SNAPHU Unwrapping

Microwave Toolbox Interferometry
#281

thank you sir
these result showing relative height and displacement
how i will get absolute height and displacement (steps in software)?
I know the concept mentioned above that i have to give value to a point in map
but how ?

#282

technically, you just use the “phase to elevation” module which uses a DEM as auxiliary informaiton to make absolute values. But influence of atmosphere, low quality areas in the interferogram and processing errors during the unwrapping add up to unrealistic results. The only option is to use different image pairs and compare.
The temporal baseline is just too high, I guess.

#283

Images i used were of 14 and 26 jan 2018
So I think temporal baseline is correct ?
but again thank you for such a fast replies
now I will try on different data sets .
one last question you said these are the best possible result for that reason , why ?

#284

yes, only same path acquisitions. INSAR / DINSAR - Perpendicular baseline calculation

#285

Whether the sentinel-1 data is suitable for topographical studies?
Can building / feature height estimation be done by using this data?
Thanks

#286

The spatial resolution of Sentinel-1 is not high enough for building heights.

Here is an example where elevation was successfully retrieved from Sentinel-1: The Order of DEM Creating Steps

But in many other cases, atmospheric conditions, low coherence and unsuitable perpendicular baselines are hindering good results.

#287

image
image.jpg531×542 215 KB

Hey all,
I know this probably isn’t a simple question but can anyone guide me to the potential errors illustrated here…
This is an XXXX_split_Orb_Stack_Ifg_Deb_ML_Flt_unwrapped - phase-to-displacement product (range -0.211m to 0.174m) and I have masked out the low coherence (<0.3).
Are the two extremes in this image likely to be caused from unwrapping errors, atmospheric or could it be DEM?
Any assistance would be greatly appreciated.
Kind regards,
JB

#288

where do you see extremes and what is the value range between blue and red?

#289

The blue is 0.174m and the red is -0.211. It is these two regions I am referring to.
Is it just a matter of ‘localising’ in these areas?

#290

image
image.jpg1920×1080 569 KB

while trying to unwrap the phase, this is what i am getting (as highlighted). what do i do?

#291

you missed the number of lines at the end

See here: https://www.youtube.com/watch?v=sH4Uhsgmpak from 1:50

#292

Could you please tell me the purpose behind removing the topographic phase?

#293

The topographic phase is useful if you are generating a DEM but otherwise it should be removed so that it does not mask other signals of interest (deformation, coherence etc.).

#294

answer in another post

for the future please avoid duplication of your questions

#295

Hello
I have doubts about the process to convert the unwrapping phase to terrain displacement, could you please guide me?

#296

please describe more specifically, what data you are using, how you preprocessed it and at which step you struggle.

#297

Good afternoon,
My project is to determine the deformation of Galeras volcano (located in Colombia), at this time I followed the entire tutorial “Installation SNAPHU in Windows”, and I have the phases of the pairs of images to be treated.
and there are born my multiple doubts:

  1. the unwrapping phase has units of measurement? If the answer is yes, what is the unit of measurement?
  2. I have a formula to convert the unwrapped phase to displacement, it is as follows: (unwrapping phase * 56mm) / (- 4 * PI * cos (θ incidence)), however when applying it I obtain very large deformation value and taking into account account other data of the SGC the result values ​​do not coincide and exceed too much, do I want to know if the formula is wrong?
  3. what is the correct way to interpret the final image; that is, in what units?
    ! [image | 690x387] (upload: //wbtep1boXN3iL7MjbtNMYJkPuXI.jpeg)
    what happens is that the values ​​of vertical displacement are of more than 10 cm and that value is very high, if it is compared with those of the SGC that monitors the Volcano in real time.
    image
    image.jpg1366×768 485 KB
#298

Using the formula is the traditional way but you can as well use the “phase to displacement” module.
You have to note three things:

  • the displacement derived from the formula is a relative measure. It simply adds up the phase increase/decrease and converts it into metric units (if you enter the wavelength in mm you get the displacement in mm). You have to find a ‘zero displacement point’ in your area and calculate the remaining change from that. Explained here: Subsidence map in 3d view
  • The displacement is not in vertical direction alone but along the line of sight (LOS) between each pixel and the sensor. So you have to consider the slant looking geometry of the SAR sensor.
  • unwrapping works best if you have large connected areas of high coherence. The phase fringes are then added together to convert the circular measure to an absolute. But if, as in your case, high coherence is only available in small enclosed areas, the unrwapping/displacement values cannot be compared throughout the full image (e.g. from left to right) because the phase only gets randomly added up without being represented by the real phase information.
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#299

teniendo mi fase desenvuelta como se que lugares no has sufrido deformacion?

#300

como sé que zonas no has sufrido deformación?