S1 TOPSAR Interferometry on S1TBX - Further improving interferogram coherence

HI,

As ABraun said mentioned, if your coherence is low, no fringes are formed, hence, you have just random phase. By looking at your SAR image, it looks like the coherence is low apart from a few areas in your image. The quality of the interferogram is heavily depends on the coherence.

I guess that what you are trying to do is to estimate movement/subsidence on the ground ? if yes, then areas with random phase (low coherence areas) cannot be used for estimating movement or subsidence. You may need to look at your coherence map.

In terms of the second image, it looks like the coherence is high, hence, the nice fringes.

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I think coregistration also plays a major role in the resulting quality of the interferogram. Besides that, Multi-looking, filtering or the quality of the DEM could have differed in the cited study which all increase or decrease quality of your fringes.

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@mauleon.fb I can’t imagine the coherence being that bad with just 6 days between passes. Did you use the same subswaths in each scene? Do they sit on top of each other well, or is one subswath different from the other? Did you use S1 TOPS Coregistration? Did you check the modeled coherence after coregistration? (Radar > Interferometric > InSAR Stack Ov erview) Add your files and run the overview. The modeled coherence should be as close to 1 (or 100%) as possible.

Are you sure that the interferogram you are trying to replicate was processed using the same exact datasets? Was ESA SNAP used for this?

@ABraun I performed the topographic phase removal yes because i needed to create a subsidence map after an earthequake which is on July 6.

As for the coherence, this is how it shows on SNAP

@dsmilo I use the same subswath (which is IW2) and use S1 TOPS Coregistration and the modeled coherence showed as:

I did use the exact dataset mentioned in the paper and he SNAP was mentioned as his tools. Screenshot from his paper as:

That’s why I don’t know why he was able to create a very good interferogram and mine shows grainy results. I can’t figure out what i missed doing

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If some can try here is the link of the downloaded Sentinel files.

https://drive.google.com/drive/folders/0B3if9bjQvNR8WThmNmFGQjdtY0E?usp=sharing

Hoping someone can show what process i miss or did wrong to come up with a good interferogram and subsidence map

Thank you all

@ABraun @dsmilo @johngan @smithalas @sharifulgeo

@mfoumelis is one of the authors of this document and also member of this forum. Maybe he can explain how these nice fringes were achieved.

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Yes i have see that @mfoumelis is one of the authors maybe you can help explain the process made that would really be a big help…

Thank you!

That scene has a lot of water in it, perhaps the ESD-correction did not work properly?

this is what I achieved with this data and the given processing steps:

Yes, highly recommend reaching out to the authors directly to see where you are falling short. I am eager to see what was done to accomplish the results shown in the paper.

It does look like a subset was applied by looking at the report result boundaries, however.

Yes I would be eager and excited as well to know what was done on the process to achieve the results shown on the paper…and it would help as well to note in future processing of insar

I hope @mfoumelis can help us on this

@dsmilo where in the process should subset be done if using TOPSAR data? i think it can be done after interferogram formation and debursting am i right?

@ABraun well yours still show bigger fringes than mine. Mine looks grainy rainbow coloured in all images

I filtered and multi-looked as described in the report.

Check out this tutorial to help get you started:

http://step.esa.int/main/doc/tutorials/

This should be your first step. Then coregister…ect…

If you perform a subset after coregistration or even interferogram, you are essentially clipping or cropping the image to make it smaller, not really performing a true subset.

However,after coregistration(Radar>Coregistration >S1 TOPS Coregistration with ESD),it has stacked into a single file,how can I run stack overview?Thanks

If you have multiple single files, you use the InSAR Stack Overview from the menu (Radar > Interferometric > InSAR Stack Overview)

If you have already coregistered them, you can load the InSAR Stack tool grafik (under View > Tool Windows > Radar > InSAR Stack)
The single tabs will show you the baseline information as well.
grafik

Thanks a lot ,here are more question:what’s the differnece between the menu of coregistaton>Stack Tools>Create Stack and Interferometric > InSAR Stack Overview ,which is both sub-menu of Radar in SNAP7.0? :grinning:

create stack is for geocoded rasters, coregistration is for SAR products in slant range geometry

so late for thanks to you,now I’m interesting in PSI of how to pickup the unusuall shift trend of PS candidates and ingoring normal PS candidates ,then visualize them,Could you give me more suggestions ?

could you please explain a bit more what you mean by “pickup the unusual shift of PS candidates and ignoring normal PS candidates”?