Analysis of Terrain Elevation Effects on Ikonos Imagery Rectification Accuracy by Using Non-Rigorous Models

In the absence of sensor calibration and satellite orbit information for Ikonos satellite imagery, empirical methods have to be adopted for the geometric correction of the images. This paper addresses two major terrain related issues. First, the paper focuses on the effects of terrain variation on the rectification accuracy of Ikonos images using various two-dimensional (2D) transformation models. It was found that (1) the accuracy of rectified coordinates is significantly affected by elevation differences - the greater the differences, the lower the rectified accuracy; (2) for higher accuracy results, ground control points (GCPS) should be projected to a compensation plane before 2D transformation models are applied; and (3) an accuracy of about 0.5 m RMS error can be gained from rectified Ikonos images by utilizing most 2D transformation models when accurate ground control points are available. Second, the paper addresses the effects of terrain variation and the number of GCPs on the obtained ground points accuracy when an eight-parameter affine model is used for 3D ground points determination for stereoscopic Ikonos imagery. It was found that (1) non-collinearity-based 3D orientation and triangulation model can be used successfully in most cases for 3D ground point determination without the need for a camera model or satellite ephemeris data; (2) accuracy up to the sub-pixel level in the X-Y directions and about one pixel in the Z direction can be achieved; (3) the model works significantly better for hilly and mountainous areas than very flat areas; and (4) the accuracy of the results can be improved significantly either by increasing the number of GCPs or by adding topographic constraints.