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In-orbit geometric calibration is a key technology for improving the geometric positioning accuracy of satellites. Conventional geometric calibration, which uses high-accuracy ground control data to accurately calibrate the orientation parameters of a satellite, heavily relies on the control data of the calibration fields and may not be applicable in emergencies where urgent and accurate positioning is needed. The constant calibration of satellites is also difficult owing to the lack of permanent calibration fields. This paper presents a geometric cross-calibration method for the rapid and accurate calibration of satellites. The conjugate points from the multitemporal images of one satellite or multi-satellite images are first automatically extracted; then, the interior orientation parameters of the satellite requiring calibration can be precisely recovered according to the positioning consistency constraint of the conjugate points. In contrast to the conventional method, the proposed method can accurately calibrate the orientation parameters without using high-accuracy control data of the calibration fields. Therefore, the proposed method aids in the constant calibration of satellites to ensure the positioning accuracy, even without sufficient permanent calibration fields. The multitemporal images of the Yaogan-4 satellite and the images of the ZY3-01 and ZY02C satellites were considered for verifying this method. Finally, accuracies of approximately 0.7 and 0.6 pixels were achieved by the proposed and conventional methods, respectively. The difference between the two methods was only approximately 0.1 pixels, demonstrating that the proposed method can achieve a calibration accuracy as high as that achieved by the conventional method, even without the use of high-accuracy control data. [ABSTRACT FROM AUTHOR]

Design deficiencies and hardware limitations cause a number of issues with the images acquired by Chinese satellites launched before 2012, such as YG-12. The geometric quality of the images recorded by YG-12 cannot match its high resolution because of serious time-synchronization errors and interior distortions. To improve the geometric quality of YG-12 images, this paper proposes a method of interior calibration for the YG-12 panchromatic sensor. In addition, an innovative method is proposed to eliminate time-synchronization errors using parallel observations of the panchromatic sensor onboard YG-12. The experimental results indicate the interior parameters of the panchromatic sensor are determined with an accuracy of better than 0.32 pixels, and seamless mosaic images can be obtained after the elimination of distortions. Furthermore, the positioning accuracy with relatively few ground control points is shown to be better than 1.5 pixels. [ABSTRACT FROM AUTHOR]

For the problem of block adjustment for satellite images, which cannot be solved under conditions of weak geometric convergence, this paper proposes a strategy that uses a planar block adjustment method to solve the orientation parameters of all satellite images, and then each satellite image is orthorectified. This strategy can ensure both the uniformity of the positioning accuracy and the strictness of the relative positions of the adjacent orthoimages. Tests of 139 panchromatic nadir images from the ZY-3 satellite show that by using only a small number of ground control points (GCPs), whose plane accuracy is 5 m, the plane accuracy of independent check points (ICPs) is better than 7 m after planar block adjustment. This accuracy meets the requirements for Chinese 1:50 000 topographic maps. Moreover, the preciseness of tie points (TPS) in adjacent images is better than 0.5 pixels, so a seamless level in mosaic geometry is attained. [ABSTRACT FROM AUTHOR]

The ZiYuan-3 satellite allows users to obtain triplet along-track stereo and four-band multispectral images within a single pass. Its basic sensor-corrected products are generated by reimaging with a virtual CCD array in which inner and exterior distortions are resolved and the introduced errors are negligible. In this study, three zY-3 datasets (Dengfeng, Anping, and Taihang) were used to evaluate the accuracy of bundle adjustment using triplet stereo images. For both standard and long-strip scenes, the RMS errors of plane and elevation were 2.6 m and 1.6 m, respectively, when ground control points (GCPs) were deployed around the corners. The digital surface model (DSM) of the Dengfeng dataset was compared with a reference DEM (1:2000); the RMS errors produced varied with topography, with values of 3.9 m, 6.4 m, and 6.8 m for plain, hilly, and steep mountainous areas, respectively. [ABSTRACT FROM AUTHOR]

The internal geometric distortion of charge-coupled-device (CCD) chips degrades the internal geometric accuracy of satellite images. Even if a large number of ground control points (GCPs) are used for geometric correction, the satellite images cannot always be used for direct mapping. Because of the current lack of core parameters for building a rigorous geometric model, this paper proposes a combined interior-orientation calibration method based on the rational function model (RFM) for multiple GF-1 wide-field-of-view (WFV) images of the same general scene. A polynomial model of look angles in the image space is chosen to compensate for the systemic error of CCD chips. After calibration for sensors 1 to 4, the orientation accuracy is improved to 0.4 pixels. Moreover, the residual error figures show no obvious trend. Other GF-1 WFV images are calibrated using the obtained interior-orientation parameters, and the improvement in their orientation accuracy is demonstrated to validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]