Ikonos Geometric Accuracy Validation

Since its launch in September of 1999, the IKONOS satellite has been consistently providing high quality 1-meter panchromatic and 4-meter multispectral images. Accurate interior and exterior orientation enable IKONOS to achieve high geometric accuracy with or without ground control. Exterior orientation is determined by on-board GPS receivers, star trackers, gyros, and interlock angles. Post-processing of GPS data with software incorporating sophisticated filtering and orbital modeling algorithms results in accurate ephemeris. Kalman filtering of gyro and star tracker data results in optimal combination of lower frequency star tracker attitude data exhibiting high absolute accuracy with high frequency gyro data being very accurate over short time intervals. Interlock angles relate the attitude and the camera coordinate systems and have been calibrated both pre-launch and in-flight. Initial interior orientation parameter values were determined by pre-launch measurements and later refined by in-flight calibration. In this paper, we shall first demonstrate the high accuracy of such calibrations based on test range data. Later, we shall quantify the geometric accuracy of the IKONOS camera using large IKONOS stereo image blocks with and without ground control, thus validating the exterior and the interior orientation calibrations.