Comments: The most important reason for phase noise in repeat-pass interferometry is temporal decorrelation. It happens because the scatterer orientation and/or dielectric properties change between the two passes. Interferometry is extremely sensitive to this, as already changes on the scale of the wavelength are sufficient. Also very important is a precise coregistration of the two images. Already an offset of one resolution cell causes a complete loss of coherence. Other reasons for phase noise are low signal-to-noise ratio, SAR processing artifacts and finally spectral decorrelation due to the change of the look angle.