Calibration of Constant Angular Error for Cbers-2 Imagery with Few Ground Control Points

The rigorous geometric model which depends on physical properties of the image acquisition is the basic model for object positioning of high resolution satellite imagery (HRSI). Using the linear and angular elements provided by ephemeris and attitude measuring system carried on the satellite, the object coordinates can be determined by the rigorous geometric model when the image coordinates are given. Although attitude data measuring instruments have been improved in recent years, the precision of original attitude data acquired can hardly satisfy the requirement of direct georeferencing. For direct georeferencing application of CBERS-2 satellites developed independently in China, the ephemeris data are provided by MPSS (mission planning and supporting system) and GPS. The attitude data are provided by star sensor. After post-pass data processing, the error of ephemeris can be controlled within 20 meters, while the errors of attitude angles in all three axes (pitch, roll, and yaw) exceed 50 arc seconds.In this paper, the rigorous geometric model suited for CBERS-2 satellites containing a series of reference coordinate transformation is first introduced. The direct georeferencing results show that location root mean square error is more than 1000 meters for planimetry, the main part of which is systematic error caused by constant angular error (CAE). On the basis of the experiment analysis, a calibration model for eliminating constant angular error for CBERS-2 imagery is established. The calibration model can be easily realized and requires only few ground control points (GCPs).The calibration model has been tested on two scenes of CBERS-2 imagery. In each test, various numbers of GCPs have been used to calculate the CAE and the distinction of the results is subtle. Due to the sufficient SNR of CBERS-2 attitude data, the calibration model is able to reduce the location error to 50~65 meters for planimetry by single GCP, nearly 95 percent improvement to original result. It is significantly efficient especially under the situation of lack of GCPs. Further more, after calibrating the initial attitude, the model can provide refined initial angular elements for the following photogrammetry mission such as space resection and bundle adjustment of the imagery when enough GCPs are available. * Corresponding author.