Determination of Optimum Tie Point Interval for SAR Image Coregistration by Decomposing Autocorrelation Coefficient

Abstract

Interferometric synthetic aperture radar (InSAR) is a well-established technique for the generation of digital elevation models and/or the measurement of ground surface deformations. In InSAR data processing, the first step is the image coregistration achieved by using a set of tie points which are the conjugate image points on both master and slave images. To achieve reliable coregistration, a set of points is used instead of a single point. The interval of tie points, i.e., tie point density, will greatly affect the reliability of the coregistration. Hitherto, there have been no effective methods for the determination of optimum tie point interval for the purpose. In practice, this parameter is determined by experience. In this paper, a method for determination of optimum tie point interval is presented based on theoretical analysis of autocorrelation coefficient of SAR image, which reflects the similarity between image pixels. After computation of autocorrelation coefficient in range and azimuth, it is decomposed into low and high frequencies by a wavelet transform. Then, by a combined analysis of the variations of wave amplitudes with distance, the optimum interval for tie point matching can be determined. It is found that the optimum tie point interval in azimuth and range can be different. Two pairs of SAR images acquired by different platforms are used to validate the proposed method. An optimum tie point interval can be determined in this way for any pair of SAR images.