# Difference between vertical and LOS displacement

Thanks.
I will try and I will let you know if I have some problems

So,
I’m going to proceede in this way:
I will download 2 IW_SLC_descending images of an area and 2 IW_SLC_ascending images of the same area.
In order to obtain the vertical and horizontal displacement I have to follow the following steps:

• S1 TOPS coregistration of the 4 images
• Interferogram formation
• Deburst
• Topo phase removal
• Golden phase filtering
• Subset
• export to snaphu
• unwrapping on SNAPHU
• import the result on SNAP

Vertical displacement:
(unwrapped phase * wavelength) / (-4 * PI * rad (cos (incidence angle))) with wavelenght= 0.055m

Horizontal displacement:
(unwrapped phase * wavelength) / (-4 * PI * rad (sin (incidence angle))) with wavelenght= 0.055m

• Terrain correction of vertical and horizontal products

• I will mark the value of displacement_Terrain Correction in a high coherence point (taken from the coherence band obtained by unwrapping)

• Terrain correction_Vertical displament - pixel value with high coherence

• Terrain correction_horizontal displament - pixel value with high coherence

• Terrain correction of the product obtained from the subset

• Math band with the following formula:

If coherence band> 0.6 then 1 else NaN

• Stack respectively between:

Terrain correction_Vertical displament - pixel value with high coherence and high coherence
Terrain correction_horizontal displament - pixel value with high coherence and high coherence

• maths bands:

Terrain correction_Vertical displament - pixel value with high coherence * high coherence
Terrain correction_horizontal displament - pixel value with high coherence * high coherence

Is it right?
Can I proceede in this way?
best regards

Good morning,
can I have a feedback please?
Thanks

Good morning,
please, could you explain better this sentence:
In order to verify your results, you need GPS measurements for your AOI
Thanks.
Have a nice day.

Please be aware that unless the deformation signal is very large, it will be masked by atmospheric artifacts. If your signal of interest is small you will need to do PSI-processing with a long stack of images.

2 Likes

can you help me about my last questions?

When we derive the ground subsidence results using interferometry, we need to validate them and see whether we are close to the ‘true’ subsidence values or not. IN order to do that, we need to validate the results against an equally accurate technique with is the GNSS.

GNSS provides very accurate measurements and it is usually used against InSAR results. The problem is that, it is hard to find GNSS measurements for your area of interest. Finding validation data is always very challenging.
Also, you might find other studies conducted on the same area you are working on and be able to validate your data.

By the way, mengdahi is right on his commend.

Thanks.
I know that the PS method is better for this study but I have found a lot of difficulties instead I have found a lot of manual and user guide about the study of interferometry with snap and snaphu…so in this moment I prefer to use snap and snaphu.
In future I would like to use stamps hoping to find support.

do you think that the steps that I have followed with snap and snaphu are correct?

Good morning,
I have a problem with the Stack of the images.
When I try to do the stack, snap says that I have to do the TOPS coregistration with the kind of images that I’m using.
But when I do the TOPS coregistration I have the chance to use only 2 images.
How can I solve this problem considering that I’m using 2 ascendent images and 2 discendent images?
I have thought to do first the stack between the two ascendent images, after between the two discendent images and at the end the stack between the 2 results.
Is it correct or there is another way?
Thanks.

My solution does not works because I cannot stack two stacks.
Somebody has a solution for me?

I have tried with the graph inserting 4 read and in this way it should works but I have the problem that the subswath of ascending and descending images are different so I cannot select the same subswath and the process does not run

The image stack is executed at the very end.

1. you need to perform TOPS co-registration using the two SAR images (one ascending and one descending). Make sure that the sub- swath of the ascending image is the same with the sub-swath of the second image.

2. Repeat the fist step for the rest of your dataset

3. Perform the stack

This will not work. InSAR is only possible with images from the same orbit track.

3 Likes

Ok thank you very much.
I have understood throught this forum and other document that in order to have a sure vertical displacement, I should process images with ascendent and descendent orbit.
Is it true?
If yes, how can I do it if is impossible stack them?

You need an ascending stack and a descending stack.

And then?
How can process them together?

If you want to have a "sure" vertical displacement you would need to do PSI-processing on sufficiently large ascending and descending image stacks. This is not an easy thing to do. Processing a pair of images will not work since atmospheric disturbances usually completely mask the deformation signal.

thank you so much.
I was hoping it worked out considering that I found many user guides, manuals and discussions on this forum explaining how to find vertical displacement with snap and snaphu.
In any case, I do not know how to do the PS method and it is very important that I deliver this work.
Is there anyone who has already done it and can explain to me step by step what to do, what other software do I need and how to install them?
I looked for on the web and I have found a few infirmations and the little information found only confused me.