A simple and feasible orientation method for the three-line cameras of the ZiYuan-3 (ZY-3) satellite is introduced. The method calibrates the CCD-detector look angles in the attitude determination reference (ADR) coordinate system rather than modifying the laboratory-calibrated orientation parameters, which are not necessary for the geometric calibration. Additionally, the unknown parameters of the model are virtually uncorrelated. Experimental results show that the direct georeferencing accuracy of ZY-3 nadir images have been improved from the kilometre level to better than 9 m in planimetry, and that of the forward-and-backward stereopair was also raised to better than 18 m in plan and 4 m in height. After a bundle adjustment using four ground control points, a higher accuracy of about 3·4 m in plan and 1·6 m in height was achieved.

Resume

Cet article presente une methode simple a mettre en oeuvre pour l'orientation des cameras a trois barrettes du satellite ZiYuan-3 (ZY-3). La methode consiste a etalonner les angles de visee des detecteurs CCD dans le repere de determination d'attitude au lieu de modifier les parametres d'orientation determines en laboratoire, qui ne sont pas necessaires pour l’etalonnage geometrique. En outre, les inconnues du modele sont virtuellement decorrelees. Les resultats experimentaux montrent que la precision de georeferencement direct des images ZY-3 prises en visee verticale est amelioree d'un ordre de grandeur kilometrique a mieux que 9 m en planimetrie, et que celle des couples stereoscopiques avant-arriere atteint mieux que 18 m en planimetrie et 4 m en altimetrie. Apres une compensation par faisceaux utilisant quatre points d'appui, la precision est encore amelioree et atteint 3,4 m en planimetrie et 1,6 m en altimetrie.

Zusammenfassung

Dieser Beitrag stellt eine einfache und praktikable Orientierungsmethode fur die Dreizeilenkameras des ZiYuan-3 (ZY-3) Satelliten vor. Diese Methode kalibriert die Aufnahmerichtungen der CCD-Detektoren in dem Referenzkoordinatensystem (ADR) der Neigungsbestimmung, anstatt die Parameter der Laborkalibrierung zu modifizieren, die fur die geometrische Kalibrierung nicht notwendig sind. Zusatzlich sind die unbekannten Parameter des Models praktisch unkorreliert. Experimentelle Ergebnisse zeigen, dass die Genauigkeit der direkten Georeferenzierung der Nadirbilder des ZY-3 Satelliten sich vom km Niveau auf besser als 9 m in der Lage gesteigert hat, und die Genauigkeit des Stereopaares aus vorwarts und ruckwarts Blick sich auf unter 18 m in der Lage und 4 m in der Hohe verbessert hat. Nach einer Bundelausgleichung mit vier Passpunkten konnte eine noch hohere Genauigkeit von ca. 3·4 m in der Lage und 1·6 m in der Hohe erzielt werden.

Resumen

Se introduce un metodo simple y asequible de orientacion para el satelite tri-linear ZiYuan-3 (ZY-3). El metodo calibra los angulos de apuntamiento de los detectores CCD en el sistema de referencia de actitud (ADR) en lugar de modificar los parametros de orientacion medidos en laboratorio, los cuales no son necesarios para la calibracion geometrica del satelite. Ademas, los parametros desconocidos del modelo estan practicamente libres de correlacion. Los resultados experimentales demuestran que la precision de la georeferenciacion directa de las imagenes del nadir del ZY-3 han mejorado de nivel kilometrico a niveles mejores que 9 m en planimetria, y que en el caso estereo de los puntos de vista anterior i posterior tambien ha alcanzado niveles mejores que los 18 m en planimetria y 4 m en altimetria. Una vez realizado un ajuste de haces con cuatro puntos de control, se alcanzan precisiones mayores: 3·4 m en planimetria y 1·6 m en altimetria.

摘 要

提出了一种简单 、可行的资源三号卫星三线阵相机几何定位方法。该方法在姿态测量参考坐标系下对CCD探元指向角进行几何检校,而无需重新计算实验室检校获得的定位参数。而且,在几何检校过程中,实验室检校参数并非必需的,检校模型的未知数之间也不存在相关性。实验结果表明,资源三号下视影像直接定位的平面精度由公里级提高到了优于9米,前后视立体像对的平面与高程定位精度也分别提高到了优于18米和4米。利用4个地面控制点进行光束法平差后,可获得的平面精度约3·4米、高程精度约1·6米。

In-orbit geometric calibration and validation of ZY-3 three-line cameras based on CCD-detector look angles

The automatic extraction of terrain from high-resolution satellite optical images is very difficult under cloudy conditions. Therefore, accurate cloud detection is necessary to fully use the cloud-free parts of images for terrain extraction. This paper addresses automated cloud detection by introducing an image matching based method under a stereo vision framework, and the optimization usage of non-cloudy areas in stereo matching and the generation of digital surface models (DSMs). Given that clouds are often separated from the terrain surface, cloudy areas are extracted by integrating dense matching DSM, worldwide digital elevation model (DEM) (i.e., shuttle radar topography mission (SRTM)) and gray information from the images. This process consists of the following steps: an image based DSM is firstly generated through a multiple primitive multi-image matcher. Once it is aligned with the reference DEM based on common features, places with significant height differences between the DSM and the DEM will suggest the potential cloud covers. Detecting cloud at these places in the images then enables precise cloud delineation. In the final step, elevations of the reference DEM within the cloud covers are assigned to the corresponding region of the DSM to generate a cloud-free DEM. The proposed approach is evaluated with the panchromatic images of the Tianhui satellite and has been successfully used in its daily operation. The cloud detection accuracy for images without snow is as high as 95%. Experimental results demonstrate that the proposed method can significantly improve the usage of the cloudy panchromatic satellite images for terrain extraction.

Automatic cloud detection for high resolution satellite stereo images and its application in terrain extraction

ZY-3 is the first Chinese civilian high-resolution stereo-mapping satellite, designed for 1:50 000 scale mapping. Although ZY-3 has a very high accuracy for direct image geolocation without ground control points (GCPs), the use of some GCPs is still indispensable for stereo mapping. A novel method is proposed whereby spaceborne Geoscience Laser Altimeter System (GLAS) laser altimetry datasets are viewed as generalised height control points to support a ZY-3 block adjustment. This method separates planimetric and height control, integrating the latter with GLAS data such that, without other GCPs, the vertical accuracy of ZY-3 images can be improved significantly. Both flat and mountainous terrain were selected to evaluate the proposed method. The results show that by adding two GLAS height control points for a single image, or spaced every 50 km in the along-track (orbital) direction for block images, the vertical accuracy can satisfy the requirements of 1:50 000 scale mapping, thus reducing the need for field surveying. Additionally, the method will be valuable for integrating spaceborne laser altimetry data and optical images for global mapping without any GCPs.

Resume

ZY-3 est le premier satellite civil chinois pour la cartographie stereoscopique a haute resolution, concu pour la cartographie a l'echelle 1:50 000. Malgre la grande precision intrinseque de ZY-3 pour la localisation directe des images sans points d'appui, le recours a quelques points d'appui reste indispensable pour la cartographie stereoscopique. Cet article propose une nouvelle methode qui utilise les donnees du lidar spatial GLAS (Geoscience Laser Altimeter System) comme des points d'appui altimetriques generalises pour le recalage de blocs ZY-3. Cette methode separe les recalages planimetrique et altimetrique, et utilise pour ce dernier les donnees GLAS afin d'ameliorer significativement la precision altimetrique des images ZY-3 sans aucun autre point d'appui. Des sites ont ete selectionnes a la fois dans des regions de plaine et de montagne pour evaluer la methode proposee. Les resultats montrent qu'en introduisant deux points d'appui altimetriques issus de GLAS dans une meme image, ou des points espaces de 50 km dans la direction de l'orbite pour des blocs d'images, la precision verticale devient conforme aux exigences de la cartographie au 1:50 000 ce qui permet de reduire les operations de terrain. Ainsi, cette methode permettra d'integrer des donnees lidar spatiales et des images optiques pour une cartographie globale sans aucun point d'appui.

Zusammenfassung

ZY-3 ist der erste zivile chinesische hochauflosende Stereosatellit, der fur Kartierung im Masstab 1:50 000 entwickelt wurde. Obwohl ZY-3 eine sehr hohe Genauigkeit fur die direkte Bildorientierung ohne Passpunkte (GCPs) besitzt, ist der Einsatz von einigen Passpunkten fur die Stereokartierung unerlasslich. Deshalb wird eine neuartige Methode vorgestellt, fur die Laserhohendatensatze des satellitengestutzten Geoscience Laser Altimeter Systems (GLAS) als generalisierte Hohenpasspunkte die ZY-3 Bundelausgleichung unterstutzen. Bei dieser Methode werden planimetrische und Hohenkontrolle getrennt, wobei letztere mit GLAS-Daten gestutzt wird, so dass ohne weitere Passpunkte die Hohengenauigkeit der ZY-3 Bilder signifikant gesteigert werden kann. Es wurden Gebiete mit flachem und gebirgigem Gelande zur Evaluation der neuen Methode ausgewahlt. Die Ergebnisse zeigen, dass fur ein Einzelbild durch Einfuhrung von zwei zusatzlichen GLAS Hohenpasspunkten, bzw. bei einem Block von Bildern durch im Abstand von je 50 km entlang der Satellitenbahn gewahlten GLAS Hohenpasspunkten die erzielte Hohengenauigkeit fur die Anforderungen einer Kartierung im Masstab 1:50 000 ausreichend ist. Damit kann der Bedarf an Vermessung im Feld reduziert werden. Zusatzlich ist die Methode fur die Integration von satellitengestutzten Laserhohenmessdaten und optischen Bilddaten fur eine globale Kartierung ohne Passpunkte von Vorteil.

Resumen

ZY-3 es el primer satelite cartografico civil chino con capacidad estereo de alta resolucion, disenado para derivar cartografia a escala 1:50 000. A pesar de la alta precision del ZY-3 en la geolocalizacion directa de imagen sin puntos de control en tierra (GCP), sigue siendo necesario el uso de algunos GCP en el uso estereoscopico de las imagenes. Se propone un nuevo metodo en el que los conjuntos de datos captados con Geoscience Laser Altimeter System (GLAS) se usan como puntos de control vertical en un ajuste de imagenes ZY-3. En este metodo se separa el control horizontal del vertical, integrando estos ultimos a los datos GLAS mejorando significativamente la precision vertical de las imagenes ZY-3 sin anadir GCP. El metodo propuesto se ha evaluado tanto en terreno llano como montanoso. Los resultados muestran que mediante la inclusion de dos puntos de control verticales GLAS para una sola imagen, o puntos espaciados cada 50 km a lo largo de la trayectoria (orbital) de las imagenes del bloque, la precision vertical puede satisfacer los requisitos de la cartografia a escala 1:50 000, reduciendose la necesidad de trabajos topograficos de campo. Ademas, el metodo sera de gran valor para la integracion de datos de altimetria laser bordo de vehiculos espaciales e imagenes opticas para la cartografia global sin GCP.

摘要

资源三号是中国的第一颗高分辨率民用立体测图卫星,主要用于1:50 000比例尺测图。虽然资源三号有比较高的无控定位精度,但在高精度测图时仍然需要一定数量的地面控制点。文章提出了一种利用ICESat卫星上的地学激光测高仪GLAS数据作为高程控制辅助资源三号区域网平差的新方法。试验表明,该方法能在没有其他地面控制点的情况下,显著提升资源三号的无控高程精度。对于单景影像,在沿轨方向加入两个GLAS高程控制点,对于大区域影像,沿轨间隔50 km左右选择GLAS高程控制点,能达到1:50 000测图的高程要求。该方法对于未来采用星载激光测高数据与光学立体影像集成用于全球无控立体测图具有一定的参考价值。

ZY‐3 Block adjustment supported by glas laser altimetry data

Nadir viewing satellite image is an effective data source to generate orthomosaics. Because of the georeferencing error of satellite images, block adjustment is the first step of orthomosaic generation over a large area. However, the geometric relationship of the neighboring orbits of the nadir viewing images is not rigid enough. This paper proposes a new rational function model (RFM) block adjustment approach that constrains the tie point elevation to enhance the relative geometric rigidity. By interpolating the elevations of tie points in a digital elevation model (DEM) and estimating the a priori errors of the interpolated elevations, better overall relative accuracy is obtained, and the local optimal solution problem is avoided. By constraining the adjusted model parameters according to the a priori error of RFMs, block adjustment without ground control point (GCP) is performed. By optimal initializing the object–space positions of tie points with multi-backprojection method, the needed iteration times of block adjustment are reduced. The proposed approach is investigated with 46 Ziyuan-3 sensor-corrected images, a 1:50 000 scale DEM, and 586 GCPs. Compared with Teo's approach that constrains the horizontal coordinates and elevations of tie points, the approach in this paper converges much faster when the GCPs are sparse, and meanwhile, the absolute and relative accuracy of the two approaches are almost the same. The result of block adjustment with only four GCPs shows that no accuracy degeneration occurred in the test area and the root-mean-square error of independent check point reaches about 1.5 ground resolutions. Different DEMs and number of tie points are used to investigate whether the block adjustment result is influenced by these factors. The results show that better DEM accuracy and denser tie points do improve the accuracy when the images have large side-sway angles. The proposed approach is also tested with 5118 IKONOS-2 images that cover the southern Europe without GCP. The result shows that the relative mosaicking accuracy is much better than that of Grodecki's approach.

DEM-Assisted RFM Block Adjustment of Pushbroom Nadir Viewing HRS Imagery

This paper presents a novel image matching method for multi-source satellite images, which integrates global Shuttle Radar Topography Mission (SRTM) data and image segmentation to achieve robust and numerous correspondences. This method first generates the epipolar lines as a geometric constraint assisted by global SRTM data, after which the seed points are selected and matched. To produce more reliable matching results, a region segmentation-based matching propagation is proposed in this paper, whereby the region segmentations are extracted by image segmentation and are considered to be a spatial constraint. Moreover, a similarity measure integrating Distance, Angle and Normalized Cross-Correlation (DANCC), which considers geometric similarity and radiometric similarity, is introduced to find the optimal correspondences. Experiments using typical satellite images acquired from Resources Satellite-3 (ZY-3), Mapping Satellite-1, SPOT-5 and Google Earth demonstrated that the proposed method is able to produce reliable and accurate matching results.

An Image Matching Algorithm Integrating Global SRTM and Image Segmentation for Multi-Source Satellite Imagery

The advantages of continuously and soundly obtaining large multidimensional, multiscale and multitemporal observation datasets from satellite remote sensing make it indispensable in building a national spatial data infrastructure. This paper introduces the ZY-3 satellite developed in China and discusses a fully automatic data-processing system to generate geoinformation products, such as digital elevation models (DEMs) and digital orthophotomaps (DOMs), based on ZY-3 imagery. The key technologies of automatic geoinformation product generation, including strip image-based bundle adjustment together with creating DEMs and DOMs, are illustrated. The accuracies of the georeferencing and automatically generated geoinformation products are also discussed. This automatic dataprocessing system is shown to provide a good foundation for near real-time derivation of such geoinformation products and for the promotion and application of Chinese domestic satellites.

Fully automatic generation of geoinformation products with chinese zy-3 satellite imagery

A method for automatically estimating the transformation parameters between road centre-line vector maps and high resolution satellite images is proposed. The advantages of the method are that global image feature extraction is avoided and feature extraction and matching are achieved simultaneously by using the vector data as guidance. The road width, as estimated by the algorithm, together with the road direction are used as constraints to refine the matching results. Arbitrarily chosen road nodes contribute to improving the adjustment. Map-to-image matching has advantages over image-to-image matching and could be a good method for the rapid updating of geographical information system (GIS) data.

Resume

Une methode est proposee pour estimer automatiquement les parametres de transformation entre des cartes routieres en mode vecteur et des images satellitales a haute resolution. Les avantages de cette methode sont qu'elle n'a pas besoin d'extraction globale d'objets dans les images, et que l'extraction et l'appariement se font simultanement en s'appuyant sur les donnees vectorielles. La largeur des routes, qui est estimee par l'algorithme, ainsi que leur direction, sont utilisees comme contraintes pour affiner les resultats de l'appariement. Des nœuds routiers choisis arbitrairement contribuent a ameliorer le recalage. Le recalage de la carte sur l'image presente des avantages par rapport au recalage entre images, et pourrait etre un moyen approprie pour une mise a jour rapide des donnees dans les systemes d'information geographique.

Zusammenfassung

Dieser Beitrag stellt eine Methode zur automatischen Bestimmung der Transformationsparameter zwischen Strasenachsen aus vektoriellen Kartendaten und hochauflosenden Satellitenbilddaten vor. Merkmalsextraktion und -zuordnung werden, gesteuert durch die Vektordaten, simultan gelost. Strasenbreite und -richtung werden durch den Algorithmus bestimmt und dienen als Bedingungen, um die Zuordnungsergebnisse zu verbessern. Beliebige Strasenkreuzungen konnen fur die Ausgleichung unterstutzend wirken. Die Zuordnung von Karte zu Bild hat Vorteile gegenuber einer Bild zu Bildzuordnung und konnte somit fur eine zugige Fortfuhrung von GIS Daten vorteilhaft sein.

Resumen

Se propone un metodo para estimar de forma automatica la transformacion entre la linea central de carretera en mapas vectoriales e imagenes de satelite de alta resolucion. Las ventajas del metodo son que se evita la extraccion global de caracteristicas de la imagen y la extraccion de caracteristicas y su correspondencia se realizan simultaneamente usando el mapa vectorial como guia. El ancho de la via, estimada por el algoritmo, conjuntamente con la direccion de la carretera son usados como restricciones para refinar el resultado de la correspondencia. Los nodos arbitrarios de la carretera contribuyen a mejorar el ajuste. La correspondencia mapa a imagen tiene ventajas frente a la correspondencia imagen a imagen y puede ser un buen metodo para la actualizacion rapida de datos SIG.

Estimation of Transformation Parameters Between Centre‐Line Vector Road Maps and High Resolution Satellite Images

Three key techniques in registration of CBERS-02B image are introduced in this paper. Including an improved image
matching strategy aided by a voting algorithm, the voting algorithm directly estimates the transformation parameters of
image instead of finding the one to one corresponding, making the image matching much more efficient and reliable.
Beside that, the method of handling the interior deformation problem caused by the incorrect splicing of three sub CCD
arrays is introduced. At last, a virtual combination of satellite image technique is introduced, the adjacent satellite images
in the same orbit are virtually combined to form a large image which is taken as the orientation unit, purposed on
accelerating the orientation process speed and decreasing the probability of orientation failure. With the techniques
mentioned above, the two main problems about CBERS-02B image: the inaccurate ephemeris parameters and the poor
internal accuracy caused by the incorrect splicing of three sub CCD arrays are solved successfully, the absolute
positioning accuracy reaches 1:10000 mapping accuracy and the internal accuracy reaches sub-pixel after the orientation
process. It indicates that extensive usage of Chinese high resolution satellite imagery may become possible and practical.

Registration of CBERS-02B satellite imagery in quick GIS updating

In this paper, the different methods of orientating different resolution satellite images with the existing vector maps are
introduced. To moderate high resolution satellite image, such as SPOT5 image, the vector road maps are often used for
the orientation, and the vector lines in the maps usually represent the road central lines. And to higher resolution satellite
image, such as QuickBird image, the vector lines in the maps usually represent the road edges, instead. Beside that, the
different extend of details of the images makes it necessary to handle them with different methods. Because in very high
resolution satellite images a lot of disturbing image features will be extracted along with the wanted one. A voting
algorithm is employed to solve the problem, the approach is based on the previous work where an edge-based voting
strategy was studied. The voting algorithm has the advantages of globally optimal and robust to noise. It can directly
estimate the transformation parameters, meanwhile providing the potential matches of edge points, these matches can
then be used in calculating the accurate orientation parameters, and providing the chance of change detection since the
unchanged objects can be marked out with this method.

Zuxun Zhang

Papers

Fully automatic generation of geoinformation products with chinese zy-3 satellite imagery

Estimation of Transformation Parameters Between Centre‐Line Vector Road Maps and High Resolution Satellite Images

Registration of CBERS-02B satellite imagery in quick GIS updating

Methods of orientating different resolution satellite images with the existing vector maps