nice! Please do so 
I am using the following steps:
- Coregistration (in the warp tab, I use the bicubic interpolation method)
- Interferogram Creation (I also check the box for removing the topographic phase and include coherence estimation in this step, I see some people advise this as a separate step)
- Goldstein Phase filtering
- SNAPHU export
- SNAPHU Phase unwrapping (so far I have had success using only the DEFO method)
- SNAPHU import.
- Phase to displacement
- Range Doppler Terrain Correction
Hey i have been following these above mentioned steps for interferometry but I m getting error at snaphu export.I’m using ALOS 2 PALSAR2 data in snap 7.0.
Thank you
Please describe your error.
Hello sir, I have been trying for interferometry in snap software. As the steps mentioned above by the ballistic I have followed them. but I am getting an error when I perform phase unwrapping. The steps were coregistration, interferogram creation, phase filtering, and SNAPHU export. After this export, there were coherence and phase images, which were not opening in snap software. I am not sure where I have done the mistake. and the screenshots of the results ha been attached.
Thank youphtos.docx (3.9 MB)
as you are using a quad-pol product, i recommend to use the “select band” operator at the beginning and perform the workflow on HH first to test if everything works alright. The images you currently show include all polarizations, which does not make much sense at the beginning. Please check how phase quality can differ for the polarimetric bands: Effect of polarization on interferometric products
The SNAP workflow for polarimetry you described is working with single polarization images, so I recommend to repeat it with only one polarization at a time. Then your interferograms should look more typical (currently, you are displaying an RGB image of several bands).
Maybe also this tutorial helps you: Interferometry Tutorial with Radarsat-2 It was based on Radarsat-2 images, but the steps are the same for ALOS-2.
Thank you so much sir, I will surely try and attach the results as soon as I complete.
That is my mistake. I was working only with the HH band in my workflow. I will update my post.
I should be clear, I am working with only the HH band, the images I used were quad pol. I used the band subset to choose just the HH information
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Hello Sir, I have been trying interferometry by using only one polarisation. I got stuck at the SNAPHU export step. When I export the image file of the unwrapped phase is missing. I am not getting what will be the reason for this. I have attached the screenshots of the processing steps. please provide me the solution for this error. Thank you.images interferometry.pdf (518.7 KB)
before you can import the unwrapped phase, you have to create it by executing snaphu.
Please check the instructions regarding snaphu in this tutorial: Sentinel-1 TOPS interferometry
Hello,
I have been trying for snaphu unwrapping. Even after following the steps from the above pdf still it showing the error and phase unwrappin is a problem. I am not getting whther there is problem with the system im using or software. please suggest something so that i can try.
please help us understand your case:
- were you able to execute snaphu correctly?
- has the unw_phase…img file been created sucessfully?
- please specify “still it is showing the error”
SNAPHU is very particular in that you HAVE to set up the inputs correctly. This can be a bit hard to follow at times if you have not been diligent in setting up how you write your new data.
This is not perfect, but it is a more detailed workflow of the steps I took.
PALSAR 2 InSAR Workflow in SNAP.docx (855.7 KB)
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Dear all,
I have tried to process the ALOS-2 data to generate an interferogram for co-seismic surface deformation in Japan.
I can obtain a clear interferogram after the “Goldstein Phase filtering” step. However, I’m puzzled by the presence of noisy signals in the sea area. I assumed that the sea should be an area with no signal. The result is shown below. Is this outcome reasonable? Thank you for your kind assistance.
If your coherence-window is very small spurious coherence will appear also over the sea. Try a larger coherence-window like 9x something or even larger.
Hi @mengdahl
Sorry for the delay in responding after such a long time. Thank you for your suggestion.
I have tried to add the coherence range window size to 100 in the “Interferogram Formation” step. And use coherence mask in the Goldstein Phase Filtering. The parameters I set as follow
The presence of noisy signals in the sea area still exist. The interference ring is even gone.
Also, I feel that the interference ring I initially obtained is quite peculiar. It seems more like orbit errors rather than coseismic deformation caused by an earthquake?
I’m not quite sure where I went wrong. The steps I used were Coregistration, Interferogram Formation, and Phase Filtering.
Could you provide me with some advice? I hope to use SNAP to process ALOS-2 images and obtain coseismic deformation from the Japan earthquake in January of this year.
Thank you very much!
Hi @mengdahl,
I apologize for bothering you again, but I really need some assistance. Could you please provide me with hints or suggestions to address my issues? Thank you very much!
Your temporal baseline of 1.5 years is long. Try starting with a shorter baseline as then you are likelier to have better coherence overall.
ps. I find it odd that in your example above the interferogram appears to be pure noise (coherence 0) but your coherence image disagrees.
Thank you for your suggestion.
I have tried using an image pair with a shorter temporal baseline (2023/6/6 & 2024/1/2) to generate an interferogram. The steps I followed are:
- Coregistration
- Interferogram formation (I have checked the topographic phase removal option for deformation)
- Phase filtering (changed the FFT size to 256)
The following is the result. The interferogram still looks very strange. It also shows lines in the horizontal direction.
I found the interferogram generated by others as below.
(TRE ALTAMIRA on LinkedIn: #earthquake #noto #japan #fault #grounddisplacement #alos2…)
The interferogram differs from my result, despite using the same images. I would appreciate your assistance in addressing this issue. Thank you very much.