SENSOR CALIBRATION OF THREE-LINE CCD SCANNERS ON ZY-3
ZY-3 is the first Chinese civilian high-resolution stereo mapping satellite. ZY-3 is equipped with three-line scanners (nadir, backward and forward views with 2.5 m and 4.0 m resolutions, respectively) and an additional multispectral scanner. In order to improve the mapping and positioning accuracy, sensor in-orbit calibration is a crucial procedure especially for high-resolution mapping-enabled satellites. The main focus of this paper is to describe the sensor calibration for ZY-3 sensors. Based on the experiences for other satellite sensor calibration, the following approach is proposed for ZY-3 sensor calibration in orbit: i) the initial internal geometric relationships of ZY-3 imaging sensors are established using the laboratory measurement and validation results; ii) assuming noise and errors are introduced once ZY-3 is launched, a further investigation is conducted to detect those changed geometric relationships and their associated parameters, and detect and reduce highly correlated parameters. A self-calibration method is applied to identify and correct those parameters. Geometric calibration field data is used together with simulated ZY-3 data to perform the self-calibration; iii) the newly obtained parameters are used to establish the final geometric relationships model of ZY-3 imaging sensors, and with the aid of ground control points and check points from the geometric calibration field, those parameters are to be validated, and the position accuracy is also assessed by applying ZY-3 image data. Although promising results were obtained using ZY-3 simulated data, the proposed approach for ZY-3 imaging sensor calibration is an ongoing research work and needs to be fine tuned in the coming months.