Is there a need for a reference point? If so, how to determine the reference point?

[Xiongwei789]

Hello everyone,
I am new to using ISCE. I applied ISCE to process D-InSAR for coseismic deformation of the 2024 Neto earthquake and 2022 Chishang earthquake based on ALOS2 SCANSAR data. However, the unwrapped interferogram is strange. All the values are positive (left subplot). Is there a need for a reference point? If so, how to determine the reference point?
Thank you.

[Xiongwei789]

[david-ncu2019]

Hi,

I'm also a student in Taiwan now, I have some opinions based on my little experience with InSAR.

1/ If you would like to investigate Chishang Fault only, why don't you crop the frame that cover Taitung instead of covering the whole Taiwan map.

2/ You can try to produce the result without a reference point.

3/ In case we need reference point, we select a point far from the epicenter, for example in Yilan, or Pingtung. The stable points can be found by using GPS measurements.

[Xiongwei789]

Hi,
Thank you for your suggestions.
1/ As I'm new to using ISCE, I processed the entire map for a test. And, when I read the tutorial for processing ALOS2 data, I didn't find instructions on how to crop the frame. If you know how to do this, please let me know.
2/ Yes, I have already done that (left subplot). However, the values are negative, similar to the results for Neto earthquake test.
3/ Is there a script available in ISCE for using GPS to correct for InSAR?

[david-ncu2019]

1/ About the cropping your study area, please check this notebook: https://github.com/parosen/Geo-SInC/blob/main/EarthScope2024/1.4_Stripmap_Data_Processing_Interferometry/stripmapApp.ipynb, section crop raw data

2/ For big area, I am not sure the underlying issue, maybe you can discuss with your advisor.

3/ To correct InSAR using GPS, we need to write our own script, because the methods to do so are varied.

[Xiongwei789]

Thanks for your suggestions. I'll try them.

[ditafaith]

Hi @david-ncu2019,
Similar to @Xiongwei789 as a new user using the ISCE2 package, I am not pretty sure; suppose we want to process ALOS data; what is the difference between alos2App.py and stripmapApp.py ? Both of them for DInSAR, I guess.

[david-ncu2019]

Hi @ditafaith ,

Briefly saying, ALOS-PALSAR data has different acquisition modes (ScanSAR) and file structures, that's why ISCE provides alos2App.py

For more information, please read https://github.com/isce-framework/isce2/blob/main/contrib/stack/README.md

[ditafaith]

Please correct my understanding @david-ncu2019, thanks.
ALOS has StripMap mode that can be processed by stackStripMap.py, but alos2App.py is designated to handle all modes.

[Xiongwei789]

Hi @ditafaith ,

Briefly saying, ALOS-PALSAR data has different acquisition modes (ScanSAR) and file structures, that's why ISCE provides alos2App.py

For more information, please read https://github.com/isce-framework/isce2/blob/main/contrib/stack/README.md
Hi @david-ncu2019,
I use alos2App.py to process ScanSAR data. However, it doesn't seem to support cropping the area of interest.