Error converting phase to elevation for DEM generation


you can add the elevation band to both products (right-click on the bands) and then calculate the difference. Generally, I would say that phase to elevation performs better than phase to height for DEM creating purposes.


Did you have a look at your coherence raster? Is it good?
How large is the temporal gap between your images?
Can you please send a screenshot of the DEM and the steps you performt in the corresponding order?


In my case (I’m working in an area of Indonesian rainforest) even the coregistered data is not looking good, this is due the high temporal baseline of 12 days (in case of my Sentine-1 data). My coherence is too low, by around 0,3 for the vegetated areas.

But after I realizd this issues I was trying a test data about Pico de Fogo in Cape Verde, a vulcano with no vegetation, which was used in the SNAP TOPS Interferometry Tutorial (Veci 2015). I just wanted to know, if the phase to elevation tool is working in an area without issues due to vegetation, the coherence is much better here (displayed the stack as rgb and it is looking mostly yellow, so this should be fine) but the DEM results look just as bad.

I did the following steps:
-Interferogram (incl. coherence)
—Used a subset since here to reduce processing time
-Goldstein Filter
-Snaphu exp.
-Snaphu imp.
-Phase to elevation:

by way of comparison the real srtm for the same subset:


I also tried in the alps where not much vegetation should influences the coherence but the DEM was not better.

Thank you for your kind help!


even if coherence is high, there are still error sources like atmospheric disturbances which affect phase differently than intensity and unwrapping. A quite successful example (at least at first sight) of S1 DEM processing is shown here:


Well I did the same steps, but it could be an error of the to small baseline in my case. Yesterday I repeated my processing for a TD-X/TS-X CoSSC image (so no temporal decorelation and an effective baseline of 163m) and this one is looking much better as you can see here:

Just the three artefacts are strange, I got them in my unwrapped pase the first time.
I will play around with different baselines, maybe that is helping!
Thank you for your time :slight_smile:


yes, Sentinel-1 is no competition to the quality that can be achieved with TanDEM-X data. Looks great.

To get rid of the square-ish artefacts, you can change the number of tiles in the unwrapping config-file and compare. I assume that they are related to these tiles somehow.


Thats a very good idea! :+1: Thank you, I will try definitely changing the tiles today!


Hello, I can not find " src/snaphu_io.c file" Where it can be found?


it is located in \snaphu-v1.4.2\src and usually found by the make command.


Thanks, I downloaded mint 64 and VMmare player, but there is no file “src / snaphu_io.c file”. When you download separately the archive snaphu-v1.4.2, there is “snaphu_io.c”. But how do I unwrapping the phase? Need to install snaphu-v1.4.2?


I have no experience with vmware, but here is a tutorial I made for snaphu under windows


Thanks, I’ll try to do a unwrapping the phase with cygwin


Hello, ABraun! The file that creates cygwin “SNAPHU.EXE”, is it universal for unwrapping the phase for all radar space image?


yes, worked on all sensors for me so far. Please read here:


After the unwrapping phase scan for Sentinel-1, we obtain the values of the displacements of the earth’s surface, they are measured in centimeters or meters?


Hi Anton_Gorshkov

In my experience, the values are for default in meters, but you can to convert to cm or mm!


Hi Everyone,

i am facing some problem (Java.lang.NullPointerException) while generating DEM through Interferometric->Products->Phase to Elevation even using SNAP 5.0. (latest updated) on OS windows 8.
If i go for Interferometric->Products->Phase to Height, nothing is happening.
@squeakus did you get the solution for this problem?
Error is:
org.esa.snap.core.gpf.OperatorException: java.lang.NullPointerException
at org.esa.snap.engine_utilities.gpf.OperatorUtils.catchOperatorException(
at org.esa.s1tbx.insar.gpf.PhaseToElevationOp.computeTileStack(
at org.esa.snap.core.gpf.internal.OperatorImageTileStack.computeRect(
at org.esa.snap.core.gpf.internal.OperatorImageTileStack.computeTile(
Caused: org.esa.snap.core.gpf.OperatorException: java.lang.NullPointerException
at org.esa.snap.core.gpf.internal.OperatorExecutor$GPFImagingListener.errorOccurred(
at com.bc.ceres.glevel.MultiLevelImage.getData(
at org.esa.snap.core.gpf.internal.OperatorContext.getSourceTile(
at org.esa.snap.core.gpf.internal.OperatorContext.getSourceTile(
at org.esa.snap.core.gpf.internal.OperatorImage.computeRect(
[catch] at


I have same error java.lang.nullPointerException while generating DEM from phase. Could anyone solved this error?


I use single subswath of Sentinel 1 SLC of Indian subcontinent I also java.lang.nullPointerException when I use phase to elevation or phase to height. How can I solve the problem.


I tried phase unwrapping in ubuntu 14.04 LTS . When i run the command -
snaphu -f snaphu.conf Phase_ifg_HH_23Dec20­09_26Dec2010.snaphu.img 4672,
it gives an error saying-
snaphu v1.4.2 27 parameters input from file snaphu.conf (84 lines total) only one tile–disregarding multiprocessor option Logging run-time parameters to file snaphu.log
Segmentation fault (core dumped)
Please guide me through this. I am not using cygwin terminal.