ALOS2 geocode problem

[朱海雄]

I use 13 ALOS2 data to verify the baige landslide occurring in 2018 Nov  by ISCE and MintPy, 

the isce command i used was:

stackStripMap.py -s /media/leslie/F/Data/ALOS-2/SLC -d /media/leslie/F/Data/ALOS-2/DEM/demLat_N31_N32_Lon_E098_E099.dem.wgs84 -m 20171127 -W interferogram -x '31.05 31.1 98.68 98.72' -t 500 -b 200 -a 2 -r 4 -S alos -u snaphu --nofocus 

after unwarp I can invert the displacement in mintpy successfully , i open the geo_velocity.kmz in google earth  but found the outcome location seems a litttle shift:

 

Figue1 shows the LandSlide in the boundingBox

Figure 2 overlay the geo_velocity on the bounding box blue represents

the InSAR landslie by ALOS2 

there is a obvious shift between the google earth and insar outcome, i wonder why this phenomenon , i also check my other topsStack results and the location is the same with googel earth.

[Zhang Yunjun]

Hi Zhu,

You need to turn on the --zero option since ALOS-2 (stripmap I assume) SLC is focused on the zero Doppler geometry. Check the relevant discussion here: http://earthdef.caltech.edu/boards/4/topics/3737

Yunjun

[朱海雄]

thank you so much your quickly reply really help me, As your solution the --zero option shoule be set during stripstack process，and I check my TerraSAR stripmap sample，it is really right！！！

before I getting your reply i think the error maybe caused by ratio of multilook,bacause in stackStripMap.py (line 324 ) the azimuth looks will multiply by 4 if the sensor is defined as alos，I wonder why？  

     

Zhang Yunjun <yunju...@gmail.com> 于2021年4月30日周五 上午10:42写道：

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[geolee]

Hello Yunjun,

I'm processing ERS and Envisat SLC via stackStripMap.py and Mintpy as well. 

It's confusing whether I should turn on the --zero option when I'm setting stackStripMap.py parameters. 

I can barely find some information about this.

Thank you in advance.

Zhang Yunjun 在 2021年4月30日 星期五上午10:42:05 [UTC+8] 的信中寫道：

[mirzadeh...@gmail.com]

Hi Yunjun,

I processed the stack of the ALOS-1 dataset (raw format downloaded from the ASF service) using the ISCE and MintPy and observed this shift in my results between the ALOS-1 and Sentinel-1. Should I  turn on the --zero option for the ALOS-1 dataset processing? And how about --nofocus option?

-z, --zero            Use zero Doppler geometry for processing - Default : No
--nofocus             If input data is already focused to SLCs - Default : do focus

Sincerely,

Sayyed

[Zhang Yunjun]

Here (https://github.com/isce-framework/isce2/blob/c2d1a218020d81071574cd70033b7d673e2f5092/components/isceobj/StripmapProc/Factories.py#L61) is the zero Doppler SLC info in isce2. It's not easy to locate, unfortunately, someone could issue a PR for it!

For ALOS raw data, isce2 is focusing it into zero doppler by default.

Yunjun