TopSAR Processing

[Serasia]

I’m sorry but I had not seen your question.
I’m working on a new project where we have to found the vertical displacement of the surface.
I have looked for info and manual on the web and I have followed all the steps found on the user manual of the Interferometry tutorial of ESA that coincide with what I have found on this forum.
So, I have used SNAP and SNAPHU like ESA suggests.
When I have finished to processa an area, I was not sure that my results were correct because I have not a feedback so I have repeated the same process in an area where I know that a street dropped down in Rome for -10m.
So I have used two S1_SLC images where the master was before the fact and the slave, after.
But, as I said before, the results are completly different.

[mengdahl]

When I have finished to processa an area, I was not sure that my results were correct because I have not a feedback so I have repeated the same process in an area where I know that a street dropped down in Rome for -10m.

That disturbs the scatterers completely, plus the movement is so large that it would anyway be impossible to tell how many multiples of the wavelength the surface moved. So this is not going to work - you could try to detect precursors of the collapse (if any) by doing PSI-processing with SNAP+StaMPS.

[Serasia]

Yes thanks.
I have already been advised to use Stamps.
My problem is that it was months that I was trying to get this result and now I realize that I have to use another very complex method that will make me lose a lot of time that I do not have.
Also because others in the forum have sent me some documentation to study but very theoretical, but I have not found any guide telling me step by step what to do to get the vertical dislacement with snap and stamps.
I would need one like the one I found ESA in which it explains in detail the steps to follow on snap, how to install snaphu and how to get out snaphu.
Can you help me on this?
I also asked if there are courses on the subject but at the moment there are no online and the first profit is in September.
I would need a manual like the one I said or someone to give me lessons on how to proceed.

[ryeramirez]

choose a pixel as reference point from terrain corrected product (with high coherence in time prefered) and check pixel value.
Next step: create a new band go to band maths (deformation band - reference point pixel value). This is the final deformation map.
Next you can create a coherence mask. Stack the final terrain corrected deformation map and terrain corrected coherence band. Create a new band to mask the coherence. Band math (e.x. If coherence band > 0.4 then 1 else NaN). You will have a new coherence mask band.
Final step: create one more new band. Band maths ( final terrain corrected defo band * coherence mask band).
This will be your final product.

Hi, vasilisgeo88!

I am new and just getting started with InSAR, and somehow managed to finish each step up to Range-Doppler Terrain Correction. I am interested in producing a final deformation map and came across in this forum specifically with your reply to @Serasia. I am a bit puzzled actually on how to do it step-by-step, starting from choosing a pixel (with high coherence) as a reference point to creating a new band to creating a coherence mask and so on. Do you have a video tutorial and/or tutorial on paper on how to do it exactly?

I hope you can help. I really appreciate all the discussions here.

Thank you.

[ryeramirez]

choose a pixel as reference point from terrain corrected product (with high coherence in time prefered) and check pixel value.
Next step: create a new band go to band maths (deformation band - reference point pixel value). This is the final deformation map.
Next you can create a coherence mask. Stack the final terrain corrected deformation map and terrain corrected coherence band. Create a new band to mask the coherence. Band math (e.x. If coherence band > 0.4 then 1 else NaN). You will have a new coherence mask band.
Final step: create one more new band. Band maths ( final terrain corrected defo band * coherence mask band).
This will be your final product.

p.s Don’t forget the the first basic step to apply orbit file.

Hi, @falahfakhri! I’ve came across this post by @vasilisgeo88. I’ve done (deformation band - reference point pixel value) and created a new band as shown below:

(Final deformation map)

I am not sure on the next step mentioned. “Next you can create a coherence mask. Stack the final terrain corrected deformation map and terrain corrected coherence band. And so on…” I couldn’t figure out how to do it.

I hope you can provide me a guide. Thank you.

[falahfakhri]

I’d like to start from the reference point step, I think this is different to what you are looking for, Or what is the goal behind the selection of reference point.

In here our colleague has selected a high coherent pixel and then according to the value of coherence result, he considered as a reference threshold of the coherence and hence of the deformation.

I couldn’t figure out how to do it.

This is easy to apply, once you have created the coherence product, you could open the band math, and apply the following statement condition to create the mask, for example,

IF coherence >= 0.35 Then 1 ELSE 0

The result of aforementioned statement is a mask of only the coherence = 0.35 and higher , the other will be 0, this mask named coherence multiply by the original coherence map, will result only an interferogram of the selected coherence,

Please keep in mind, there is a difference between what is mentioned in this post and the reality behind the selection of the reference point.

An important thing it is worth mentioning here to give you an entire answer concerning the reference point, Please take a look at the following post,

Subsidence map in 3d view

Assuming that your unwrapped phase is “Unwrapped Phase_ifg_srd_VV_05Dec2008_24Apr2009” and your reference height is 15: Right-click on your unwrapped phase open Band maths and enter Unwrapped Phase_ifg_srd_VV_05Dec2008_24Apr2009 - 15 If the measured value is negative, add it instead.

[ryeramirez]

Hi, falahfakhri!

Thank you for the explanation, but I am still confused. Is there a way I can communicate with you ‘verbally’?

If it’s not possible, I will make a flowchart to show you the steps I am following and please comment if where do I do/insert the additional steps you’ve mentioned.

Thank you, and my apologies for my ignorance.

[gomalhunzai]

@ryeramirez i was also confused about this step, what i understand from reading posts realted to deformation is that , we have to select a point which u think is not chnaged throughout the time span of your study. you can also get this value if someone has GNSS or leveling data of your study area. By comparing the data you can validate your results.

[falahfakhri]

Hi,

No problem, we are learning from each other, Please don’t hesitate to add your flowchart, in this case the benefits comeback to all.

[ryeramirez]

Hi, falahfakhri!

I’ve uploaded here the following figures:

1. SNAP Workflow
2. Screenshot of my Product Explorer Panel
3. and some clarifications on the post of @vasilisgeo88

I hope you can enlighten me on these things.

Thank you!

Figure 1. SNAP Workflow

Figure 2. Product Explorer Panel Screenshot

Figure 3. Clarifications on what to do with the post of vasilisgeo88

[falahfakhri]

Please take a look at this steps in this post,

Phase to elevation - BLACK product

I think this post is quite good start for you, also remember the criteria of SAR IMAGES before to go a head in the processing for example the perpendicular baseline is a key point of created the elevation map, Also, please have a look at this, [image] [image] Source I think it is very nice tutorial, but let’s do it easy, 1- Split, Select where is your AOI in which subswath IW1-IW2-IW3, 2- Apply orbit, 3- Back geocoding 4- Apply ESD 5- Create an Interfogram 6- Deburst 7- Goldenstei…

However, in your case step 9 is as below,

And step 10 is phase to displacement instead of what is mentioned in here,

Concerning the reference point, I think it well discussed in this post,

Difference between vertical and LOS displacement

@ABraun can you please tell me why we have to add the reference point value and vertical displacemnt, in INSAR tutorial by Dr.-Ing. Diana Walter. Also, does the sign of the reference value is important or not??? [Screenshot_4]

[ryeramirez]

Figure 3. Clarifications on what to do with the post of vasilisgeo88

@falahfakhri, thank you for sharing those posts. I will go through the threads. Have you considered checking Figure 3 which I uploaded yesterday? For the displacement product, how do I mask those pixels with incoherent values? Could you please check Figure 3 and tell me if I understood properly the instructions by @vasilisgeo88. Thank you.

[ryeramirez]

Thank you for the idea. What I did after obtaining a displacement product after applying terrain corrections was this:

1. In my coherence band where I also applied terrain correction, I masked the pixels with coherence less than 0.90. I right-clicked on the band —> Properties —> Valid Pixel Expression (Coherence Band Name > 0.9). After doing so, I noted the information about the pixel with somehow the highest coherence specifically its position.
2. In my terrain corrected displacement product, I looked for that pixel with high coherence and noted the value of displacement. Then I created a new band following these steps —> Raster —> Band Maths —> (New Band Name) and made the following expression (New Band Name - Pixel displacement value with high coherence).

I do not know if what I did are all correct. I am trying to understand and do what vasilisgeo88 mentioned in one of his posts.

Please take a look of what I am following in my study. I hope we can share ideas. @falahfakhri is also helping me and I am very thankful to him.

[ryeramirez]

Hi! I was looking for the graph showing the effect of temporal baseline on coherence in one of the fora here but unfortunately, I couldn’t find it anymore. Can you please provide me the graph and some relevant papers discussing the effects of temporal baseline and perpendicular baseline in coherence estimation? Thank you.

[falahfakhri]

the effect of temporal baseline on coherence

In general the long temporal baseline in vegetated area, or unstable objects within same area affects the coherence correlation between two or more passes,

This matter is discussed here,

DEM creation

and perpendicular baseline in coherence

Here also is good explanation

Sentinel 1 per. & temp. baseline

Some example of articles,

Impact of Perpendicular and Temporal Baseline Characteristics on InSAR Coherence Maps

The effect of the perpendicular baseline on coherence for SAR images in InSAR

Also it is explained well in here

Source

[ryeramirez]

Thank you, so much! I will go through it.

By the way, have you seen already my comments about vasilisgeo88 post? I am still waiting on your response regarding that.

[ryeramirez]

I also would like to ask if it is okay to stack 2 SAR images from different frames but from the same path and with the same polarizations. Thank you.

[ABraun]

I was looking for the graph showing the effect of temporal baseline on coherence in one of the fora here but unfortunately, I couldn’t find it anymore.

this one? Subsidence map in 3d view

[ryeramirez]

@ABraun, yes! Thank you so much! So basically, with regards to time and distance, the shorter the temporal baseline (days) and perpendicular baseline (meters) the better the coherence. Am I correct? I’ve read some papers while waiting for this graph and the findings are like that.

[ABraun]

This is true for the temporal baseline.
The perpendicular baseline is more indifferent. For example, for DEM generation, 150-300 meters are stated most suitable.

source: http://www.esa.int/About_Us/ESA_Publications/InSAR_Principles_Guidelines_for_SAR_Interferometry_Processing_and_Interpretation_br_ESA_TM-19