How to know subsidence or uplift from the pixel signs

[Ikuemonisan]

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.

[SHAM]

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?
please help me
thank you in advance.

[ABraun]

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

[SHAM]

thank you for kind reply

[ABraun]

did this solve your problem?

[SHAM]

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

[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.

[SHAM]

I tried and checked . they covered the same area but the coregistration still blue.Idont know what is the solution . please help me

[ABraun]

this can be simply a matter of color scaling. As long as there is information from both the master and the slave (I see blue, white and red) it should be fine. Zoom in to check if the images are aligned.
It would only be a problem if the RGB would be entirely monochromatic (only one color).

[SHAM]

Thank you very much for your constant help and for finding solutions to my problems.

[survivere13]

hi, I just wanna make sure if I understood this right
if I have a pair of ascending images and my master is 2020 and slave is 2016, (-) means in the slave image we had movements toward the satellite so the distance decreased and we had subsidence in 2020, if any values are (+) it means that we had uplift in the area. am I right?

[ABraun]

this is my interpretation, yes.

But I am a bit concerned about the fact that you take an image pair with 4 years of temporal baseline. Does the interferogram still look alright?

[survivere13]

these are the outputs of interferogram
Phase_ifg_IW2_VV_21Aug2020_20Apr2016.bmp (2.2 MB)
phase
coh_IW2_VV_21Aug2020_20Apr2016.bmp (2.2 MB)
coh

[ABraun]

I’m afraid this is completely noisy - no chance to retrieve reliable information from such an interferogram.

A typical interferogram should look rather like this.

[survivere13]

thank you @ABraun
should I make interferograms like 1-2 2-3 3-4? I was willing to do the whole process with a single master, I’m afraid it’s not possible now

[ABraun]

yes, short temporal baselines help to maintain good phase quality

[survivere13]

alright thanks.
what should I do if I want to use this images for PSI processing? repaet al the steps for each pair?!

[ABraun]

PS processing requires a slightly different preprocessing. It is all summarized here: StaMPS - Detailled instructions

[Shadi1]

@falahfakhri

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.

I am really confused. According to this
https://vldb.gsi.go.jp/sokuchi/sar/mechanism/interpretation-e.html
The -ve sign means movement of the ground towards the satellite while +ve sign means the reverse (regarding the wrapped interferogram). So what do the signs of the values in LOS displacement and vertical displacement images really mean ?

[falahfakhri]

@Shadi1

I am really confused. According to this
https://vldb.gsi.go.jp/sokuchi/sar/mechanism/interpretation-e.html

Did you ask yourself, which software has been used!!!

@falahfakhri

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.

I think my above simple clarification already explains your question;

Once more, Do you use GAMMA S/W, or/and SNAP-StAMPS, then the right sign of subsidence and uplift is also has mentioned before is below once again,

@falahfakhri

generally suppose that the ground on the zero level any movement towards S. It is uplift and away it is subsidence, this is closest to the fact as well,

@falahfakhri

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.

Finally I have a message to all InSAR software engineers, in any next ESA related conference, hope to unify the subsidence, and uplift palette, Or ground movement representative palette.

For more clarification, because might be the junior researchers in some probability cases would understand the palette means the colors of the bar and the signs positive and negative, and actually Not, the following example explains more what I meant exactly of this phrase mentioned above with regard to unify the palette,

The core of InSAR techniques is measuring the distance between satellite and the objects on the ground or/and the ground, Let’s suppose the ground in the level zero, GAMMA S/W, and SNAP-StaMPS, calculate any movement towards satellite as an uplift and this represents an increase of the ground height from level zero, thus the sign is positive, on the contrary side any movement away from satellite means subsidence and ultimately it represents as a decrease of the ground height from the level zero and thus the sign is negative.

Other InSAR softwares, calculate the movement towards satellite or an uplift as a decrease of the distance between the ground or/and an object and the satellite, and then it has a negative sign, on the other hand the movement of the ground away from satellite or subsidence will increase the distance between both, and then it has positive sign.

Of course both are correct, unify the mathematical calculations of all software, and ultimately the palette will give the users and the clients of any company a good comprehensive idea of the actual process.