a functional covariance propagation on-line for all the system components (i.e. trajectory, laser, system calibration) to which influences of scanning geometry are added at the end of a flight line. The study of scanning geometry necessitates the classification of vegetation and coarse estimation of the terrain normal. This is achieved by a method that we formerly proposed for off-line quality analysis. The second part of the paper focuses on the positioning component. In high resolution scanning performed close to the terrain, the absolute accuracy of the resulting point cloud depends mainly on the quality of the trajectory which is related to the type of GPS solution (e.g. absolute positioning, DGPS, RTK). To reach sub-decimeter accuracy for the point cloud in the real-time, an RTK-GPS solution is needed. This requires the establishment of a communication link for the transmission of GPS corrections (or measurements). We analyze the usability of RTK-GPS/ALS acquired during several flights using different communication methods in the particular context of helicopter based missions. We focus mainly on the exploitation of nation-wide reference GNSS networks and confirm experimentally that the real-time registration of airborne laser data is feasible with sub-decimeter accuracy. Such quality is sufficient not only for a wide range of applications, but it also opens new opportunities for monitoring missions that require a short reaction time. Finally, we concentrate on situations when the phase and code corrections cannot be transmitted, and the quality of the differential carrier-phase positioning needs to be predicted. We validate the previously introduced indicators of positioning quality by simulated degradation of the input data.     

航空激光测深仪海面和海底激光入射点分布

依据卵形扫描系统的原理,以严格的数学推导为基础,推导了海平面激光入射点坐标的计算公式及相应的优化算法。建立起了海底激光入射点坐标及该点垂直水深的严密计算模型。通过仿真试验,得出了激光镜面反射点X轴的修正量随驱动电机转角的变化趋势,单个周期的海面激光入射点分布及30个周期的激光脉冲海面重叠图和试验脉冲对应的定位角度数据。同时给出了每个测量数据对应扫描镜中心点的位置和每个激光发射时对应XYZ坐标系中坐标原点的经纬度的计算方法。     

激光荧光雷达系统的测量方法与应用

本文叙述了应用激光荧光雷达系统测量海上溢油类别以及植被、岩矿、土壤、地被物等荧光光谱的方法与技术。该装置由N_2激光源、OSA光学光谱分析仪、卡斯格伦望远镜接收系统三部分组成。该装置可在室内,也可在室外25—60m远处测量各种物质的受激发射荧光。该仪器用标准灯谱进行了校正。     

Full-waveform topographic lidar: State-of-the-art

Airborne laser scanning (ALS) is an active remote sensing technique providing range data as 3D point clouds. This paper aims at presenting a survey of the literature related to such techniques, with emphasis on the new sensors called full-waveform lidar systems. Indeed, an emitted laser pulse interacts with complex natural and man-made objects leading to a temporal distortion of the returned energy profile. The new technology of full-waveform laser scanning systems permits one to digitize the complete waveform of each backscattered pulse. Full-waveform lidar data give more control to an end user in the interpretation process of the physical measurement and provide additional information about the structure and the physical backscattering characteristics of the illuminated surfaces. In this paper, the theoretical principles of full-waveform airborne laser scanning are first described. Afterwards, a review of the main sensors as well as signal processing techniques are presented. We then discuss the interpretation of full-waveform measures with special interest on vegetated and urban areas.     

以交叉累积剩余熵为准则的星载激光测高仪大光斑波形数据与地形匹配法

提出了一种基于交叉累积剩余熵的星载激光测高仪大光斑波形数据与地形匹配方法。根据星载激光测高仪大光斑回波波形信号包含地形结构信息的特性,将激光回波波形数据和数字表面模型(DSM)投影到统计特征空间,建立数据的统计特征向量,消除数据间维度差异,以交叉累积剩余熵为相似性测度匹配波形数据与地形的统计特征。试验结果表明,本方法能够较好地实现激光回波波形数据与地形的匹配,匹配精度达到一个像素以内。     

机载GPS、姿态和激光扫描测距集成定位系统的精确定位方程、误差分析与精度评估

全球定位系统（GPS），姿态测量（惯性导航系统（INS））和激光扫描测距技术集成的直接空对地定位系统是近年来遥感与测绘领域发展起来的新型定位技术，是定量化三维遥感中获取地面几何信息和生成数字高程模型的主要新技术手段之一。该文给出了该系统的精确定位方程，分析了误差源对定位精度的影响，并给出了数量级评估。结果对实际应用具有重要的参考价值。     

Quality Assessment Of Digital Surface Models Generated From IKONOS Imagery

The growing applications of digital surface models (DSMs) for object detection, segmentation and representation of terrestrial landscapes have provided impetus for further automation of 3D spatial information extraction processes. While new technologies such as lidar are available for almost instant DSM generation, the use of stereoscopic high-resolution satellite imagery (HRSI), coupled with image matching, affords cost-effective measurement of surface topography over large coverage areas. This investigation explores the potential of IKONOS Geo stereo imagery for producing DSMs using an alternative sensor orientation model, namely bias-corrected rational polynomial coefficients (RPCs), and a hybrid image-matching algorithm. To serve both as a reference surface and a basis for comparison, a lidar DSM was employed in the Hobart testfield, a region of differing terrain types and slope. In order to take topographic variation within the modelled surface into account, the lidar strip was divided into separate sub-areas representing differing land cover types. It is shown that over topographically diverse areas, heighting accuracy to better than 3 pixels can be readily achieved. Results improve markedly in feature-rich open and relatively flat terrain, with sub-pixel accuracy being achieved at check points surveyed using the global positioning system (GPS). This assessment demonstrates that the outlook for DSM generation from HRSI is very promising.     

机载激光扫描测高中激光脚点点群分割新方法

讨论了机载激光扫描测高激光脚点点群分割的方法,提出了一种新的分割成片房屋的激光脚点点群的方法———扫描带法,并给出了新方法的算法流程。实践表明,该算法运算速度快,分割准确、可靠。     

地面三维激光扫描地形测量数据粗差剔除算法及实现

本文基于地面三维激光扫描技术用于地形测量时点云数据的特点,得到引起结果存在粗差的障碍物上的点云具有坡度大于实际地形上坡度的特征,并据此提出了一种实用的粗差提取算法。对算法的原理、实现过程和其中重要参数的确定进行了分析,并编程实现了算法。最后,应用实例对粗差提取效果进行了检验,证明了算法的可行性和可靠性。     

距离门宽度对单光子激光测高卫星探测概率及测距精度的影响

针对距离门对单光子激光测高卫星探测概率以及测距精度的影响,结合激光雷达方程、单光子探测方程进行理论推导,采用不同宽度的距离门分析讨论,并利用蒙特卡洛方法进行模拟仿真试验。通过理论分析和仿真试验证明,距离门宽度对于探测概率影响不大,对于虚警概率具有较大影响,距离门为100 ns时,测距误差可以满足激光测高卫星的测距要求,当距离门宽度超过400 ns时,噪声占比会较大,测距精度会急剧下降,需要在数据后处理阶段采用精细化的滤波算法提取有效探测光子,保证测量精度。为保证对同一点重复观测25次,根据ICESat-2卫星的激光载荷参数,推导出光斑大小、光斑间距、激光重频三者之间的定量化关系。相关结论对于后续国产单光子激光测高卫星的设计与指标论证可提供一定参考。