PSI is they way to go for measuring ground displacement but it requires many images acquired over the same area of interest (20-25). StaMPS (https://homepages.see.leeds.ac.uk/~earahoo/stamps/) is the most popular method for performing PSI analysis. It requires to have matlab installed in your PC though. Using SNAP, you can export your unwrapped phases into StaMPS format and perform PSI.
Based on your previous messages you are lack of basic knowledge about geodesy and vector algebra. If “only vertical displacement exist”, how can you guarantee in a geologic event that the ground just moves up or down, no slide? How can this kind of ridiculous assumption be adopted in engineering?
Please discuss with respect. You are free to disagree with anything stated here but don’t attack users at a personal level. Calling contributions of others who are genuinely trying to help you ‘ridiculous’ is not helping in any way. If you think different about discussed points, please bring up your arguments.
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Sorry about that! If you can please remove what I have posted. Thank you very much for the advice!
As I searched online the main steps and advantages of PSI are (a) it uses features of Permanent Scatterers found in images to improve the accuracy of co-registration for several images before interferometry; (b) the phase( or its difference ) computed by interferometry will have less errors; © it exploits a “2+1D phase unwrapping” using a set of redundant
interferogram result to compute the displacement.
In the Help of SNAP for PSI/SABS there is only 1 item described – “StaMPS Export”. In its description it looks SNAP have done both (a) and (b) above, and in your previous message that “you can export your unwrapped phases into StaMPS format and perform PSI.” If so, (1) In the result of SNAP exported to StaMPS, what is the criteria SNAP considers a feature in the image as a PS( Permanent Scatterer )? or where can I find a relative paper? (2) It looks SNAP’s “StaMPS Export” function exports wrapped phase, not un-wrapped phase, to StaMPS, because usually SNAP does not do un-wrapping, right?
Thank you for the help!
In order to perform PSI, the same procedure as InSAR is followed in terms of processing the data (TOPS co-registration, interferogram formation, deburst). Deformation can only be measured over available PS. High density of PS can be identified on building and roads (objects that do not change rapidly in time) while very low density of PS can be identified in vegetated areas.
For selection of PS , phase stability and amplitude dispersion are used.
StaMPS is by far the most popular method for performing PSI (I have never used it myself as i do not have licence for matlab).
What you need to do is to create interferograms for your area of interest, deburst and stuck them (elevation band is also required i think). Then you can export this file into StaMPS. If you need more information on this, you can visit the discussion in this forum about staMPS and PSI . How to prepare Sentinel-1 images stack for PSI/SBAS in SNAP 5
Below, you will find a PDF where it explains what command to run for performing PSI in StaMPS.
D4P2a_LTC2015_Hooper.pdf (1.1 MB)
I think you can look this up on sentinel 1’s official esa page under technical specs. (the site where they list all the hardware specs etc.) They also have the angle and swath length and stuff
I have observed it correspond to my own metadata in snap.
Hi @hchong005 ,
Yeah I found that also from metadata section. Thanks.
Is there any reference cited the below equation?
(unwrapped phase * wavelength) / (-4 * PI * rad(cos(incidence angle)))
http://www.esa.int/esapub/tm/tm19/TM-19_ptA.pdf54, chapter 2.3.
I have read your post and i have a questio for you.
If the vertical displacement is:
unwrapped phase * wavelength) / (-4 * PI * rad(cos(incidence angle)))
the horizontal displacement is:
unwrapped phase * wavelength) / (-4 * PI * rad(sin(incidence angle)))??
Please let me know.
Have a nice day
Good evening to everyone,
I’m new on this subject.
I was entrusted with a project that concerns the detection of the displacement of the land both horizontally and vertically.
I started to study the basics on Sentinel (different types of products, modes, etc.) and I downloaded SNAP.
I have read several guides and tutorials and thanks to your help I have obtained results.
I need to know if what I have done is correct and if I have finished with the steps or I need other operations to do before getting the final results.
The steps I have performed are the following:
1 I took from the copernicus hub two images of the same place at a distance of 12 days (S1A_SLC_IW).
2 I created this chart on SNAP and I ran it:
3 I exported the result to SNAPHU
4 I have performed unwrapping on SNAPHU
5 I imported the result on SNAP
6 Phase to displacement -> (unwrapped phase * wavelength) / (-4 * PI)
where according to my calculations the wavelenght is 0.055m
7 terrain correction
8 I have marked the value of displacement_Terrain Correction in a high coherence point (taken from the coherence band obtained by unwrapping)
9 terrain correction - pixel value
I then generated the vertical and the horizontal displacement like this:
(unwrapped phase * wavelength) / (-4 * PI * rad (cos (incidence angle)))
(unwrapped phase * wavelength) / (-4 * PI * rad (sin (incidence angle)))
12 I applied steps 7,8,9 for both vertical and horizontal displacement
After that I moved on coherence:
13 I performed the terrein correction of the product obtained from step 2
14 I created a math band with the following formula:
If coherence band> 0.4 then 1 else NaN
15 I created a stack respectively between the product obtained from step 14 and steps 9 and 12 (three different stacks one for the displacement one for the vertical and one for the horizontal)
16 I ran the maths bands
result step 14 * result step 9
result step 14 * result step 15 (two different operations)
What I did is correct?
I’m finished or do I have to take other steps? (I read on the forum that maybe I have to use STAMPS for PSI)?
How can I tell if the results are right or not?
please help me.
When doing measurements with SAR sensor to identify movements on the ground, we can resolve only one surface displacement vector. What the satellite measures is the distance between the satellite sensor and the ground but we cannot say that the ground was moved horizontally or vertically using only one satellite orbit (ascending or descending). If you want, we can make the assumption that the ground was moved vertically (we cannot be certain for that). SAR is much more sensitive to vertical changes rather than to horizontal ones. We need to combine ascending and descending orbits to resolve for the ‘true’ ground displacement.
Thank you for your answer.
I need to get the horizontal and vertical displacement of the ground.
So you’re telling me that to do this I need to process two images of the same point SLC-IW one with ascending step and one with descending step?
And if the images are more than two how do I do it?
Please let me know also because reading in this forum I read the various steps to follow (please tell me if the steps I did that I listed in the previous post are correct) but I never read that the images should be one ascendant and one descendent.
This means that I was wrong
Thanks for your help
Strictly speaking, to get the optimum results in intereforometry, the satellite orbits should be the same. The limitation of this is that only one surface displacement vector can be resolved. So, many studies carried out using both ascending and descending orbits to isolate vertical from horizontal motion. have a look on these articles.
You can collect a few images derived by both ascending and descending orbits and do the interferometric processing and see what you get.
Your graph looks correct
Thank you very much for you help.
I will let you know.
Have a nice week end.
do you know if are the te online courses on these topics?
not having basic knowledge I follow what I find in some tutorials or in this forum.
I would need to have some material available and take courses
For getting familiarised with SAR data you can check this online course:
in order to calculate the vertical displacement I used the following formula:
(unwrapped phase * wavelength) / (-4 * PI * rad (cos (incidence angle)))
I got the incidence angle from “show tie point grid” inside math band when I applied the formula.
Is it correct?
If yes, can you tell me how can I know the numerical value of this angle in order to apply the formula without that snap automatically taking it?
I’m using S1A_SLC_IW images
I also need some advice from you.
I would like to buy sensors to interface with Arduino in order to have a comparison with the displacement obtained with SNAP.
Can any of you advise me one?