Subsidence map in 3d view

Ops…I modified it now…I mean for example, the glacier height should be between 10 to 1000 meter (almost) but now by this method, it is not.
Yes, ramp is removed but results are not correct.

I think that is because the trend includes the absolute heights. If you remove it, you end up with an average height of 0 (as shown in the last plot). Instead, you have to calculate a difference between a reference height (e.g. Copernicus DEM) and your TanDEM-X elevations, extract the trend of this difference and remove it. Then, what remains should be close to the reference heights.

Dear @ABraun . Thanks for reply.
I did what you suggested me but it did not work. The reason is my AOI is glacier, so one side (accumulation area) is upper than another side (ablation area). So, even over Copernicus DEM, we still have this trend.
The below result is average of every column for TanDEM-X DEM, Copernicus DEM and you can find their difference with yellow color.

I added DEM result and Copernicus DEM images here as will.

Figure 1. TanDEM-X dem


Figure 2. Copernicus dem

Then the East-West trend is not fully representing the faulty orientation of your TanDEM-X DEM.
Another option is to extract the differences at multiple points in the image and create an interpolated difference map. This can then be subtracted from the DEM.
We did this in our study in Vietnam: https://doi.org/10.1080/22797254.2019.1604083

I do appreciate your effort. However, shouldn’t this entry be applied to the resulted displacement image from step 1?

My comment is older than 5 years - so things might have changed in the meanwhile :slight_smile:
I think it strongly depends on what your data looks like, what you need and when you do the masking. Plesae check this discussion here:

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I understand. I still notice a debate which is quite interesting, I am waiting for Berno to show us his results.

Although what genuinely confused me is that masking out low coherence would have been done to the unwrapped phase image before creating the displacement image, so that when we create the displacement image from the edited uwp. image, we would be able see the effect of removing low coherence on the displacement values.
Then from the latter we determine what the “x” value is, where there’s no surface changes expected, substract “x” from the uwp. image and then re-create the displacement map after the changes. Or simply substract that x value from the displacement image created earlier.

Could you point out what the roughly phase ramp looks like? I have already searched this term in “Guidelines for SAR Interferometry Processing and Interpretation” but I couldn’t find clues. I’ve found this material
(PDF) Slope deformation prior to Zhouqu, China landslide from InSAR time series analysis, however the ramp they have mentioned is quite different to what you have commented at.

It does not affect the result if the masking is done to the unwrapped phase or the displacement image. This only removes areas with insecure patterns (e.g. if you have local peaks and don’t know if these come from atmosphere or actual displacement)
It does affect the result when you mask out low coherence areas before unwrapping. But it depends on the size and distribution of these areas and their fraction of the overall image.

Yes, the ramps in the study you mentioned are highly systematic and determined by bad orbit quality, false flat-earth estimation, ionospheric patterns…
What I meant in terms of ramps caused by unwrapping of noisy phase is shown here, for example:

grafik
Souce: Displacement from Sentinel1 - #35 by chronomanz
As you see, none of the unwrapped patterns relate to actual displacement. They are a result of the random phase in the interferogram which sums up during the unwrapping in unexpectable directions. Using such results would not be credible.
More examples on ramps here: Phase unwrapping and low coherence - #2 by ABraun

I read this paper but it did not mention to the ramp directly. I think it can be found in this paragraph:

Derivation of surface heights and built-up areas?

Actually it is not clear to me that where was the ramp in this work and which method you used.

Anyway I did what you suggested me (although I thought this would not work):

I divided all columns in nine columns and I selected 3 points on any of them (1 in below figure), then I got average from them (2 in below figure) and made a fitting line on them and continue as previous approach but as you can see results are not real (4 in below figure)….

Sorry for the misunderstanding. Instead of averages per column I was talking of a trend surface to be subtracted from the TanDEM-X DEM. The part in the study is “Vertical adjustment of both images”

This may be a primitive question but If I may ask,
is there a difference in meaning between “Phase jump” and phase “ramp” terminologies? I understand that path following-phase unwrapping process can be erroneous if phase jumps occur when the interferogram fringes are distorted by discontinuities resulted from cases such as layover or the presence of water bodies. I couldn’t find descriptions for such terminologies in Ferretti’s guide (InSAR Principles: Guidelines for SAR Interferometry Processing and Interpretation) So, if possible, can you highlight those phenomena in the figure provided by the author of this post under discussion

With phase jump I mean strong changes within two pixels, e.g. caused by height changes above the wavelength scale (5 cm for Sentinel-1).
With phase ramp I mean the overall trend superimposing the fringes which is often introduced after unwrapping.

I’m not sure if these are scientifically legit.

If you have worked with StaMPS before, in step 7, the spatially correlated DEM error is calculated and additionally the phase ramp is calculated when setting the parameter “scla_deramo, y”, how would the phase ramp that may have been introduced during the unwrapping affect the estimated mean LOS displacement velocity?

PS analysis is less prone to unwrapping errors because it constructs a network of stable scatterers. The mentioned ramp is a bigger problem for traditional raster based DInSAR where large parts of phase noise are unwrapped.

I had (stamps_tsexport.csv) and I want to calculate vertical displacement or subsidence from relation :
image
How can I do this please help and thank you in advance

I had (stamps_tsexport.csv) and I want to calculate vertical displacement or subsidence from relation :
image
Based on the reference( Monitoring of long-term land subsidence from 2003 to 2017 in coastal area of Semarang, Indonesia by SBAS DInSAR analyses using Envisat-ASAR, ALOS-PALSAR, and Sentinel-1A SAR data)
How can I do this using snsp or what ? please help and thank you in advance

This equation is not very precise, but an approximation of actual displacement.
I don’t know how do implement it in Matlab (would probably be the easiest way), but if you have already exported it to CSV, you can load it into a GIS (e.g. QGIS) together with a raster of the local incidence angle (exported from SNAP) and extract the angles to each PS point. In the attribute table of the points you could then apply the equation based on both variables.

I explained how to load the CSV into QGIS here: StaMPS-Visualizer, SNAP-StaMPS Workflow - #315 by ABraun

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hello ABraun … I want to calculate vertical displacement …Please help me understand this relationship. Is it intended that I always replace LOS displacement with a positive value even if it is negative?

Based on the reference( Monitoring of long-term land subsidence from 2003 to 2017 in coastal area of Semarang, Indonesia by SBAS DInSAR analyses using Envisat-ASAR, ALOS-PALSAR, and Sentinel-1A SAR data)
Thank you dear in advance

hello ABraun … I want to calculate vertical displacement …Please help me understand this relationship. Is it intended that I always replace LOS displacement with a positive value even if it is negative?

Based on the reference( Monitoring of long-term land subsidence from 2003 to 2017 in coastal area of Semarang, Indonesia by SBAS DInSAR analyses using Envisat-ASAR, ALOS-PALSAR, and Sentinel-1A SAR data)
Thank you dear in advance

I had (vs-do)

does this mean that there is wrongs in my results… because when I calculate vertical displacements I have errors in the edges

please help