DSM Generation and Interior Orientation Determination of IKONOS Images Using a Testfield in Switzerland

We present processing of Ikonos triplet images over a testfield in Thun, Switzerland with accurate ground control points, 1600 m height range, variable land cover and suboptimal imaging conditions (snow, long shadows). A sophisticated matching algorithm for DSM generation is presented and the results are compared to reference data from airborne laser scanning. The RMS errors for the whole area, excluding vegetation, were 2-3 m, while for bare ground the accuracy is about 1 m or less. The accurate matching allowed the detection and quantification of errors in the interior orientation of the sensor, caused by changes in the relative position of the 3 CCDs forming the virtual CCD line. These errors were verified through a cooperation with Space Imaging and recomputation of the sensor interior orientation. The interior orientation errors caused height jumps of 1.3 to 1.5 m along two stripes at the overlap regions of the 3 CCDs. The method used for the detection and quantification of these errors is applicable for in-flight calibration of sensors forming a virtual image through butting of multiple CCD arrays, without the need of testfields with signalised points, which are difficult to establish and maintain. Depending on the accuracy of the matching method and of the reference DSM, we estimate that this in-flight calibration method can detect interior orientation errors causing parallax errors of 0.5 pixels or more.