There are two ways for interferometry
a. apply an external DEM like SRTM
b. Apply a third SAR image to an interferometric pair
if an External DEM is applied with low accuracy about ten meters or more how is sub-centimeter accuracy achieved ???
Hi Reda,
it achieves it in a relative manner. DInSAR is not an absolute measurement principle. So what you actually measure is the relative change in distance from time 1 to time 2. You assuming your DEM therefore as "correct", or in a more technical way, you use it to substract the topographical component of your interferometric phase. In addition, 2-pass DInSAR does not achieve necessarily sub-centimeter accuracy. Atmospheric conditions might have strong effects (e.g. 14cm for 20% change in relative humidity). If you want to achieve sub-centimetres accuracy, go for multi-temporal approaches like SBAS and/or PS. Those techniques provide you also an DEM error estimation as an additional output. There are some freely available open-source software packages out for research purposes. StaMPS or GiANT for example.
Good luck,
Andreas
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