Surface Subsidence

[M.Ali512]

Hi Everyone,

I Want to monitor the surface subsidence of my specific study area from year 1990 to 2015 with “SAR Interferometry”
so my question is that is any satellite which provide data in this range of Time…??
or can I use 2 different satellite data for SAR Interferometry…??
Like RadarSAT 1 and RadarSAT 2

Plz Help

[lveci]

There were no SAR satellites in 1990. ERS-1 starts from 1991, RS1 starts in 1995 and even then you probably won’t find acquisitions everywhere unless it’s a supersite like Mt Etna.

[M.Ali512]

Thanks @lveci for Reply
Need Your More Help
Is It Possible To Use RADARSAT 1 Data for SAR Interferometry…??

[ABraun]

technically yes. But the repeat cycles are usually quite long (24 days) which leads to temporal decorrelation, especially due to the wavelength of the c-band:

Some explanations about concepts of fringes of interferogram and coherence

Atmospheric phase cannot be removed by a SNAP module as it cannot be modeled, like flat earth phase or topographic phase, for example. If you would make reference measurements of water vapor or have dense time-series data (example) you could theoretically remove the atmospherical phase distortions. This is advanced however (example 2). You calculate an interferogram between a pair of images. It shows you the differences between both images regarding their single phase signal. As the satelli…

Subsidence map in 3d view

thank you, @heinzollerketchup. Generally, the longer the temporal baseline (=the time between two images) the higher is the decorrelation which leads to small coherence values. It also depends on the cover of the analyzed surface. Bare ground mostly shows slower decorrelation than one with high vegetation cover. As you can see here (tested with S1 data), coherence decreases from 0.7 to nearly 0.1 within 6 12-day-cycles (12, 24, 36, 48, 60 and 72 days, blue to red) [image] Source: http://ieee…

[john_chamber]

Hello,

I am currently working on surface subsidence using a stack of SENTINEL-1 images. I understand that the more images we stack, the more the atmospheric error is minimized.

So, my question is:
Lets say i have five images, perform the interferometric processing (pair1-pair2, pair2-pair3, pair3-pair4,pair4-pair5) and create a stack out of them. pair1-pair2 form the subsidence map1, pair2-pair3 form the subsidence map2, pair3-pair4 form the subsidence map3 and pair4-pair5 form the subsidence map4. Finally, i add them all up ( subsidence map1 + subsidence map2 + subsidence map3 + subsidence map4) to find the final displacement map. At the very end, i want to discard pixels values that have coherence value below 0.5.

So, do we just choose a random coherence layer out of the 5 pairs to masks out the low coherence values?.
Do we add up the coherence layers as we did for the subsidence map?
Do we multiply each coherence layer and the we mask it out?

What method is recommended to follow?

[ABraun]

I can think of two options here:

1. Calculate an average coherence with the band maths and apply one threshold (0.5 seems too high for a mean value because the raster values will generally be lower after the averaging and not many areas will remain. Maybe 0.3)
2. Apply a threshold of 0.3 for every coherence image to get 5 binary masks. You then multiply all masks and have values of 1 remaining at pixels which were above 0.3 at all times and 0 where coherence fell below the threshold at least once.

[john_chamber]

thanks for your reply,

I forgot to ask about multilooking. Many suggest that multilooking improves the quality of the image? does it make the SAR image smoother?

Do you recommend multilooking as an important step? if yes, do we do multilooking at the very end of the InSAR process?

thanks

[ABraun]

multi-looking can improve the image/interferogram quality, but inevitably reduces the resolution. So if you don’t depend on the resolution of 10 meters of S1 you can perform it, but it is not required at all.

[demevengderrick]

hello everyone,
talking of the multi looking, i remarked that the resultant displacement obtained with a multi looked interferogram is different from that without multi looking the interferogram. is it due to the reduction of the resolution as said by @ABraun or something else. also which is more reliable, with or without the multi looking?

my second question is how do i add a stable point in my displacement map. following the tutorial from ESA, when i take the pixel value and add to the displacement map, it affects the lower but also the upper bound of the displacement histogram. i looks strange to me, is there a proper way to do it?

thanks.

[Pankaj_2806]

hi all,
I am trying to find out subsidence in a particular area. I am using sentinel-1 data set for that and till now I have done

1. Coregistration 2. Interferogram generation 3. Deburst 4. Topographic phase removal 5. Goldstein phase filtering
2. Snaphu Export 7. snaphu Import 8. Terrain correction now what should I do for further processing(what step I should follow) and finding the Subsidence of particular area?

[ABraun]

Please follow this topic Subsidence map in 3d view
It starts exactly at your step.

[ctheodor]

@john_chamber can you be more specific on the stack processing?

[suribabu]

Hi John,
I’m using around 10 images for Subsidence studies,I updated orbital file and TopSAR-split, please tell me how to run batchprocessing for these ten images(1-2image, 2-3 image , 3-4 image and so on).
And then how to add these output to a single image ?
please clarify this doubt…

Thanks
Suribabu

[ABraun]

currently, SNAP only allows single master interferometry (1-2, 1-3, 1-4).

[suribabu]

Thank you so much ABraun.
Please tell me how can i add these (1-2, 1-3, 1-4 ) SAR interferometric images to a single image (single output).
Means how can i add these images (1-2, 1-3 and 1-4) to a single image.

[suribabu]

Please suggest me which method is more beneficial for subsidence studies in urban areas. (1-2, 1-3, 1-4 …etc) and (1-2, 2-3, 3-4…). based on that I will do manually.

[ABraun]

have you seen the subsidence tutorial? Sentinel-1 TOPS interferometry
The last section gives a suggestion on how to combine images of multiple dates.

[suribabu]

Thank you ABraun…

[suribabu]

Dear ABraun
I followed the above tutorial (Sentinel-1 TOPS inferferometry) steps and created this below displacement chart from 2017-2020. shown in below figures.

I stacked all the 12 displacement images(1master+11slave). and then Using Band Math i created one displacement_combine ((1+2+3+…12) / 12). then
how can i create profile plot from 2017-2020 displacement ?
and please tell + and - values indication in google earth map (means which part is uplifting or subsiding) ?

[ABraun]

first you digitize a line, then you select the profile-plot tool

• means movement tpwards the sensor and - away from the sensor in line-of-sight.