How to know subsidence or uplift from the pixel signs

farmanghaleb · January 31, 2019, 9:25am

Hi,

I have created a displacement map from two pairs of Descending SAR images for an AOI. I have single pixel gives the amount of displacement with minus or plus sign.
I do not have any stable reference point from GNSS instrument in the AOI at present time, but I only know some areas have not been moved or displaced. I chose a point from that area and subtracted from the whole phase map.
In this case, without visiting the site, how I know the area of subsidence from uplift?
Many thanks in advance

falahfakhri · January 31, 2019, 10:39am

Have a look at this, I think it is helpful to understand better your question,

farmanghaleb · January 31, 2019, 10:42am

Many thanks for your reply on my question.

I’ll have a look and let you know if I wanna more information about it

cheers, Farman

farmanghaleb · January 31, 2019, 11:11am

Dear Falah,

I have been exploring the RUS services for a while but I think it is not available for people who live outside of the EU countries as states down

Access to the RUS service is currently suspended to persons outside the European Union .

Any comment, please? Am I right? Thanks

falahfakhri · January 31, 2019, 11:29am

Yes, that is right,

But, I think the webinar and the youtube channel are available for all around the world, so you could exploit this benefits.

farmanghaleb · January 31, 2019, 11:31am

Thanks for confirming that… Hopefully in the future

Cheers, Farman

farmanghaleb · January 31, 2019, 11:41am

Dear Fakhir,
SO what is your opinion on my very beginning question, as states down

Thanks

falahfakhri · January 31, 2019, 11:51am

Have a look at this place,

farmanghaleb · January 31, 2019, 12:18pm

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

falahfakhri · January 31, 2019, 12:30pm

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/

farmanghaleb · January 31, 2019, 12:38pm

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

falahfakhri · January 31, 2019, 12:51pm

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

ABraun · January 31, 2019, 2:01pm

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

falahfakhri · January 31, 2019, 2:21pm

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.

farmanghaleb · February 1, 2019, 2:06pm

[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

falahfakhri · February 1, 2019, 2:12pm

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,

farmanghaleb · February 1, 2019, 2:19pm

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

falahfakhri · February 1, 2019, 2:21pm

Did you take a look at the edited post,

farmanghaleb · February 1, 2019, 2:23pm

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!

falahfakhri · February 1, 2019, 2:29pm

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.