Fringe Estimation in Distributed Scatterer Interferometry

In distributed scatterer (DS) interferometry, fringes within a multilooking window can cause bias on coherence estimation and degrade phase-linking precision. Furthermore, fringes might also bias the estimated consistent phases. The problem can be solved by estimating and removing these fringes, i.e., defringing; however, imprecise estimation can significantly affect the results. Thus, a new defringing method for DS time series analysis is proposed. Different from the previous defringing methods, the new method makes use of the information from redundant interferometric combinations under the assumption of Gaussian speckle, and a series of consistent fringes with a single reference can be obtained. The basic idea is to establish a framework of weighted least square adjustments with gross error elimination, exploiting the triangular consistency of fringe frequencies as a constraint to estimate fringes. The statistical properties of fringe frequency estimation were exploited to determine the optimum choice for the weight matrix. The quality of the estimated fringes can be improved significantly using the proposed method and therefore the quality of consistent phases in nonstationary areas can be increased. Simulated and real data experiments demonstrate the effectiveness of this new defringing method.