SNAPHU Unwrapping


#328

Hi,
Can I do a layer in SNAP?
I want to do a layers of points over teh phase unwraping.


#329

you can combine several rasters or rasters with imported vectors in the layer manager grafik


#330

how can I do teh process?, I dont know to do this


#331

Did you see that there are lots of tutorials on the basic handling of the software?
http://step.esa.int/main/doc/tutorials/

If these don’t help, please specify your issue.


#332

Hi, want to know if I do the doopler correction before of unwrraping phase the error decrease?


#333

not necessarily. You can multi-look your interferogram to increase the chances of a correct unwrapping.


#334

what is the best number of multilook, for have the best result?


#335

there is no general answer on this, you will have to try and see how your result looks like.


#336

Ok. but if i dont have a model or other source with the information of displacement, how I know the result tha had the less error?


#337

High coherence and clear fringes in largely connected patterns indicate good quality of the result. You can also compare interferograms of different dates to reduce the impact of atmospheric effects.


#338

Hi, my image have a lot of noise, however when I do the process “doopler” before of unwrraping the phase I have a best result


#339

because it resamples the data to a squared pixel resolution.
I still advise to first multi-look your data (optional) and to perform the Goldstein phase filtering instead of Range Doppler Terrain Correction before unwrapping.


#340

I already made two multilook but they have two different results and I do not know which one is more accurate.


#341

Use the ones that produces the best (smooth) patterns.
Goldstein filtering can significantly increase the fringe patterns and maybe make multi-looking no longer necessary. So I would try that first on the original data.


#342

I don’t understand you want to say with
“smooth”


#343

to give an example: a) is the original, b) is the filtered (=smooth) fringe pattern. For the subsequent unwrapping b) is of course the better situation, because there are more connected areas.

Source: https://livrepository.liverpool.ac.uk/3020394/1/08340806.pdf


#344

I understand “CONNECTED AREAS”


#345

unwrapping depends on clear values without noise which lead from one color into the next along the phase cycle. This figure demonstrates it a bit:

Source: http://vldb.gsi.go.jp/sokuchi/sar/mechanism/mechanism04-e.html

If your image is noisy and doesn’t have this ‘rainbow pattern’ over larger areas (as demonstrated in red), there is no chance that the unwrapped result will reflect the true topography/displacement (blue line).

This topic might help you understand it a bit better: Some explanations about concepts of fringes of interferogram and coherence


#346

my image is noisy, Can do you say to me in your opinion, what imagen is best?

this image had multilook .

this image doesnt have multilook


#347

In the noisy areas coherence is probably low. Here filtering or multi looking doesn’t change the quality much.
Do you have the chance to use a pair with shorter temporal baseline? 02-26 June is 24 days and can probably reduced to 12 days. This would potentially increase your coherence.