Long processing time for phase unwrapping SNAPHU


I am unwrapping the phase of a product which extent is 3 bursts of a subswarth of a S1 SLC scene. I would say rather small area.

I have put SNAPHU to process it and it is now more than 12 hours without any change:

Any idea on what is happening? Is there a way to know if there is an error?

I am working on a Windows machine btw.


Have you tried running it from the command line?
Sometimes, the snaphu-unwrapping plugin in SNAP wants to copy data into a user directory which can either cause lots of unnecessary data or even prevent the tool from running, e.g. in case of insufficient writing permissions.

yes same behaviour as in the command line. I have tried subsetting the inf before unwrapping to a smaller area and I have put the number of tiles to 5 with a 200 overlap. In that way it works but would prefer to process as one single tile

What is your experience unwrapping 3 bursts of a subswath? Do you usually divide in tiles or you manage to process it at once?

Which memory settings of snap should I check in case its lacking processing resources?

Regardless of the configuration, the process should at least start. So I guess there is something more fundamental. Did you start it with administrator privilleges? Are there any special characters in the path?

So, lets try with Administrator privileges via PowerShell and with the original inf, which has not been subseted, so 3 bursts of a subswath :

  1. I run SNAPHU export again with 1 Tile, 0 Overlap (What about the tile cost threshold?)

  1. Open Windows PowerShell as Administrator

  2. cd to the snaphu folder where data has been exported

  3. run the command found in snap.conf

snaphu -f snaphu.conf Phase_ifg_IW1_VV_21Jan2015_09Jan2015.snaphu.img 20861

  1. Now I am getting an Out of memory message, which at least is something:

I guess this brings my question of how to assign more resources to SNAPHU? Or does this mean that I am forced to use Tiles in the process?

Good that you reached this stage.
Try more tiles at first.

The amount of memory that SNAPHU requires to run depends on the number of pixels in each tile. If you are trying to unwrap an interferogram without any multilooking, then you will have much larger images. If your SNAPHU program is using a large percentage of the memory on your computer, it may run very slowly even if it does not get an “out of memory” error.

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What is the effect if I have an interferogram without multi-looking then unwrapping it?. I mean after the interferogram formation, then I did S1 TOPS Deburst> Goldstein Phase Filter>Subset > Snaphu export. My unwrapping process stuck at 29 % and now more than 12 hours without any progress.

Multi-looking an interferogram prior to unwrapping not only decreases the size of the raster and therefore processing time but also reduces the chance of unwrapping errors because of its smoothing effect. There is no general advise so it depends on the quality of your interferogram if makes sense.

Thank you for your explanation. I got a new insight on this part.