DEM generation

Microwave Toolbox
#43

Dear all
please help me
when i want to use DEM generation option of SNAP it gives me an error

Capture.PNG546×554 54.7 KB

what shoud i do?
and why it show me this error?

#44

I try to make a graph for my purpose
like this:

Pasted image734×930 93.4 KB

is it wrong?
is there any problem about it?
when i want to run it, it says that,

I can’t understand why?
in stitch and unwrap tabs there is nothing to set!!
and I can’t find these 2 step separatly in software!, where are they?

#45

Don’t use those unwrap and stitch. Update to the latest SNAP version and use export to SNAPHU, use SNAPHU on linux and then import it back into SNAP.

#46

thank you but once i do it , as I said before I get bad result in transform phase to height
after that I try to use DEM generation option and get this error

I don’t know what should I do!

#47

can anybody help me?
what is the reference height for computing elevation from interfrogram?
please give me answer!

#48

Might be this helpful https://www.ims.tuwien.ac.at/publications/tuw-138083.pdf

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About InSAR atmospheric effects
#49

thanks a lot:smiley:

#50

Hi everybody
do you know , what is DEM accuracy created from Sentinel-1 data in S1TBX?
or how can we calculate it?

#51

You could compare against a validated DEM of higher quality. In general repeat-pass InSAR DEMs often have quite large errors due to loss of coherence and atmospheric artifacts.

#52

thank you mengdahl
can you explain more?
how should I do exactly?
I know that In general repeat-pass InSAR DEMs often have quite large errors due to loss of coherence and atmospheric artifacts but I do it at urban area and have high coherency!
do you think it has low accuracy?

#53

High coherence does not help if you cannot unwrap the phase, so it depends on the situation.

#54

I do unwrapping step without any problem

#55

You should study assessment of DEM quality, then compare against an existing high-quality DEM and let us know how well it works. I personally would like to know the asnwer! :slight_smile:

#56

Thank you so much mengdahl!
surely I report my result
can you give me a recommendation for reading about assessment of DEM quality?

#58

Can you please send me graph builder .xml file for DEM generation.
akshaygore@live.com
Akshay Gore

#59

@FTP Can you please send me graph builder .xml file for DEM generation.
akshaygore@live.com
Akshay Gore

#60

@Sara.Aparicio
Can you please send me graph builder .xml file for DEM generation.
akshaygore@live.com
Akshay Gore

#61

instead of using graphs, try to follow these steps and check if the output of each operator matches your needs.
Just applying a graph will probably end in bad results. Futhermore, the unwrapping can not be included in a SNAP graph and has to be performed externally.

4 Likes
#62

Good advice from @ABraun.
If you still would like a graph there are some sample graph in the Graphs menu along the top of the Graph Builder.

#63

Hi all,

I have been trying to generate a DEM with two Sentinel 1A images:
S1A_IW_SLC__1SSV_20150215T095140_20150215T095208_004632_005B63_33CB
S1A_IW_SLC__1SSV_20150227T095140_20150227T095208_004807_005FA1_24DF

I made 3 tries withouth success, these are the steps:

  1. Split
  2. Apply orbit file
  3. Coregistration
  4. IFG
  5. Goldstein filter
  6. Deburst
  7. Subset
  8. Unwrap
  9. Phase to elevation
  10. TC

I changed some of the steps and applied ESD in other attempts but withouth good results. This is one of the DEMs I obtained.

dem_3.jpg1078×944 224 KB

Could someone please tell me where the mistake is?
Thanks a lot!

Ailin

1 Like