Choosing slave and master image for interferometry


You’ve made this subset using SNAP? Was it after terrain correction?


Good morning,
thank you for your reply.
I have followed all the steps in order to obtain the vertical displacement of a city and my problems are the following:
1 I have repeated the same operations with the same two images in order to have a feedback and understand if the procedure followed was correct but I have not obtained the same results.
Thanks to this forum I have understood that maybe the problem is that SNAPHU start his process with a different pixel every time that I use it so even if I use the same two images and the same process the results are different and certainly this is a big problem, so I would like to know how I can resolve this problem.
2 At the end of my process I have exported the subset area (obtained inserting the coordinates of the city) in google earth and the area of the city does not correspond.
I have checked more times the coordinates and are correct…why they don’t correspond?
Please help me… I’m stuck and I can not move on.
best regards.


Was it after terrain correction?


hi, i have the same problem as same as you and @mia , i followed master and slave from stack overview, so sometimes the master must be the earlier date and slave to be the latest date or it could be vice versa.
the problem is, i usually get different result like @mia . so without the other references result maybe from the other method or someone’s analysis result, i would not know what do i do is right or not.
then the question is, how to reduce this case?
i usually work twice because of i get wrong to choose master and slave.

i hope anybody can help to answer this

thank you


@cyntiamee Did you ever get a definitive answer or work out a solution to how date order of mst/slv impacts?


not yet, i still using my previous workout method and mostly i used the earlier date as the master and the latest as slv.


@Tomcater @ABraun @cyntiamee

I think I may be having the same issue with master date being AFTER slave date even though I input the master date as the first product. SHOULD the FIRST input product be the SLAVE (later date) and the SECOND input product be the MASTER (earlier date) ?

I use snappy. This is the outline of code.

products = jpy.array(‘org.esa.snap.core.datamodel.Product’, 2)
products[0] = ProductIO.readProduct(“20151009_IW1.dim”)
products[1] = ProductIO.readProduct"(20151102_IW1.dim")
result_BG = GPF.createProduct(“Back-Geocoding”, parameters, products)

This results in an a coregestered stack with bands as follows:

You can see the master became November and the slave became October.

Is this the expected behaviour? Should I be flipping the master/slave indexes in products[]?
I want to get a time series of sequential images ie. a + b, b + c, c + d, d + e.
But right now it goes B + A, C + B, D + C, E + D which doesn’t follow logically.