A Simplified Ortho-rectification Approach for Satellite Imagery

A novel ortho-rectification approach for satellite imagery, which we name the ‘three-model approach’, is proposed. Rather than fitting a single model, as is typically done, this approach fits a sequence of three models. The first model estimates the azimuth of the image, the image scaling factor and image shifting; the second model estimates the overall image pitch/shearing angle; and the third model estimates the image roll and swing angles and the affine transformation coefficients. The first and second models are linear while the third model is non-linear. Unlike other ortho-rectification approaches which require sensor and orbital ephemeris information and large numbers of control points, the three-model approach requires only the rough satellite orbit height above the earth’s surface and a minimum of only four control points for the whole process. In experimental trials, this new approach has been tested and compared with established implementations of rigorous satellite orbital modelling. Overall, the results from the three-model approach for satellite image ortho-rectification are promising in comparison to the rigorous satellite orbital modelling. The three-model approach is easy to understand (it has a clear physical meaning for each model) and the implementation is very simple. The biggest advantage of the three-model approach over other approaches is that it does not require good approximations for parameters and other associated information (such as ephemeris data). In addition, to ensure minimal residuals within a production environment, the proposed three-model approach employs a robust estimation technique. Results from several trials demonstrated that the proposed approach is a good alternative for real production work.