Long processing time with high resolution DEM

Hello body,

I have some issue about DEM in InSAR processing with SNAP. I try to process Sentinel-1 image with an area span 2 brust. When I try to apply more precise DEM (5m resolution) instead of SRTM 30m DEM, the processing time will become about 10 times longer then processing with SRTM. For a large stack with about 40 images, it will cost several mouth to finish only one step like “interferogram formation”. I would like to ask :

  1. What reason would cause such low performance?
  2. Do I have any solution with this problem?

My platform:
OS: Fedora 26 64bit
CPU: i7-6700
Disk: 6TB Intel RST RAID0 with 2 HDD

You have an extremely powerful computer, but it looks like that SNAP is the only software that has an ability to make any computer work sloooow.

  1. I would recommend to subset your area of interest as it possible. It has to be your area and no one pixel more.
  2. You could try to tune the amount of memory which SNAP may use. You can find it Options->Perfomance: VM parameters and Cache size. To be honest, it seems to me that these parameters do nothing, but I hope in your case it might help.

Thank for your reply, I have set 6 core CPU and 16GB RAM for SNAP JVM, keeping some resource for daily working. Another thing is that I have done S-1 spilt for my images into 2 brust of 1 sub-swath, I think it was subset enough.

Your resources seem pretty enough… Maybe Marpet would recommend something.


In fact, it’s possible that this process take much longer because when you work with SRTM, first, SNAP needs to download/save the DEM in: " C:\Users\your_user.snap\auxdata\dem."

Beside the recommendation of modifying the JVM parameters, one way of improving your performance is working with a SDD disk (instead of HDD, you could choice a double boot too). This could improve two or three time the processing speed.

Of course, it’s a little more expensive but an optimum solution.

Hope this helps!

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May I know what process you did?

I run “Interferogram formation” step with the option “Remove topographic phase”, and I use external DEM with 5 meter resulation. only this step have consumed two month, and does not finish now.

I ever tried before used DEM external for InSAR and DInSAR processing. DEM external could not use for “Corregistration” and “Remove topographic phase”, it just could use for “Geocoding” process.


1-As zramadhanis mentioned, external dem option does not work for coregistration.
2-The most time consuming step in Dem generation with snap is unwrapping,the Les coherence between images, the more time it will take.
3-The issue of more processing time is largely related to the software, not the hardware features of your computer.

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I think what you mentioned would not be correct,

  1. I have coregistration using external DEM successfully with “S-1 back geocoding” and two Sentinel SLC images. Of course, it takes more time than SRTM DEM as I said at first plot.
  2. Unwrapping step with SNAPHU only need output of phase and coherence, just like files generated after step “SNAPHU export”. Most important, I am not at unwrap stage, instead of “interferogram formation”.

Just like you said at 3. So my question is :
Does SNAP do recalculate DEM phase or other things every time for every interferogram??
If it does, I think maybe developers could improve performance of this part of precessing.
And if it does NOT, I would like to know why cause such low performance and can I improve it?

Try undersampling your DEM into the same pixel-size as your SAR data, this should reduce the computational burden. Using higher resolution is not really helpful.