Nature of noise in 2D phase unwrapping

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Abstract
This paper reviews the concept of noise in 2D phase unwrapping of SAR interferograms. It is shown that phase gradient estimates derived as wrapped phase differences of adjacent samples are biased, leading to an underestimation of phase slopes. Hence, linear estimators like least squares methods operating on such gradient estimates tend to globally distort the reconstructed terrain. The slope bias is quantified as a function of coherence and number of looks both theoretically and via simulations. The particular type of noise under discussion also may lead to impulse-like errors in the phase unwrapped by a linear method. In order to avoid these errors the support of reconstruction must be restricted in the same way as with so-called branch-cut methods.

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