Abstract: From the residue theory point of view, this paper gives a thorough study on the two kinds of mainly used phase unwrapping algorithms as well as a comparison. And then, the initial values and weights of weighted least squares algorithms are discussed and a synthetic weighted multigrid algorithm is given, which employs the fast and reliable output of Branch Cut method as the input of the multigrid algorithm to accelerate the convergence and uses a binary quality map derived from the phase derivative variance as the weights to make the algorithm more robust and reliable. Phase unwrapping results of X SAR  data have shown the validation of the analysis.

Key words: inter ferometr ic SAR, phase unwr apping, phase der ivative, va ria nce, synthetic multigrid algorithm