Phase unwrapping method based on multi-frequency InSAR in highly sloped terrain

In highly sloped terrain, the interferometric phase gradients of the adjacent pixels are more than π. Therefore, the conventional phase unwrapping methods cannot correctly obtain the absolute phase. To solve this problem, a phase unwrapping method based on multi-frequency interferometric synthetic aperture radar (MF-InSAR) is proposed. In this method, a joint probability density function based on MF-InSAR is established to estimate the phase gradient in highly sloped terrain, and thanks to the small changes of the phase gradient differences between adjacent pixels, an adjacent set of the phase gradient is further proposed to improve the robust of this algorithm. After the reconstruction of phase gradients, the branch-cut phase unwrapping method is used to obtain the ultimate absolute interferometric phase. Computer simulation proves the proposed method can correctly obtain the absolute interferometric phase in highly sloped terrain, which makes further efforts to acquire a better reconstruction accuracy of DEM.