A weighted least squares solution for space intersection ofspaceborne stereo SAR data

The use of stereoscopic SAR images offers an alternative to interferometric SAR for the generation of digital elevation models (DEMs). The stereo radargrammetric method is robust and can generate DEMs of sufficient accuracy to geocode SAR images. Previous work has shown that ground coordinates with accuracy of four times the resolution cell can be obtained from ERS data without using any ground control points (GCPs), where the high accuracy of the orbit and satellite position of the order of metres introduce insignificant errors into the intersection procedure. The orbit data for RADARSAT is not as accurate as that for ERS, and the perpendicular relationship between the resultant velocity vector and the resultant range vector is uncertain in terms of image geometry. Hence, it is necessary to refine the method to allow for possible errors. This paper introduces a weighted space intersection algorithm based on an analysis of the predicted errors. A radargrammetric error model for observation errors is also formulated to predict the accuracy of the algorithm. The revised method can be used without any GCPs, but this can lead to systematic errors due to less accurate orbit data, and it has been found that the use of two GCPs provides a reasonable solution. The method is insensitive to the spatial distribution of GCPs, which is often critical in traditional methods. The error statistics of the results generated from 32 independent check points, distributed through the entire SAR image, approach the predicted errors and give positional accuracy of 38 m in three dimensions     

GPS‐Based Orbit Determination for KOMPSAT‐5 Satellite

Korea Multi‐Purpose Satellite‐5 (KOMPSAT‐5) is the first satellite in Korea that provides 1 m resolution synthetic aperture radar (SAR) images. Precise orbit determination (POD) using a dual‐frequency IGOR receiver data is performed to conduct high‐resolution SAR images. We suggest orbit determination strategies based on a differential GPS technique. Double‐differenced phase observations are sampled every 30 seconds. A dynamic model approach using an estimation of general empirical acceleration every 6 minutes through a batch least‐squares estimator is applied. The orbit accuracy is validated using real data from GRACE and KOMPSAT‐2 as well as simulated KOMPSAT‐5 data. The POD results using GRACE satellite are adjusted through satellite laser ranging data and compared with publicly available reference orbit data. Operational orbit determination satisfies 5 m root sum square (RSS) in one sigma, and POD meets the orbit accuracy requirements of less than 20 cm and 0.003 cm/s RSS in position and velocity, respectively.     

利用单个地面控制点的SAR 图像高精度立体定位

几何构像模型和定向参数解算方案的选择是实现SAR 图像高精度立体定位的关键。该文针对稀少控制下斜侧视SAR 图像高精度定位难题,设计了利用单个地面控制点的SAR 图像立体定位方案。该方案利用轨道参数获取成像瞬间天线相位中心的位置、速度,并利用一个地面控制点标定近距延迟和多普勒中心频率,实现定向参数的精确解算和SAR 图像的高精度立体定位。采用中国测绘科学研究院获取的机载SAR 图像进行了立体定位实验,统计分析了其定位误差,验证了该文方法的精确性和有效性。      

Orbit Determination Accuracy Improvement for Geostationary Satellite with Single Station Antenna Tracking Data

An operational orbit determination (OD) and prediction system for the geostationary Communication, Ocean, and Meteorological Satellite (COMS) mission requires accurate satellite positioning knowledge to accomplish image navigation registration on the ground. Ranging and tracking data from a single ground station is used for COMS OD in normal operation. However, the orbital longitude of the COMS is so close to that of satellite tracking sites that geometric singularity affects observability. A method to solve the azimuth bias of a single station in singularity is to periodically apply an estimated azimuth bias using the ranging and tracking data of two stations. Velocity increments of a wheel offloading maneuver which is performed twice a day are fixed by planned values without considering maneuver efficiency during OD. Using only single‐station data with the correction of the azimuth bias, OD can achieve three‐sigma position accuracy on the order of 1.5 km root‐sum‐square.     

Accurate geometric correction of ATSR images

An accurate geometric correction algorithm of raw ATSR images is proposed in this paper. The proposed algorithm is divided into two modules: pre-correction and precision correction. In the pre-correction algorithm, the scanning geometry of the ATSR, ephemeris data and the Earth's shape and rotation were modeled mathematically. It corrected elliptically-distorted raw ATSR images and resulted in a mean collocation error of 1 pixel between the nadir and forward images. The proposed navigation model showed a better geolocation performance than ATSR image geometric correction algorithms currently in operation. The geometric errors in the pre-corrected images were reduced further by the precision correction algorithm. Coastlines were detected from the pre-corrected nadir and forward images and matched with map coastline data. The matched coastline pixels, GCPs, were combined with the pre-correction model to estimate the errors of the position, velocity and attitude of the satellite. An extended Kalman filter was used for the optimal estimation. The corrected images showed the collocation error of 0.4 pixel and the geolocation error of 0.7 pixel. The results were compared with those from a polynomial warping technique. It proved that the proposed precision correction algorithm gave better geometric correction performance than collocation algorithms based on a polynomial warping technique     

多策略ATLAS数据优选与影像匹配相结合的SAR高程控制点提取

为了精化星载SAR影像几何参数并提高立体定位精度,借鉴星载激光测高数据光学遥感影像高程控制点提取思路,设计了一种多策略高级地形激光测高系统(ATLAS)数据优选与影像匹配相结合的SAR高程控制点提取方法。该方法采用非夜间观测光子滤除、高置信度光子选取、SRTM DEM辅助的粗差剔除、大偏心率椭圆滤波核平坦区域光子筛选等多种策略,从ATLAS数据ATL03级产品中提取高质量、平坦区域的激光高程点,再依据SRTM DEM对斜距SAR影像进行地理编码,按激光高程点的平面坐标选取局部谷歌地球影像作为足印影像,采用秩自相似描述子进行足印影像与SAR地理编码影像的匹配,得到与激光高程点对应的SAR影像像点坐标,从而提取SAR高程控制点。采用中国登封市、日本横须贺市两个区域的ATLAS数据进行了高分三号SAR高程控制点提取实验,利用提取的高程控制点进行SAR影像几何参数精化,大幅提升了立体定位精度,验证了该文高程控制点提取方法的可行性和有效性。      

MOS and SEASAT image geometric corrections

Results of studies to generate precise orthoimages from MOS-MESSR data in the visible spectral range and SEASAT-SAR data in the microwave range are reported. The raw MOS-MESSR image has four spectral bands, with an interband misregistration of three to four pixels. A methodology for orthoimage generation directly from each band of the raw image is described. For thematic applications with SEASAT images, most users have access only to slant range or ground range image products, which are often not georeferenced or geocoded with a standardized pixel spacing. The same methodology for creating orthoimages has been adapted for spaceborne SAR images, and tested with a ground range SEASAT image. The analysis of the sensor and satellite motion geometries and the use of a photogrammetric approach allows a rigorous mathematical model for the geometric correction and the rectification of the raw images to be derived. The final accuracy of the geometric corrections is about 25 m for both data types, using only six ground control points     

GPS卫星精密星历插值在靶场数据处理中的比较

为了提高目标在地心坐标系的绝对定位精度,降低星历误差对单点定位和相对定位的影响,必须采用GPS卫星的精密星历。精密星历在GPS数据处理时需构造合适的插值模型进行内插,才能得到任意时刻卫星的位置。分析比较了2种经典的多项式插值及逐次线性插值的Neville算法的数学模型及插值结果,探讨了3种插值算法的适用范围,得到了适用于靶场精密星历的处理的插值方法。     

Turning images into 3-D models

In this article developments and performance analysis of image matching for detailed surface reconstruction of heritage objects is discussed. Three dimensional image-based modeling of heritages is a very interesting topic with many possible applications. In this article we propose a multistage image-based modeling approach that requires only a limited amount of human interactivity and is capable of capturing the fine geometric details with similar accuracy as close-range active range sensors. It can also cope with wide baselines using several advancements over standard stereo matching techniques. Our approach is sequential, starting from a sparse basic segmented model created with a small number of interactively measured points. This model, specifically the equation of each surface, is then used as a guide to automatically add the fine details. The following three techniques are used, each where best suited, to retrieve the details: 1) for regularly shaped patches such as planes, cylinders, or quadrics, we apply a fast relative stereo matching technique. 2) For more complex or irregular segments with unknown shape, we use a global multi-image geometrically constrained technique. 3) For segments unsuited for stereo matching, we employ depth from shading (DFS). The goal is not the development of a fully automated procedure for 3D object reconstruction from image data or a sparse stereo approach, but we aim at the digital reconstruction of detailed and accurate surfaces from calibrated and oriented images for practical daily documentation and digital conservation of wide variety of heritage objects.     

一种基于图像分割的动态规划立体匹配算法

本文提出了一种基于图像分割的动态规划立体匹配算法。此算法首先利用MeanShift图像分割算法对左右图像对进行分割处理,从而得到分割域的深度范围约束;然后结合窗口匹配及可信度约束得到地面控制点;综合地面控制点和其所属分割域的深度一致性关系可以有效剔除部分不可信点;以地面控制点和分割域作为约束信息,对动态规划的数据能量项和遮挡能量项加入分割域关系约束,利用动态规划算法得到最终视差图。实验结果表明,该算法可得到较好的视差结果。     

Simple stereo algorithm for 3D positioning of object points

A simple stereo algorithm for 3D positioning of object points is presented. The superimposed difference image is formed from a pair of stereo images. The features are extracted from only the superimposed difference image and the disparity is determined by searching paired features in the given window without recourse to the stereo matching     

Geometric integration of NOAA AVHRR and SPOT data: low resolutioneffective parameters from high resolution data

Information available from ephemeris data, combined with a few ground control points, is used to carry out the geometric combination of NOAA, AVHRR, and SPOT images by means of orbital models for each satellite. The observation conditions are reconstructed and the areas observed in common determined in the SPOT image pixels and each low-resolution AVHRR pixel. The determination of effective parameters, at low spatial resolution, from high-spatial-resolution data takes into account overlapping effects between adjacent pixels, and pixel size and shape variations with viewing angle for AVHRR data. The method is applied to surface temperature mapping of a selected heterogeneous area by incorporating NOAA AVHRR thermal data in a high-spatial-resolution emissivity map derived from SPOT data     

Precise Geometric Registration of Aerial Imagery and LIDAR Data

In this paper, we develop a registration method to eliminate the geometric inconsistency between the stereo‐images and light detection and ranging (LIDAR) data obtained by an airborne multisensor system. This method consists of three steps: registration primitive extraction, correspondence establishment, and exterior orientation parameter (EOP) adjustment. As the primitives, we employ object points and linked edges from the stereo‐images and planar patches and intersection edges from the LIDAR data. After extracting these primitives, we establish the correspondence between them, being classified into vertical and horizontal groups. These corresponding pairs are simultaneously incorporated as stochastic constraints into aerial triangulation based on the bundle block adjustment. Finally, the EOPs of the images are adjusted to minimize the inconsistency. The results from the application of our method to real data demonstrate that the inconsistency between both data sets is significantly reduced from the range of 0.5 m to 2 m to less than 0.05 m. Hence, the results show that the proposed method is useful for the data fusion of aerial images and LIDAR data.     

DEM generation by means of ERS tandem data

This paper presents an application of the European Remote Sensing (ERS) satellites' radar data to digital elevation model (DEM) generation. The selected test site is the Sannio-Matese area in southern Italy, where several corner reflectors (CRs) were deployed to be used as ground control points (GCPs) for height measurement accuracy validation. First of all, an analysis of the CR response in radar images is presented. Then, the procedure for image pair geometric registration and interferogram formation is described in detail. A quantitative analysis is also performed by comparing these interferograms to the corresponding products obtained by using the ISAR software, officially distributed by the European Space Agency (ESA). Reported correlation values show that only tandem pairs allow an efficient interferometric processing to be performed, thanks to their short-time baseline (one day), whereas correlation adequate for differential interferometry could not be achieved. The method adopted for the computation of the interferometric baseline components on the basis of satellite orbital data is described, including the GCP-based corrections. The procedure was applied to obtain DEMs of a 10×10 km² subarea characterized by very high correlation coefficients (0.6). The best attained values of the GCP height measurement accuracy were about 4 m. Finally, the DEMs were compared, giving root mean square (rms) differences less than 20 m in the best case     

基于空变多项式的高精度重构模型

针对由于合成孔径雷达(SAR)图像几何失真的空变性,传统的多项式模型与距离多普勒模型精度不高的问题,文中提出了结合距离多普勒模型和空变的多项式模型的少量控制点精确重构模型。该模型从距离多普勒方程出发,通过优化地面控制点的方位向分布建立空变的多项式模型,实现SAR图像的高精度重构。实验数据表明:在少量控制点情况下,文中的重构模型精度高于传统的距离多普勒模型和多项式模型。     

一种新的稀少控制条件下机载SAR影像区域网平差方法的研究

困难测图地区缺少控制点一直是SAR图像校正的难点之一。该文针对机载SAR影像,提出了一种新的基于F.leberl构像模型平差的方法。借鉴光束法平差方法中解算前、后方交会的思想,交替趋近求解未知参量。实验结果表明,该方法不仅实现了在稀少控制点下求得定位参数的稳定解,而且有效减小了航带间同名点坐标误差,平差精度达到了单航带多控制点独立校正的水平。     

基于光线追迹的长线列摆扫式热像仪在轨几何成像仿真方法

针对卫星发射前在轨数据缺乏导致的无法进行成像质量评估、链路分析及几何处理算法验证等问题,提出了一种基于光线追迹的长线列摆扫式热像仪在轨几何成像仿真方法.首先根据光学系统结构及成像特点,构建了长线列摆扫式热像仪严格几何定位模型;然后,基于姿轨仿真数据、DOM和DEM辅助数据,通过光线追迹及重投影算法实现了像元视矢量的空间...     

卫星干扰源精确定位的位置校正算法

卫星干扰源定位系统可以通过测量两颗卫星对干扰源形成的时差(DTO)和频差(DFO)来完成对未知干扰源的定位,但卫星的星历难以准确测定,其微小变化将引起定位结果的较大误差.针对这一问题,提出利用多个位置校正站来修正卫星星历以消除其对定位结果影响的算法,并通过理论推导证明了有四个或四个以上的位置校正站时,该算法可以消除卫星星历不准确对定位结果的影响.仿真结果表明,与未采用位置校正站的定位结果相比,该算法能获得优于一个数量级以上的定位精度改善.     

无控制点条件下的PHI影像几何校正

利用空间位置测量系统对因遥感平台不稳定而引起的影像畸变进行校正是目前航空摄影测量常用的方法.介绍了对推帚成像模式在无地面控制点情况下采集的影像进行几何校正的原理和方法,即利用POS数据解算外方位元素并建立共线方程,从而实现影像的几何校正.用PHI航空遥感影像进行了实验.实验表明,在无地面控制点的情况下,利用POS数据辅...     

Highly Dense 3D Surface Generation Using Multi‐image Matching

This study presents an automatic matching method for generating a dense, accurate, and discontinuity‐preserved digital surface model (DSM) using multiple images acquired by an aerial digital frame camera. The proposed method consists of two main procedures: area‐based multi‐image matching (AMIM) and stereo‐pair epipolar line matching (SELM). AMIM evaluates the sum of the normalized cross correlation of corresponding image points from multiple images to determine the optimal height of an object point. A novel method is introduced for determining the search height range and incremental height, which are necessary for the vertical line locus used in the AMIM. This procedure also includes the means to select the best reference and target images for each strip so that multi‐image matching can resolve the common problem over occlusion areas. The SELM extracts densely positioned distinct points along epipolar lines from the multiple images and generates a discontinuity‐preserved DSM using geometric and radiometric constraints. The matched points derived by the AMIM are used as anchor points between overlapped images to find conjugate distinct points using epipolar geometry. The performance of the proposed method was evaluated for several different test areas, including urban areas.