# TopoPhaseRemoval and stack

By following this sequence of steps:

back-geocoding -> interferogram -> deburst -> topo phase removal

I got a stack of two differential interferograms.

I have noticed that both intensity bands are equal for each pixel.
Here an example:

Since intensity band, as well phase band, is a virtual band computed from i and q bands, why do they have the same values for the intensity band and different values for the phase band?
By the way that doesn’t happen if I compute each interferogram separately (by not using the stack approach).

Is it a bug or does it have an explanation?

PS: I already tried that with more images (e.g. a stack of about 45 interferograms) and all intensity bands are equal.

I have the same problem when I export time series differential interferograms into StaMPS format , if you solve this , please let me know,thanks !

the intensity in a stack after interferogram calculation is no longer the single dates’ intensity. When you open their properties you can see something like this in the pixel expression:

`i_ifg_IW3_VV_03Feb2017_23Mar2017 * i_ifg_IW3_VV_03Feb2017_23Mar2017 + q_ifg_IW3_VV_03Feb2017_23Mar2017 * q_ifg_IW3_VV_03Feb2017_23Mar2017`

A intensity measure of both dates is somehow generated. Although I’m not sure about the theory or aim behind it.

when I do PS phase analysis in StaMPS using interferograms after TopoPhaseRemoval, I found that all differential phase values are quitely close on selected PSs, and the range of deformation rate is very small, any body have idea about this ? thx!

That is due to the definition of what an interferogram is in SNAP - we use the convention of equation (27) in my thesis (page 47):

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Yes. It is the equation that we can found in the literature.

As is written in equation (27) of your thesis the amplitude becomes the product between the amplitudes of master and slave images.
Since each interferogram in the stack has a different image as slave we should get a different intensity image for each interferogram.

That happens after the interferogram computation and after the deburst but when I remove the topographic phase contribution all the intensity bands in the stack become equal to each other.
And that doesn’t happen when I compute each interferogram separately (by not using the stacking approach).

So I think that maybe the TopoPhaseRemoval operator is not working properly when a stack of interferograms is used as input.

That is possible, @lveci could you take a look?

I’ll have a look.

I have same problem.
Have you find solutions? Thanks.