A differential interferogram (DInSAR) can be composed if the phase of one interferogram is subtracted from the phase of another interferogram "DEM" so that the remaining contributions in the phase are those related only to surface displacement.
but how it can be extracted or converted from phase units to metric units displacements per unit time (e.g. cm / year) ?
Down load the „InSAR Principles: Guidelines for SAR Interferometry Processing and Interpretation” from the ESA homepage and you will find the answer.
Dear Laszlo,
Thanks for your answer
But in practical approach What is the final form of the displacement map generated from ERS interferometric data?
Cheers
The radar is sensitive to surface displacements in the radar line-of-sight. Conversion of phase to cm is based on the wavelength. One fringe corresponds to half the wavelength, i.e. 2*pi radians = - lambda/2. For ERS lambda is about 5.6 cm. In terms of the sign convention a range increase (read positive phase values), mean the radar signal has travelled longer. In other words if reflects a subsidence motion. Therefore a minus sign is often included when converting the phase to a displacement.
If you are looking to an interferogram then the units are in rad. You can convert that to a velocity by dividing by the temporal baseline of the interferogram.
Conversion to a North, East and Up component is not trivial. To decompose the LOS for NEU components you will need to make some assumptions. For that I refer you to the literature as suggested by Laszlo.
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