What if displacements are greater than half wavelenght?

Hello Everyone,

After using SNAPHU and generate displacements, I obtain some values greater than the sensibility of the Sentinel 1 IW sensor. That is if theoretically, the maximum displacements that can be obtained are half wavelenght: 0.5 * 5.4 cm = 2.7 cm, I got even 0.031 m. How should I interpret these results?
Is there any method to filter or correct these results or it is possible to reach these magnitudes?

unwrapping is prone to errors, especially in noisy areas. There is little reason to trust the maximum displacement values, because they are very likely not feasible. What matters is

  • the quality of the interferogram before unwrapping
  • the amount of low coherence areas
  • the spatial distribution of displacement
  • the histogram of displacement values (e.g. is the mean feasible?)

Even if all preconditions are perfect (which is rarely the case for repeat-pass DInSAR) you should not give too much on the extreme values.

Please also have a look at these materials: Echoes in Space - InSAR error sources

1 Like

Thank you very much Abraun.
So, to consider a more reliable range of displacements would be a good practice if I mask values (absolute value) over half wavelength. And, in addition, if I mask the values within the standard deviation, considering that these values belong to the residual phase (topographic, atmospheric, and other effects) and noise. Or should I consider also a range close to 0 m, enclosed in the residual range, as representative of the stable areas?
Please, I thank every response, example, article, or guide on best practices to classify and interpret InSAR results.

I would rather mask out low coherence areas and then see what is left

Thank you for your advices ABraun. At the end is good idea using coherence as the quality constraint for results.