The geometric correction of SPOT 5 HRG images using an orbit attitude and minimum control points

Using supermode processing, SPOT 5 images have significantly improved ground resolution of 2.5m by two arrays of CCD detectors vertically and horizontally offset by one half-pixel (2.5 m) in the focal plane. SPOT 5 also provides the corrected attitude angles of satellite's orbit with a geometrically optimized system. Consequently, SPOTS has more precise geometry than other SPOT system. Although various mathematical model for SPOT 1-4 image to correct the geometric distortion have been proposed by many researchers, the model for SPOT 5 images need to be further improved using a geometrically optimized system. In this paper, the method to correct the geometric distortion for SPOT 5 HRG images using orbit attitude information and minimum control points was studied. This method was based on the assumptions that the satellite is moving along a well-defined close-to-circle elliptical orbit, and the orbit taken by auxiliary data is similar to the original satellite's orbit. Using these assumptions, two new equations were formulated from the geometry of the satellite. If the orbit of SPOT 5 is very precise, these equations can be directly applied using the initial parameters. But, these parameters must be updated because the initial information has the errors. LOS (Line Of Sight) vector, which is expressed by the look angles, is used for the updating parameters, because two equations are expressed by look angles of the satellite in the space, and then are dependent on the pixel direction. In order to confirm the applicability of this method, 30 check points acquired by GPS survey were used. After the residual of two equations were corrected by the updated parameters, the RMSE of check points in two equations were about 1.37e-6 and 1.70e-6, respectively, and the coefficient of determination (R²) of them were about 0.999 and 1.0, respectively. These results imply that LOS vector can be used for the updating parameters, and mean that our method is very available. Finally, another two GCPs(Ground Control Points) acquired by GPS survey were used to correct the distortion of geometry. The result of correction was that the RMSE for 30 checking points was 0.61 pixel in pixel direction and 0.47 pixel in line direction.