Improving Phase Unwrapping Techniques by the Use of Local Frequency Estimates

In multi-pass space-borne SAR interferometry, the two acquisitions often present low correlation levels and very noisy phase measurements which are incompatible with automatic phase unwrapping. Instead of dealing with many residues due to erroneous wrapped phase differences, we propose to use the local frequency as measured by a spectral analysis algorithm presented in a previous paper [1]. For this purpose we present two conventional unwrapping algorithms, one local, the other global, that we revisit to benefit from the robust local frequency estimates. For a local approach based on path following techniques, we use the frequency estimates in a slope compensated filter which extend the complex averaging up to a sufficient number of look to eliminate residues due to the noise. Then we connect residues due to non-interferometric features along mask components resulting from the detection of lay-overs and uncorrelated areas. For a global approach such as weighted least squares methods, w..