Topography Reconstruction by Interferometric SAR Look Vector's Orthogonal Decomposition

Topography reconstruction by interferometric synthetic aperture radar (InSAR) refers to a method used to determine target's three- dimensional (3D) position. This position is obtained by principal measurements and the imaging geometry of system. By coherently combining signals from the conventional and additional SAR antennas, the interferometric phase difference between the received signals can be formed for each imaged point. In this scenario, the phase difference is essentially related to the geometric path length difference to the image point, which depends on the topography. The range equation, the Doppler equation and the interferometric phase equation of InSAR provide the relation between the fundamental measurements and the point's position on topography. So the point's position may be obtained by solving three interferometric equations. The InSAR equations contain the unknown point's position in a highly nonlinear manner and are difficult to be solved directly. For this problem, researchers have resorted to the orthogonal decomposition of the look vector of radar and have derived several reconstruction algorithms. In this paper, we analyze the topography reconstruction algorithm based on Madsen's orthogonal decomposition (MOD). We show that the plane wave model has been introduced in the derivation of this algorithm which causes a significant reconstruction error especially for airborne case.