SNAPHU Unwrapping


Appreciate the quick reply, and thank you for pointing out a much quicker way to retry the unwrapping process! I’ve tried a lot of different unwrapping parameters, but will try more.

Another thing I wanted to bring up, that I only noticed recently, is the bursts looked distorted in the S-1 TOPS Split preview only(IW 2&3 burst 9 were distorted). Just now I went back to see if other granules in the same path/frame were also like this, and they were not. Going to try using a different pair of granules for now and probably try downloading the first pair from scihub.copernicus too. (I normally get everything from ASF, being in California it’s significantly faster. ~10mins vs ~2-5hours)

Thank you again,

the previews are just a rough estimate of the single bursts. They are more or less equidistant in all SLC products but the single image’s frames can be shifted along-track between images of different acquisition dates.
Hope you manage to complete the unwrapping without errors.

I did just have to sit down and bang my head against the snaphu export parameters. Looking for any advice on attached output, curious if I can avoid some of the tiling distortions even with my limited hardware.

Hope it’s alright to share kmz’s:

Thank you again for your help.

they look quite strange (but nice result overall!)
What did you select for

  • statistical cost mode
  • initial method
  • number of tile rows / columns
  • row / column overlap
  • tile cost threshold


Statistical cost mode: DEFO
Initial method: MCF
Tile rows / columns: 80/80
Row / column overlap: 0/0
Cost threshold: 500

I would recommend to reduce the number of tiles to 12/12 and increase the overlap to at least 100. More is advised but it depends on the size of the single tiles (total number of rows divided by the number of tiles) how large you can make the overlap variable. If your tiles are only 50x50 pixels, the overlap cannot be larger and should be in relation to the total size.

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I would like to see the coherence estimation carried through snaphu unwrapping to the terrain corrected product in SNAP. The coherence image is a useful supplement to the deformation map in assessing data quality and emphasizing discontinuities in the data (faults in the case of seismic deformation.

Did the direction of interferomic displacement reverse between Snap versions 6 and 7? What was up in 6 is now down in 7? Other than installing 7, I had changed coherence window in interferogram formation from 20/10 to 10/3

Maybe has to do with this issue ?

Does the processing sequence for radar interfermetry change between v6 and 7? Around the deramp and demod processes?

In v6 I was using the menu steps. In v7 I changed to the Graph Process Tool. Maybe there are difference in default parameters between GPT and the menu steps?

Hi, I had have problems for download the images that are of the last year. I Don’t know what is the reason. but I want know how Ican download it now?.

Please use the search function of this forum. This has been answered here:

ESA Copernicus data access - Long Term Archive and its drawbacks

qglaude explains why this is the case and how you get the products. There are also some alternatives discussed in the topic.


I am having some trouble with unwrapped interferogram (Please see the image).

First interferogram is between July 1 and July 13. Second interferogram is between July 13 and july 25, and third is between July 25 and August 6. First and third interferograms look fine, however, second interferogram has a big line that does not make sense to me. Since more than one interferograms are made from same date, I think the image does not have any problem. So, what do you think the cause of error? Is it unwrapping problem, memory error or something different? Can you please suggest the remedy? Thank you for help!

it is probably related to the tiling of snaphu.
Please make sure you add some overlap between the different tiles in the snaphu.conf file
Some comments on this (and a suitable tile size) are given here: SNAPHU parameters

Hello again!

Thank you for help. However, I am still getting the line, plus the image has become even worse. Previous image was better than this. I think this is the problem related to deburst process, since all the lines are seen at perfect definite intervals (Please see image). This happened after I gave tile overlap of 200 pixels. Anything else that I can try?

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I think we see two different problems. The ones perpendicular to the image border are caused by tiling and unwrapping faults. The black ones seem to have a different reason. Are they still present if you zoom in?

At which step did you geocode your image?


This is the detailed process I did to get the unwrapped interferogram.

  1. Used Graph Builder - InSAR Graphs - TOPSAR coreg interferogram - Back Geocoding is done after applying the orbit files. I did not do any other geocoding. (Image of the graph attached)
  2. Topographic Phase Removal (Radar - Interferometric - Formation - Topographic Phase Removal)
  3. Goldstein Phase Filtering (Radar - Interferometric - Filtering - Goldstein Phase Filtering)
  4. snaphu export (I have graphical interface. I do not know how to use command based interface.) (Radar - Interferometric -Unwrapping - snaphu export)
  5. snaphu unwrapping (GUI) (Radar - Interferometric - Unwrapping - snaphu unwrapping) (Usually 1 sub-swath takes about 6000 to 7000 seconds)
  6. snaphu import (Radar - Interferometric - unwrapping - snaphu import)
  7. Phase to displacement (Radar - Interferometric - Products - Phase to displacement)
  8. Range-Doppler Terrain Correction.(Radar - Geometric - Terrain Correction - Range Doppler Terrain Correction) - Here I get final unwrapped and terrain corrected interferogram.

Black lines are there since the software was installed. I did not install the software, our HPC admin did. The lines are present even when I zoom in. But when I export the images to geotiff and open in Arcmap, black lines do not show up. So, I am guessing that black lines can be ignored.

I am really confused because I am using 11 images and have generated 10 pairs of interferograms. Out of these 10 pairs, 9 are fine, only 1 is giving trouble.

Thank you.for help!

yes, these are just a glitch from your graphic card.

Is it an option to re-process the one image pair which has stripes from scratch to see if they occur again? It was a temporary issue?


I processed the image on a local computer instead of HPC and now the image looks way better. The process was exactly the same. So, I dont know what is wrong. Strange thing is that when I used Linux, the image was not good and when I used Windows, the image was good. Sharing both the images. Anyway, thank you for help!

thank you for reporting the solution. Still a bit strange what caused the error in the end.

Hi again!

Sorry to disturb you again, but I am having another problem. I need IW2 and IW3 for my research. I am unable to produce a single image because snaphu is unable to unwrap the big image (I tried everything in my capacity as per your first commend on my first message). So, I split the image and then processed IW2 and IW3 separately. However, when I merged them, the result is unsatisfactory. When I mosaic them, I can still see a line going through the mosaic boundary. Can you please tell me what is wrong with mosaicing? (Attaching mosaiced image.)

Thank you for help!

do you get an error message?
If you define the number of tiles in a way that the size of a single tile does not exceed 3000 pixels (rows and lines), it should proceed.
If you create small subsets of your entire image before unwrapping you will inevitably get jumps at the borders after merging/mosaicing. So I would try to unwrap the entire image as one raster.
Is it an option to multi-look to a lower resolution? As you are looking at a quite large region, the initial resolution of 5x20 (or 10x10) meters might no longer be ultimately necessary.


I am unable to find a way to decrease the tile size. I don’t know where that can be changed in snaphu export. (Attached is the snapshot of snaphu export GUI) Can you please tell me how to reduce the tile size? Also, I have started the unwrapping using ‘Multilooking’. I will let you know the result.

Thank you!