Spatial offset of coherence using PALSAR-2 and stripmapApp

Added by Lennart Kramer 4 months ago

Hi everyone:)
I have two Alos Palsar-2 SLCs and I'd like to create a coherence map. I tried using the alos2app.py, but for some reason I didn't manage to make it run. There was always a .xml-file missing. So I thought I'd give the stripmapApp a try as my data is dual-pol stripmap. I just called "stripmapApp.py --stripmapApp.xml" and everything worked just fine until I plotted the coherence in qgis. It seems like there is a constant offset of about 500m to the west (see attached image). Unfortunately I have no Idea of what the reason might be. I tried downloading a dem with dem.py, but didn't make any difference. I'd be super grateful for any pointer on some good practices on PALSAR-2 processing.

One of the SLCs looks like this:

IMG-HV-ALOS2067251007-150821-FBDR1.1__A",

the other one is from October 2015.

I'm sorry if this is a silly question, but I'm kind of new to it and not able to proceed with my own skills at the moment.
Thanks in advance for any help:)

offset.png (786.3 kB)


Replies (12)

RE: Spatial offset of coherence using PALSAR-2 and stripmapApp - Added by Piyush Agram 4 months ago

~500m offset seems suspiciously close to the default fill value for DEMs (-500m). I would check the z.rdr / hgt.rdr file in geometry to make sure that the DEM you provided covered the actual scene.

Why not let stripmapApp.py download the DEM by itself and check. It should get the correct area, without you having to provide a DEM.

RE: Spatial offset of coherence using PALSAR-2 and stripmapApp - Added by Eric Fielding 4 months ago

Were you using the old separate `alos2app.py` or the new integrated `alos2App.py` included with ISCE2 v2.3.3? The new `alos2App.py` has new input files with examples in `examples/input_files/alos2/alos2App.xml`. The new alos2App also can automatically download the DEM.

RE: Spatial offset of coherence using PALSAR-2 and stripmapApp - Added by Lennart Kramer 4 months ago

Thank you so much Piyush and Eric for looking after this! I actually did let stripmapApp do the download in first place and just when I saw that it had this offset I tried to download in manually. Now when I look into the geometry-directory, I'm not a hundred percent sure for what I'm looking. By what I know for each pixel there are lat lon and los information. But for the "z.rdr"-file I can just find the full-resolution one. And this is not georeferenced is it?

Thanks for asking Eric. I wasn't even aware that there are two versions that are spelled almost the same. After checking, I'm using the ISCE 2.3 and the new alos2App. I oriented myself at the input in the example folder and did almost everything the same, but it always fails with the message:

"FileNotFoundError: [Errno 2] No such file or directory: '150821.track.xml'"

Although this file is produced and present in the directory from where I initiated alos2App.py.

Sorry again for the naive questions. Maybe you have another idea on what I'm doing wrong

alos2App.xml Magnifier (17.8 kB)

RE: Spatial offset of coherence using PALSAR-2 and stripmapApp - Added by Cunren Liang 4 months ago

Which version are you using? Latest code is here: https://github.com/isce-framework/isce2
Version v2.3.3 is here: https://github.com/isce-framework/isce2/releases.

Can you post all the output message from alos2App.py?

Cunren

RE: Spatial offset of coherence using PALSAR-2 and stripmapApp - Added by Lennart Kramer 4 months ago

Hi Cunren,

thank you very much for asking! I installed ISCE with conda as I'm not really familiar with scons and it intimidated me a little bit. When I run "conda list", it tells me that I have the version 2.3.3 installed.

Now when I execute alos2App.py alos2App.xml it gives me an error in the "runRdrDemOffset"-step. The complete output is attached.

thank you very much,
Robin

output.txt Magnifier (37.4 kB)

RE: Spatial offset of coherence using PALSAR-2 and stripmapApp - Added by Cunren Liang 4 months ago

This bug is already known. If you have installed the latest version, you would not have this problem. You can still use your current version, but you need to put the updated code:
https://github.com/isce-framework/isce2/blob/master/components/isceobj/Alos2Proc/runRdrDemOffset.py
in your corresponding installation directory to replace the old one.

There are other updates in the latest version, I highly recommend to use the latest version. but if you just want to compute coherence, I think that is OK.

Cunren

RE: Spatial offset of coherence using PALSAR-2 and stripmapApp - Added by Cunren Liang 4 months ago

Here is your installation dir:
/home/robin/miniconda3/envs/isce2/lib/python3.8/site-packages/isce/components/isceobj/Alos2Proc

In addition, I noticed that your images do not cover a lot of land. In this case, it's not good to do ionospheric correction. You may want to turn the following two options off:

<!--=========================================================================================
These parameters are for ionospheric corrections
==========================================================================================-->
<!--<property name="do ionospheric phase estimation">True</property>-->
<!--<property name="apply ionospheric phase correction">True</property>-->

RE: Spatial offset of coherence using PALSAR-2 and stripmapApp - Added by Eric Fielding 4 months ago

I am not sure exactly how the pipeline from GitHub to conda installations works, but it may only include the tagged releases. I am not sure there is a way to add the GitHub changes after the last 2.3.3 release.

RE: Spatial offset of coherence using PALSAR-2 and stripmapApp - Added by Lennart Kramer 4 months ago

Thanks everyone for the comments! I managed to get alos2App.py running by including the changes. However, the spatial offset doesn't disappear. As this happens to me in stripmapApp.py and in alos2App.py I guess this might be something in the data that I'm using?!

Is it possible that it relates to the DEM that gets downloaded? When I open the "dem_1_arcsec"-folder and visualize the dem in qgis I get the attached image in qgis. Is this normal?
Morover I get this warning message when running alos2App.py.

"runSlcOffset.warning message = land too small for estimating slc offsets at frame 1007, swath 1, use geometric offsets"

Regarding the ionospheric correction: I think I didn't turn it on when I excuted alos2App.py.

thanks a lot,
Robin

RE: Spatial offset of coherence using PALSAR-2 and stripmapApp - Added by Cunren Liang 4 months ago

Your DEM does not seem normal to me. This is probably over ocean or somewhere else, and that's why you got the warning message in your processing and probably also the cause of the offset in your geocoded result. This area should look like the attached image.

I am not sure what might be wrong, but perhaps you can try downloading DEM and water body manually following the ALOS-2 tutorials in your own installation directory (instead of the tutorial on github since you are not using the lastest version).

dem.png (443.4 kB)

RE: Spatial offset of coherence using PALSAR-2 and stripmapApp - Added by Cunren Liang 4 months ago

Downloading SRTM DEM and water wody needs an account. You need to have an account first. See last page of this document:
https://www.unavco.org/education/professional-development/short-courses/course-materials/insar/2016-insar-isce-giant-course-materials/Installation_instructions.pdf

Probably that's the reason why you only see flat surface in your DEM. DEM was actually not downloaded and that's only geoid surface.

RE: Spatial offset of coherence using PALSAR-2 and stripmapApp - Added by Lennart Kramer 4 months ago

Hi Cunren,

great! Thank you so much for the advices!! I'll try to set up everything as you described and then I will report if it worked or not.

(1-12/12)