Difference between vertical and LOS displacement


#105

It is very demanding processing, I would guess that it takes several months of solid work&studying to understand what is going on. You might be able to duplicate someone else’s processing but that is always risky as every case is different and without deeper understanding of InSAR and PSI troubleshooting will be hard. Whoever gave you this task should also understand this. I hope this helps!


Generate an interferogram with SNAP
About the STaMPS category
#106

Thanks for your support…


#107

Know someone who could make me a course or distance learning on this?
Please let me know.
Thank you.


#108

@ABraun alrady provided some useful links. You could also have a look at materials from the MOOC Echoes in Space - they have also some videos on youtube.
Otherwise you could apply to attend our Land Training Course 2018 http://eoscience.esa.int/landtraining2018/ :slight_smile:


#109

Ok thank you very much


#110

In the meantime, are there any online courses or old courses that can be downloaded?
I looked at the site you indicated to me but there is no material to download


#111

Good morning,
I have processed two images and I have obteined the displacement trought “Phase to displacement”.
Anyone knows how can I found the maximum and minimum displacement?
Thanks.


#112

Good morning,
I have followed the following steps in order to find displacement:

  • 2 SLC_IW images
  • Stack–> S1 Tops Coregistration
  • Interferogram Formation
  • Deburst
  • Topo Phase Removal
  • Goldstein Phase Filtering
  • Subset in my AOI
  • Export to Snaphu
  • Unwrapping in Snaphu
  • Import of “Subset” and “Unwrapped phase” in snap
  • Phase to displacement
  • Terrain Correction
  • Terrain correction - pixel value of a pixel with low displacement
  • Terrain correction of coherence taken from the import of snaphu
  • Band math–>if coh>0.6 then 1 else NaN, in order to have only pixels with high coherence
  • Stack between (high coherence) and (Terrain correction of displacement-pixel value)
  • High coherence * Terrain correction of displacement-pixel value

I think that my steps are correct considering what I have found in many user guide and in the suggests of this forum.
But I would like to know if the parameter setted and the conditions flagged or not for each steps are correct or not.
Following the screenshot for each steps:
I hope that someone can tell me if everything is correct or not.


Interferogram%20Formation
Deburst
Topo%20Phase%20removal
Goldstein%20Phase%20Filtering






Phase%20to%20displacement






#113

technically, your workflow seems right to me. It would be interesting however how the interferogram and coherence layer look.


#114

Thanks for your reply.
I have obtained the following values of displacement:

min: -0.096m
max: 0.053m

The strange thing is that I am sure that in some point of this area the displacement should be -10m.
Now I am tryng to do the same steps in an area where there was an heartquake in order to verify is my process is correct or not.
So, I have inserted and flagged the right data in all the steps that I have done?


#115

it is important to understand that DInSAR gives information about the spatial trends of a displacement. It is not a good idea to trust the values of single pixels as many factors are impacting the result.

Additionally, DInSAR measures the displacement along the line of sight, not the actual vertical displacement. Maybe this explains some of the discrepancies.

As suggested before, why don’t you assume the displacement of 10m at the area where you are sure and use it as the reference height for your displacement raster?


#116

I’m sorry but neither DInSAR not PSI can detect a large movement in a single pixel. Not even in the case where the scattterers were undisturbed, which is absolutely not the situation in your case. As I said earlier PSI might be able to detect a precursor subsidence at the site of the collapse, but since it is entirely possible that there was no precursor-movement, even that effort could well be futile.


#117

Because theoretically I have to found that value…


#118

Thank you.
At this point, however, I do not understand what this method is used for.
I have read many posts in this forum that explain how to get both LOS and vertical displacement by applying the following formula:
(Unwrapping phase * 0.055) / (- 4 * PI * cos (rad (incident_agle)).
I also found many ESA guides about the interferometry in order to obtain vertical displacement and the steps are the same of those I have applied.
Why I cannot obtain the desidered results?
Please explain it to me.


#119

Any movement in a single pixel (with stable scatterers) that is larger than 2PI in phase is ambiguous. It’s impossible to know whether that movement was Y or Y + N x 2PI where N is any integer. In other a words movement of Y, Y+2PI or Y + 76 x 2PI all produce the same observed phase. There’s no way around this limitation and there’s no way to unwrap the phase of such single pixel to retrieve the actual displacement.


#120

Good morning,
thanks for your reply.
I have applied into a single image (not into a stack of 2 images) the following steps:
-top split
-apply orbit file
-back geocoding

Now I want to obtain the phase information of this last product but I have only the intensity.
Do you know how can I obtain it?
I have tried with Interferogram Formation but it does not work considering that it works only with 2 images.
Thanks for your support.


#121

The phase information in a single SAR image is random and therefore useless.


#122

Ok.
I thought a thing, correct me if I’m wrong.
I could solve the problem you told me, proceeding in this way.
I could process the images individually, unwrapping the single image and only after doing the stack of two image so the interferogram formation.
In this way I would have the actual phase information for each image and not the difference.
I wanted to do this test but I got stuck at some point.
I have performed the following steps for the first image:
-topsar split

  • apply orbit file
    -back geocoding
    -deburst
  • goldestein phase filtering
    At this point I wanted to do the export on the snap to do the unwrapping but it is not possible because it wants the coherence.

Can you help meto find the coherence so I can proceed with this test and see if it works?
Thanks.


#123

Before debursting you shoud first create the interferogram, the coherence is produced here as well.
It seems like you follow a recipe without knowing about the meaning of the single steps.

ESA provides very good materials on this topic: http://www.esa.int/About_Us/ESA_Publications/InSAR_Principles_Guidelines_for_SAR_Interferometry_Processing_and_Interpretation_br_ESA_TM-19

Please also have a look at this tutorial: http://step.esa.int/docs/tutorials/S1TBX%20TOPSAR%20Interferometry%20with%20Sentinel-1%20Tutorial.pdf


#124

I know that I can obtain the coherence from interferogram formation but I cannot do the interferogram formation of a single image