# SNAPHU Unwrapping

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

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.

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

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.

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I understand “CONNECTED AREAS”

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

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

this image doesnt have multilook

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.

Yes, I have the images each 12 days, but my tesis duties is calculate the deformation month by month,
Can I add the interferograms later to obtain a monthly value?

you can calculate the displacement for intervals of 12 days and then summarize them for selected periods, e.g. months. If there are linear trends in displacement, these should add up.
Furthermore, you reduce the impact of atmospheric disturbances of single interferograms.

Although it is outdated regarding the used software, this tutorial provides the full workflow to work with several consecutive interferograms: https://eo-college.org/resources/insar_deformation/

Sorry, but in the link I dont know what is the tutorial

You have to register to be able to see and download the slides.

ok gracias

Mr ABraun, excuse me but i have one ask very basic, but very important.
what is the funtion of calculate the coherence?
why I have do the calculate the coherence betwen the images?

coherence gives you an idea about where in your image the phase information is reliable. It is a measure for quality and decorrelation.

I recommend the ESA InSAR principle guidelines: http://www.esa.int/About_Us/ESA_Publications/InSAR_Principles_Guidelines_for_SAR_Interferometry_Processing_and_Interpretation_br_ESA_TM-19

thank you Mr ABraun

how can I to add two phases unwraping in snap?

how Can i add two interferograms?

we discussed this here: Interferogram averaging for DEM generation

Hi Abraum
when I finish the interferogram generation and the layer of displacement I have a rating of colors and with values. I want to know what is the correct form of interpretation the values pisitive and negative. are the values positives elevation of terrain, and values negativ subsidence?