A generalized search scheme for automatic registration of remote-sensing data

A generalized search scheme for automatic registration of level-1 data of multiresolution and multi-sensor remote-sensing data was proposed. The robustness and time efficiency of the automatic registration process is critically dependant on the search scheme for identification of control points. The proposed method consists of three levels of search ranging from coarser to finer. This process was found to be capable of registering images to sub-pixel level which are independent of rotation and scale variations, and also translation that vary by few metres to kilometres. In order to reduce the low pass effect due to multiple transformations involved in the multi-level registration process, a direct correspondence between the reference image and target image was established so that a single resampling needs to be applied. This correspondence also helps to generate products at any desired pixel size and to keep the original resolution intact. In this scheme mutual information (MI) is used as a similarity measure and a non-rigid transformation, thin plate spline (TPS), is used for achieving sub-pixel registration accuracies. MI is found to be better for identification of match points even for images that are radiometrically nonlinear. Unlike global transformation methods, use of non-rigid transformations such as TPS achieves sub-pixel accuracy in the moderate hilly regions as well as high hilly regions where relief displacements are high, provided sufficient number of control points are generated. However TPS transformation demands accurate control points. A robust method for detection of inaccurate control points was adopted and explained in the paper. The scheme was tested on a number of combinations of remote sensing data of the same resolution and different resolution datasets, namely Cartosat-1 with Liss-4 of Resourcesat-1, Landsat Thematic Mapper (TM) with IRS-1C/1D and Cartosat-1 with Enhanced Thematic Mapper (ETM). The results are presented along with accuracies achieved.