What if displacements are greater than half wavelenght?

Microwave Toolbox Interferometry
#1

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?

#2

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
#3

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.

#4

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

#5

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