Inverse proportional surface fitting-based image registration method for interferometric synthetic aperture sonar

Complex image registration is a crucial step in interferometric synthetic aperture sonar (InSAS) signal processing. The registration quality directly influences the quality of interferogram and subsequent reconstruction of digital elevation model (DEM). After the control points are determined, a geometric transformation procedure is needed in image registration. The traditional geometric transformation method is polynomial surface fitting. The polynomial surface fitting method is most suitable for far range, but it does not perform very well when the offset changes rapidly in near range distance. In this paper, a new InSAS complex image registration method based on inverse proportional surface fitting is presented to improve the accuracy and efficiency of InSAS complex image registration. Firstly, the relationship between offset and range is analyzed using the geometric model of imaging. The offset is an inverse proportional function of range, thus the inverse proportional surface fitting model is established. Then, the parameters of the inverse proportional surface fitting model are solved with control point pairs determined. Finally, the performance of the proposed model is analyzed by comparing it with the traditional second-order polynomial surface fitting model. The evaluation has been carried out using the root mean squared error (RMSE), calculation time and correlation coefficient as the criteria. A pair of images of the Qiandao lake, Zhejiang province in eastern China, are used in the experiments to validate the proposed method. The testing results indicate that the new method has the advantage of high accuracy and less calculation cost than traditional polynomial surface fitting method.