| ZY-3is the first Chinese civilian high-resolution stereo mapping satellite, equipped with three-line scanners (nadir, backward and forward) and an additional multispectral scanner.Due to the successful launch of ZY-3, it is possible to quickly create a nationwide scale1:50,000topopraphic maps and long-term continuous revise and update the1:25,000or larger scale maps. Before the launch of ZY-3, the equipped scannes were calibrated through a series of the high-accuracy works in the laboratory. The calibration’s results provide the geometrical parameter information for the image processing on the ground. Satellite is impacted by the various momentum and disturbing force during the satellite’s launch and by microgravity and ambient temperature changing during running in its orbit. All these factors casue the parameters calibrated in the laboratory no longer apply to the processing of satellite’s data subsequently. For the reason, the sensor’s paramteres must be carried out the in-orbit calibration and build the corrected relationship between the image and ground points, in order to ensure the high-precision mapping and geometric positioning for satellite ZY-3.In order to ensure and improve the geometric positioning and measurement accuracy of ZY-3satellite, this paper studies deeply the theory and algorithms of three-line array calibration in orbit basing on the structure and imaging’s characteristics of cameras on the ZY-3. The main contents of research are introduced as follows:1) Analyzing of imaging and structural characteristics of the three-line sensorsStudying the relative positional relationship between the study three line sensors, Splicing structural characteristics of CCD-lines equipped in the bforward, nadir and backward sensors and the relative spatial structure of each CCD chip provides the theoretical basis and references for the algorithms of self-calibration and the research of error model base on the data about the sensor’s forcus, principle point and initial distoration of CCD-Line, and provides the initial value for the block adjustment of additional parameters’self-calibration in order to ensure the accuracy and stability of computation.2) Establishing the rigorous imaging model of the three-line array sensors on the ZY-3Based on the coordinate system of ZY-3satellite, the geometric relationships model of the various components’ ZY-3are builded up. According to the strcture data of satellite, scanncers’date and laboratory calibration’s data, the relationships between the star sensor and the coordinate of satellite’body, betwwen the dual-frequency GPS and the coordinate of satellite’body and between the nadir, backward and forward sensors and the coordinate of satellite’body. Using these relationships establishs respectively the rigorous imaging models for the nadir, backward and forward sensors. 3) Proposing and researching the polynomial model of point-by-point with weight for interpolating the satellite’s attitude and orbitThe polynomial model of point-by-point with weight is proposed according to the researching and analyzing the data of ZY-3’s orbit and attitude in the long and shot period. Using the polynomial model of point-by-point with weight, the general polynomial model, piecewise polynomial model and orientation image method interpolated the the data of ZY-3’s orbit and attitude. The result and accuracy are analized and compared. The two forms of interpolation of the polynomial model of point-by-point with weight are established and the differential forms are derivated out. The new model for interpolating orbit and attitude can get a higher accuracy, have a better flexibility and can reduce the correlation amony the exterior orientation elememnts.4) Establishing and analysing the internal systematic error model of sensors on ZY-3Two kinds of internal the orientation system error model, the error model with physical parameters and the piecewise polynomial error model, are proposed during analyzing the factors that may cause systematic errors. Each parameter in the physical parameters error model has the obvious Physical meaning, but the parameters in the model based on piecewise polynomial error model have not the Physical meanings. The physical quantities of the satellite’s sensors are included implicitly in these parameters. According to the experiments of the self-calibration in-orbit, it is obvious that the piecewise polynomial error model can reduce the correlation amony the various parameters of the system error and ensure the accuracy and reliability of parameters’result. Comparing the accuracys of two models, the piecewise polynomial error model can attain a higher accaurcy for compensating the system errors.5) The partition of GCP method for calibration in-orbit basin on the GCP’s distributionBasing on the structure of sensors on ZY-3and the data of attitude and orbit, the method of calibration based on the partition of GCP is proposed according to studying the different accuracy of in-orbit calibration using the different distribution of GCP. The kind of method of calibration is that the image covered the GCP is parted into several narrow strip areas in the direction of push of CCD line array. The wide size of partition is determined by the distribution and the number of GCP. The number of GCPs covered by the image’s partition needed to be sure about the accuracy of parameters. The results of parameter solved by the GCP in the different image partition are averaged to improve the accuracy and reliability of the parameters’result according to reducing the random error arising out of some factors... |
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