The vertical mirror, its potential applications to theodolites and two star image stopping micrometers

A small area of a mirror can be made vertical with a high degree of accuracy by using a free mercury surface and an autocollimation target made of a mirror. The direction of the horizontal axis of a theodolite can be established, made and kept perpendicular to the vertical mirror for all telescope altitudes and the direction of the line of sight can be made, perpendicular to the horizontal axis with the same high degree of accuracy. Observations can thus be made on any part of a chosen celestial vertical circle much more accurately than by using the best striding levels. This application is potentially useful in determination of: astronomical longitude; changes in longitude differences with time, or the possible East-West component of continental drift; right ascension differences between stars; and the rotation rate of the Earth. Other applications include a leveling instrument of a new type, checking of tubular spirit levels, monitoring tidal variations in the direction of the plumb line, establishing an accurate 90° angle, and checking the graduations of the horizontal and vertical circles of theodolites. The impersonal micrometer for special astronomical observations stops the star image. Only parallel rays will enter the telescope when the observer is tracking the star keeping the star image stationary at the center of cross hairs.     

磁梯度张量系统的非线性集成矢量校正

磁梯度张量系统测量精度受到单磁传感器系统误差与传感器阵列间非对准误差的严重影响。为了获得精确的张量测量输出，建立了单磁传感器零漂、标度因子与非正交角等系统误差和多传感器轴系间非对准误差的集成数学模型，提出了基于十字磁梯度张量系统最小二乘非线性集成校正方法。相比两步标量校正，利用建立的集成数学模型能够一次性估计出十字形张量系统的48个误差参数，以"人造"平台输出为参考实现低成本矢量校正，极大提高了校正效率和参数估计准确率。仿真和实测表明，张量系统误差参数仿真估计准确率高于99.75%，实验校正后总场输出均方根误差（root mean square error，RMSE）小于2 nT，张量分量RMSE小于50 nT/m，参数估计具有较高的鲁棒性。     

高速滑轨控制测量网的建立及精度评估

针对火箭滑橇轨道准直度精密测量任务,该文分析了工程建设初期利用传统控制网布设方案存在的缺陷与不足,并提出了三级轨道控制网设计思想。首先选择高精度的一级控制网点,然后将控制网由原来的直线等距布设调整为面域均匀布设,最后将控制网布设方式由直线布设调整为东西对称布设,建立了高速轨道平面控制网的精度估算模型,分析了优化控制网的网点精度。结果表明:改进布网方式能够较好地实现对横、纵两个方向的精度控制。     

High-rate precise point positioning (PPP) to measure seismic wave motions: an experimental comparison of GPS PPP with inertial measurement units

High-rate GPS has been widely used to construct displacement waveforms and to invert for source parameters of earthquakes. Almost all works on internal and external evaluation of high-rate GPS accuracy are based on GPS relative positioning. We build an experimental platform to externally evaluate the accuracy of 50-Hz PPP displacement waveforms. Since the shake table allows motion in any of six degrees of freedom, we install an inertial measurement unit (IMU) to measure the attitude of the platform and transform the IMU displacements into the GPS coordinate system. The experimental results have shown that high-rate PPP can produce absolute horizontal displacement waveforms at the accuracy of 2–4 mm and absolute vertical displacement waveforms at the sub-centimeter level of accuracy within a short period of time. The significance of the experiments indicates that high-rate PPP is capable of detecting absolute seismic displacement waveforms at the same high accuracy as GPS relative positioning techniques, but requires no fixed datum station. We have also found a small scaling error of IMU and a small time offset of misalignment between high-rate PPP and IMU displacement waveforms by comparing the amplitudes of and cross-correlating both the displacement waveforms.     

基于地籍测量的惯性系统初始对准方法研究

地籍测量过程中具有静态、可调平和转位的特点,在静基座条件下,捷联惯性测量系统(SIMS)粗对准的失准角与卡尔曼滤波精对准的失准角相当,但是解析粗对准的方位角误差较大。本文在建立SIMS静基座粗对准误差方程的基础上,对影响解析粗对准精度的误差因素进行分析,提出利用光纤陀螺寻北仪进行四位置转位寻北的方法来估算方位角的精度,以提高方位角的估计精度。仿真结果表明,该方法可以有效地提高对准精度,适合于静基座外界干扰小的捷联式惯性测量系统上,在一定程度上可以直接作为对准的结果用于地籍测量定位解算。     

Geometric test field calibration of digital photogrammetric sensors

Test field system calibration will be a fundamental part of the future photogrammetric production line. Accurate calibration and performance evaluations are necessary for fully assessing the stability and accuracy of digital sensing techniques. In this paper, a method of comprehensive geometric calibration in a test field has been developed and empirically tested using eight image blocks collected with three UltraCamD digital large format photogrammetric cameras. Permanent photogrammetric test fields form the basis of the method. Important components of the method are determination of system parameters, evaluation of systematic errors, and assessment of geometric accuracy. The results showed that UltraCamD images contained systematic deformations that could not be modeled with single lens additional parameter models. Good point determination accuracy was obtained despite the systematic errors; the typical accuracy was 2–3 μm in image space in the horizontal coordinates and 0.05–0.09‰ of the object distance in height. One of the cameras had significantly poorer performance. In the worst cases, the horizontal accuracy was 5 μm in image space and the height accuracy was 0.18‰ of the object distance. The analog cameras gave better results than the UltraCamD, but the development of appropriate mathematical models for UltraCamD as well as improvements in digital sensors may change the situation in the near future.     

Inversion of a lidar waveform model for forest biophysical parameter estimation

Due to its measurement principle, light detection and ranging (lidar) is particularly suited to estimate the horizontal as well as vertical distribution of forest structure. Quantification and characterization of forest structure is important for the understanding of the forest ecosystem functioning and, moreover, will help to assess carbon sequestration within forests. The relationship between the signal recorded by a lidar system and the canopy structure of a forest can be accurately characterized by physically based radiative transfer models (RTMs). A three-dimensional RTM is capable of representing the complex forest canopy structure as well as the involved physical processes of the lidar pulse interactions with the vegetation. Consequently, the inversion of such an RTM presents a novel concept to retrieve biophysical forest parameters that exploits the full lidar signal and underlying physical processes. A synthetic dataset and data acquired in the Swiss National Park (SNP) successfully demonstrated the feasibility and the potential of RTM inversion to retrieve forest structure from large-footprint lidar waveform data. The SNP lidar data consist of waveforms generated from the aggregation of small-footprint lidar returns. Derived forest biophysical parameters, such as fractional cover, leaf area index, maximum tree height, and the vertical crown extension, were able to describe the horizontal and vertical forest canopy structure.     

国产机载大视场三线阵CCD相机GNSS偏心矢量和IMU视轴偏心角标定技术

针对国内首台自主研制的机载三线阵CCD相机（以下简称GFXJ）,开展了国产GFXJ的GNSS偏心矢量和IMU视轴偏心角标定技术研究工作。首先介绍了GFXJ相机的成像特点,然后分析建立了GFXJ的GNSS偏心矢量标定模型和IMU视轴偏心角标定模型,并提出了GNSS偏心矢量和视轴偏心角循环两步法标定方案,最后在国家嵩山遥感综合实验场获得了多次飞行试验数据。通过进行区域网平差和标定处理,验证了本文建立的GNSS偏心矢量标定模型和IMU视轴偏心角标定模型的正确性和有效性,证实了本文提出的循环两步法标定方案可靠、可行,可显著提升GFXJ的几何定位精度。利用GNSS偏心矢量和IMU视轴偏心角标定值,大幅提高了GFXJ相机的无控定位精度。辅以少量控制点进行区域网平差,GFXJ影像平面定位精度可满足1：1000地形图测图的空中三角测量精度要求,高程精度距离指标要求略有差距。目前该款相机仍在校飞阶段,定型后几何性能有望进一步提高。同时,本文建立的GNSS偏心矢量标定模型和IMU视轴偏心角标定模型及提出的循环两步法标定方案,可为其他机载线阵CCD相机的标定处理提供借鉴。     

轨道几何状态惯性检测系统零速姿态修正方法

为提高轨道几何状态惯性检测系统姿态精度,提出一种零速姿态修正方法,利用轨道几何状态惯性检测系统载体系横向及垂向速度为0的先验条件,构造Kalman滤波横向及垂向观测量。选用HT-50M型激光陀螺仪和JN-06A型石英挠性加速度计组成惯性导航系统,并进行现场检测试验。结果表明:在轨检仪连续工作300m情况下,零速姿态修正方法能够有效抑制惯性导航系统姿态误差增长,轨道检测精度提高2倍。     

基于小波降噪的IMU精对准性能分析

精对准性能是保障惯性导航精度必不可少的重要条件,论文总结了国内外精对准的研究现状,发现精对准一般是通过卡尔曼滤波和惯性传感器的小失准角线性误差方程实现;基于此,本文通过卡尔曼滤波及小波分析,对低、中、高三种不同性能的惯性传感器进行精对准性能分析,对比发现,高精度的惯性传感器有着较好的对准精度;而低精度的传感器,由于噪声偏差及非线性原因,对准精度较低,甚至出现滤波发散的情况.      

Accuracy assessment of lidar-derived digital elevation models

Despite the relatively high cost of airborne lidar-derived digital elevation models (DEMs), such products are usually presented without a satisfactory associated estimate of accuracy. For the most part, DEM accuracy estimates are typically provided by comparing lidar heights against a finite sample of check point coordinates from an independent source of higher accuracy, supposing a normal distribution of the derived height differences or errors. This paper proposes a new methodology to assess the vertical accuracy of lidar DEMs using confidence intervals constructed from a finite sample of errors computed at check points. A non-parametric approach has been tested where no particular error distribution is assumed, making the proposed methodology especially applicable to non-normal error distributions of the type usually found in DEMs derived from lidar. The performance of the proposed model was experimentally validated using Monte Carlo simulation on 18 vertical error data-sets. Fifteen of these data-sets were computed from original lidar data provided by the International Society for Photogrammetry and Remote Sensing Working Group III/3, using their respective filtered reference data as ground truth. The three remaining data-sets were provided by the Natural Environment Research Council's Airborne Research and Survey Facility lidar system, together with check points acquired using high precision kinematic GPS. The results proved promising, the proposed models reproducing the statistical behaviour of vertical errors of lidar using a favourable number of check points, even in the cases of data-sets with non-normally distributed residuals. This research can therefore be considered as a potentially important step towards improving the quality control of lidar-derived DEMs.     

轨道平顺性与测量精度

从轨道平顺性验收标准性切入，提出轨道平顺性对控制网的精度要求；指出轨道平顺性与控制点间的相对精度相关，与控制测量网垂直于线路的的横向误差及高程相关。     

卫星摄影测量中偏流角修正余差改正技术

本文基于立体影像摄影机理,对偏流角修正的剩余误差导致的上下视差进行了分析,建立了立体相机偏流角余差改正的数学模型,推导出偏流角余差影响上下视差的误差方程,并重点从相机参数在轨标定和光束法平差中低频误差补偿两方面提出解决措施。理论分析与实际卫星影像试验表明,偏流角改正余差对上下视差影响较大,必须通过相机参数在轨标定和低频误差补偿两方面予以改正,才能保证全球范围无地面控制点目标定位精度的一致性。     

利用高帧频相机检测运动控制轴精细形变

在运动控制应用场景中,由于疲劳等原因会导致设备微小形变,因此需要更加密集的观测手段与恢复方法.考虑到待检设备的摄影测量属性及高帧频相机高信息量特性,利用240帧/s的高帧频电荷耦合元件(charge coupled device,CCD)相机结合摄影测量方法实现对运动控制轴形变信息的精确量测,具体步骤如下:(1)固定标...     

基于自检校的机载线阵CCD传感器几何标定

将基于附加参数的自检校光束法区域网平差技术应用于机载线阵CCD传感器几何标定中,以ADS40为对象,分析集成传感器成像几何关系,引入GPS观测值数学模型和IMU视轴偏心角模型,建立用于标定的自检校光束法区域网平差模型;在深入分析机载三线阵CCD传感器成像误差特性的基础上,建立有效的相机标定参数模型;并采用检校场ADS40数据进行了标定试验,结果表明几何标定方法可行有效,可显著提高测量精度和可靠性。     

大失准角的SINS/GPS组合对准算法研究

利用四元数误差方程和非线性滤波技术能较好地解决大失准角下SINS的空中对准问题。迭代滤波比扩展卡尔曼滤波能在更大程度上改善对准精度，但计算量大。针对此不足，本文基于扩展卡尔曼滤波的状态与偏差解耦算法具有较高数值效率和迭代滤波具有较高精度的特点，推导出了一种非线性滤波算法，并对基于加性四元数误差方程的SINS／GPS组合对准进行了数字仿真。仿真结果表明：该算法既具有迭代滤波的精度又比迭代滤波计算量小。     

横-纵扫描的Voronoi图栅格生成算法

Voronoi图是计算几何学中一个重要数据结构,在诸多领域具有广泛的应用。栅格扫描算法符合计算机离散特征,优化了欧氏距离算法,是最优的栅格Voronoi图生成算法之一。但是,由于栅格单元距离与欧氏距离的差异,在扫描过程中部分单元的归属不可避免地产生一定的误差,使栅格Voronoi图的应用受到一定限制。本文针对传统扫描算法存在的误差缺陷,提出了一种基于横-纵扫描的栅格Voronoi图改进生成算法。首先,深入分析了传统扫描算法产生误差缺陷的原因和区域分布特征;然后,以3×3邻域为模板,在一个正常周期的水平(横向)扫描后,增加一个周期竖直(纵向)扫描,即通过横-纵两个周期扫描实现Voronoi图的准确生成;最后,应用不同的栅格数据进行了试验对比,结果表明:改进后的算法既具备扫描算法效率上的优势,同时解决了原算法扫描的误差缺陷,在高效生成的同时把误差限制在一个格网以内。     

Improving vertical GPS precision with a GPS-over-fiber architecture and real-time relative delay calibration

A limitation of GPS positioning is that the vertical component is generally two to three times less precise than the horizontal components. In a previous work by R. Santerre of Laval University and G. Beutler of University of Bern, it was shown in simulations that it is possible to improve the GPS vertical positioning precision by using a multi-antenna GPS receiver and a precise calibration technique of the relative hardware delay between the antennas and the receiver. However, no actual implementation of the system was done to prove the concept until now. A new multi-antenna, GPS-over-fiber architecture with real-time delay monitoring, designed and implemented to improve the vertical precision is presented. The improvement in vertical precision arises from the elimination of the relative receiver clock error in single difference, between antennas, and the precision real-time calibration of the relative hardware delay. Experiments were conducted with a zero baseline and a short baseline configuration. The results show, as expected by the theory and the simulations, a two to three times improvement in the precision of the vertical component such that it reached the same level of performance as the horizontal components. These promising results will enable the use of this type of configuration in several applications where the same precision in all 3D components is essential and could not be achieved before with standard GPS positioning techniques.     

北斗广域实时精密定位服务系统研究与评估分析

采用IGS、MGEX、北斗地基增强网的实时观测数据,研制北斗广域精密定位服务系统,实时生成北斗高精度轨道、钟差、电离层产品,提供厘米级北斗双频PPP、分米级单频PPP、米级单频伪距定位服务。对实时产品评估分析的结果表明:北斗卫星实时轨道与钟差产品URE统计精度约为2.0cm,实时电离层精度优于4.0TECU。采用全国分布的实时测站动态定位精度(95%置信度)评估分析表明:北斗双频PPP精度存在明显的区域特征,高纬度以及西部边缘地区的定位精度平面约0.2m,高程约0.3m;中部地区定位精度平面优于0.1m,高程优于0.2m,接近GPS实时PPP精度水平;北斗与GPS融合可以提高单北斗、单GPS的定位性能,尤其是显著加快了PPP收敛时间,收敛时间缩短到20min内。另外,除边缘地区外,北斗单频PPP实现平面0.5m,高程1.0m;北斗单频伪距单点定位实现平面2.0m,高程3.0m。     

利用激光雷达和多角度频谱成像仪数据估测森林垂直参数

植被的结构参数如植被高度、生物量、水平和垂直分布等，是影响陆地与大气能量交换乃至生物圈多样性的重要因素。多数遥感系统虽然可以提供植被水平结构的图像，但是不能提供植被成分垂直分布的信息。大尺度激光雷达仪器如LVIS产生的激光雷达信号，已成功地用于估计树高和森林生物量，然而大多数激光雷达仪器不具备图像能力，只能提供一个区域内的采样数据。其他的遥感数据如多角度高光谱、多频率多时相辐射计或雷达数据，可根据GLAS（Geoscience Laser Altimeter System）采样的测量用来推断出连续的森林结构区域覆盖参数。 MISR（Multi-angle Imaging Spectrometer）对陆表多角度的成像能力，可以通过BRDF的各向异性提供植被的结构信息。结合激光雷达的垂直采样和MISR的图像，区域内乃至全球性的森林空间参数的成像是可能的。ICESat卫星上的GLAS数据、Terra卫星上的MISR数据为区域或全球性森林结构参数提供了可能。本文的研究目的是评估GLAS数据，分析类似于MISR的数据对森林结构参数的估计能力。本文中使用了LVIS、AirMISR和GLAS数据。通过对GLAS树高的测量与GLAS像元内来自LVIS的平均树高对比，发现它们是高度相关的。同时还探讨了多角度频谱成像仪数据预测树高信息的能力，这将在今后区域内森林结构参数映射加以研究。