PALSAR 2 Interferometry in SNAP

Microwave Toolbox Interferometry
#1

Hello,

I am learning to use PALSAR 2 imagery, and I have downloaded the two sample 1.1 images for interferometry from https://www.eorc.jaxa.jp/ALOS-2/en/doc/sam_index.htm
I used SNAP and some suggested workflows to co-register the images and then create an interferogram.
For co-registration I set up the task as shown in the images:
try1_1 try1_2
While my interferogram “looks” about normal, there are odd artifacts in the coherence product and I worry they may be altering the phase product somehow I don’t understand.

oddCoh
oddCoh523×783 157 KB

Any ideas?

#2

how does the coregistered stack look like? You can create an RGB image and check if these patterns are already contained here.

#3

So I tried it again using the Bicubic Resampling and got a slightly less-weird coherence.

odd coh2
odd coh2457×787 127 KB

I was feeling lucky and after a bit of tinkering, I managed to run it through SNAPHU and get a displacement product.
Here is the interferogram, it looks pretty good honestly.
ifg
ifg415×727 107 KB

And here is the resultant displacement image.
displ
displ371×660 43.1 KB

I am not sure how to view a coregistered stack as a RGB image, but I will attempt that next.

#4

OK, I figured out how to visualize the stack.

Here is the master and slave images as Red and Green

mstslv
mstslv921×781 222 KB

#5

the lines in azimuth direction are quite suspicious, and I think they were introduced during the coregistration.

Maybe you can select a higher polynomial in the Warp tab (Truncated synic) and compare

These lines are propagated into the interferogram (which looks nice), so I would invest a bit more time in their removal.

#7

I’ve tried several different variations in the Create Stack tool. So far, the results all look pretty similar. I have also tried the suggested higher polynomial which did not seem to alter the results much.

#8

Reminds me a bit of this case: Interferogram from Alos palsar 1.1 data

#9

I tried co registering again, and under the warp tab, used the Bicubic Interpolation method, and then got a proper coherence image.

coh fixed
coh fixed407×724 99.1 KB

#10

this looks great. Is the interferogram also correct?

#11

Yeah, it looks good as well. See below.

finalifg
finalifg407×726 95.7 KB

I intend to document the steps I took so others can hopefully make use of my mistakes.

1 Like
#12

nice! Please do so :+1:

#13

I am using the following steps:

  1. Coregistration (in the warp tab, I use the bicubic interpolation method)
  2. Interferogram Creation (I also check the box for removing the topographic phase and include coherence estimation in this step, I see some people advise this as a separate step)
  3. Goldstein Phase filtering
  4. SNAPHU export
  5. SNAPHU Phase unwrapping (so far I have had success using only the DEFO method)
  6. SNAPHU import.
  7. Phase to displacement
  8. Range Doppler Terrain Correction
#14

Hey i have been following these above mentioned steps for interferometry but I m getting error at snaphu export.I’m using ALOS 2 PALSAR2 data in snap 7.0.
Thank you

#15

Please describe your error.

#16

Hello sir, I have been trying for interferometry in snap software. As the steps mentioned above by the ballistic I have followed them. but I am getting an error when I perform phase unwrapping. The steps were coregistration, interferogram creation, phase filtering, and SNAPHU export. After this export, there were coherence and phase images, which were not opening in snap software. I am not sure where I have done the mistake. and the screenshots of the results ha been attached.
Thank youphtos.docx (3.9 MB)

#17

as you are using a quad-pol product, i recommend to use the “select band” operator at the beginning and perform the workflow on HH first to test if everything works alright. The images you currently show include all polarizations, which does not make much sense at the beginning. Please check how phase quality can differ for the polarimetric bands: Effect of polarization on interferometric products

The SNAP workflow for polarimetry you described is working with single polarization images, so I recommend to repeat it with only one polarization at a time. Then your interferograms should look more typical (currently, you are displaying an RGB image of several bands).
Maybe also this tutorial helps you: Interferometry Tutorial with Radarsat-2 It was based on Radarsat-2 images, but the steps are the same for ALOS-2.

#18

Thank you so much sir, I will surely try and attach the results as soon as I complete.

#19

That is my mistake. I was working only with the HH band in my workflow. I will update my post.

#20

I should be clear, I am working with only the HH band, the images I used were quad pol. I used the band subset to choose just the HH information

1 Like
#21

Hello Sir, I have been trying interferometry by using only one polarisation. I got stuck at the SNAPHU export step. When I export the image file of the unwrapped phase is missing. I am not getting what will be the reason for this. I have attached the screenshots of the processing steps. please provide me the solution for this error. Thank you.images interferometry.pdf (518.7 KB)