# How to know subsidence or uplift from the pixel signs

Thanks for your swift reply, I have read this post before, but how I know the displacement going towards the sensor or getting far from it ? If I know that I know how to judge but in my case firstly, I don’t have any ground observation from GNSS device and I have not been to the AOT. Secondly, I only have displacement value with sign (+ or -). for example, the phase pixel reads (-0.05 m) and in another pixel reads (+0.07m)…

Can you comment on this please? thanks

In case of (-) value that’s mean the movement away from satellite and it refers to subsidence,
in case of (+) value that’s mean the movement towards the satellite and it refers to uplift.

Be careful of using these terms, For instance Displacement, Deformation average, and so on,

I found for you a very nice explanation you could read it,

https://skygeo.com/insar-technical-background/

so sorry to terrible you dear Fakhir… I will be going through your link that you sent already…

But I think (pardon me) In case of (-) value that’s mean the movement get close to the satellite and it refers to uplift and vise versa, correct? thanks

NO, the right answer I explained to you in the previous post.

it always refers to the master image. So in case the master image is the second date, it can be switched.

But this is not the case, despite of the master image, generally suppose that the ground on the zero level any movement towards S. It is uplif and away it is subsidence, this is closest to the fact as well,

It could be calculated in to two ways,
The first way as I explained, So - means subsidence and + means uplif,
The opposite way is , the ground movement calculates according of it distance from satellite, in this case away from satellite it is subsidence and it has + sign , towards satellites it is uplif and it has - sign.

[quote=“falahfakhri, post:14, topic:13767”]

Dear Fakhri, Thanks for your reply back on me.
Does your first way apply on my case or not as I am almost lost to judge on my LOS displacement map. I have attached a screenshot of my AOI with LOS displacement map and I put the a small area in a red circle with its value on the left hand side of the screenshot.

Thanks

I think the area is close to the Darbandikhan DAM, if that is right? So this area is subjected to subsidence, now, I’d like you to tell me, what is your guess about this number?

Have a look at this could help you, because this work has been done close to your study area,

Good to know about the incident!

The engineering staff claims a subsidence of 60 cm by GNSS techniques, however, the SAR interferometry shows only a few cm(s) downlift (in my opinion). I am so confused, I think it is subsidence but not sure in the meantime!

Look forward for your opinion

Did you take a look at the edited post,

I read that paper, it is so complicated in terms of processing and it does not show a relevant to GNSS data that the Dam staff gave it to me!

The important thing to you from my point of view is, this area is subjected to the subsidence in ultimately this sign - refers to subsidence, the second thing is, I don’t know what kind of approach do you follow? and what is the goal of your study?

So identify the approach and the goal of your study and therefore, choose the technique you’d like to implement.

The differences of tools and date and method could give a different in the measurement results, that is all what I could say, because I haven’t clue to the details of your study.

Dear Fakhri, thanks again for your reply… I want to measure the LOS displacement (subsidence and uplift) in the AOI. and also compare it with GNSS data of the same area. The first result was from two Ascending SAR images with temporal baseline of 24 days. However, I wanna validate the results by using tow Descending SAR data as well but with temporal baseline of 6 days and 62 m Perpendicular baseline. so, if I get the a similar result to the Ascending one, it gives me a confidence about my work even it does not come right with the GNSS data!
I will process the second data and inform you with the new results…
Many Thanks for you and ABraun

Hi the learned,
Please, I would like to know the final resolution on this matter because I am also trapped in a similar corner.
Kind regards.

hello, when I convert the interferometric phase to displacement ,Ihave displacements

but when I use the Range Doppler Terrain Correction operator to terrain correction the displacement is zero

what is meaning this?
thank you in advance.

Please update SNAP (bottom right corner) and try again. Furthermore, use SRTM 1Sec (Auto Download) instead.

thank you for kind reply

did this solve your problem?

yes it solved my proplem.please ihave another quistion .
the coregistration for other tow images(26-11-2018,20-12-2018)s1 iw-slc-ascending is blue although I used 4bursts and srtm1sec as you told me at last time.
what is the reason?
thank you for help me dear ABraun

have you applied SPLIT to the correct bursts? Sometimes two products of the same relative orbit are shifted along track. You can check if they cover the same area after the splitting in the WorldView window.