Re-calculate Interferometric Phase

I got through Sentinel-1 TOPS and subsequent operations on the way to interferometric displacement, but choked at the Band Maths Expression in the Re-calculate Interferometric Phase step.

I tried atan2(q_ifg_VV_01Jul2017_07Jul2017,i_ifg_VV_01Jul2017_07Jul2017) from the
tutorial, changing the date strings to those of my Sentinel 1 images, but the process failed. Tried date strings in various formats. Any ideas? Thanks


Edit: Sorry, this is the single image’s phase, not the interferometric phase.

atan2(q***,i***) should work. What do you mean by “the process failed”. Can you be more specific?

Thanks for reply, I tried dates in various formats, the string I used is from the pdf cookbook, so the question is how to configure the expression for my data?

I ran various versions of the expression, changing the date format, the error message was something about the 01Jul2017_07Jul2017 string not recognized.

Is the date string critical to the process or just a name?

Thanks for replying!

I’ll try replacing ‘atan2’ with ‘phase’, but I think the hang was in the date string portion of the expression.

I admit to using “cookbook” tutorials, I set out to map ground displacement at Anak Krakatau volcano. I learning at a high rate! Many thanks for help.

yes, it has to match your data. You can build it in the band maths with your i and q bands when you select “Edit Expression”

I’m a bit puzzled. Can’t you just have access to your band names ? Like in my figure below

If the Expression Editor brings the correct string from the input file, I think the problem is solved and thank you very much! I just have to build the correct expression and have a template for what it should look like.

If the string comes from the original S1 data package, I missed it, I had dumped the original data to conserve memory. If the string is not in the process input file, I can get it from the original data package. That helps a lot, thank you v much. I have some work to do. InSAR in the hands of an old geologist is v, v cool!

Solved, the Re-calculate Interferometric Phase process works by constructing the mathematical expression as follows:

In the expression editor, I type atan2(
then click the [q_ifg_VV_ …] expression in the Data Sources list
then type the comma [ , ]
then click the [i_ifg_VV_ …] expression in the Data Sources list
then typed the close parenthesis [ ) ]
the expression atan2(q_ifg_VV_ …,i_ifg_VV_ …) is good, click OK.

However, we need to confirm the order of the data sources, the resulting images are different (inverse color pallet), depending on the order in the expression. q… first, then i… Correct?

The resulting image, found in the Bands subdirectory of the last product generated in Product Explorer, is a gray scale image. This is Coherence? I expected a color fringe Radiance image. The cookbook guide to processing is sketchy here.

What/where is the best guide to S1 interferometric processing with SNAP 6.0?

Someone correct me if I’m wrong but using band maths, the results will always be in gray scale. You can manually change that in the color manipulation window.

For the “best” quide to S1, I think that there are already plenty of S1 tutorials here. I can also recommend the official ESA tutorials :

Thanks, Quentin, it was band math in the Re-calculate Interferometric Phase that made the gray scale image.

Maybe the best InSAR displacement guide is

? A RUS webinar, 2017. In that guide, there is no Re-calculate Interferometric Phase step. At the tutorial link you suggested, it seems the S1 tutorial are a few years old, difficult to follow in latest S1TBX?

I’ve been through the process, including Snaphu, did not get the expected displacement result for the recent Anak Krakatau landslide, but learned a lot. Many thanks for your help, Ken

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