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.
Why?
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.
Thanks.
best regards.
Was it after terrain correction?
Yes!
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?
@twburns
not yet, i still using my previous workout method and mostly i used the earlier date as the master and the latest as slv.
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:
i_IW1_VV_mst_02Nov2015
i_IW1_VV_slv1_09Oct2015
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.
Hi
How should the master and slave images be selected to produce the DEM? should the previous date be master or later? because the stack overview tool selects the later date as the master.
Will the results change with changing them?
As you assume no change between both images, the dates of master and slave should not matter for DEM generation.
It’s different for deformation monitoring with DInSAR where the order determines the direction of the observed movement.
More important is a large perpendicular baseline (above 100 m if possible) to enhance the patterns caused by topographic features.
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OK, thanks
But by reading different answers for this post, i still don’t know that master image should be selected before or after to deformation monitoring?!
I thought you were referring to DEM generation in your question?
Yes, my question was about the DEM and the second question was out of curiosity
Hello Dear Friends,
I have seen this discussion now and I have the similar question not answered clearly here. I have two images 2018 and 2019. If I give 2018 image as the first image in SNAP OR 2019 image first image as input, will the displacement values be the reverse values? I mean:
If 2019-2018 order for selected pixel is -30,
2018-2019 order for selected pixel will +30 , am I right?
thanks a lot
I have a little question if you wouldn’t mind, during the interferogram creation, the order of the master and slave dates determines the deformation direction relative to the satellite. Is making the older date the master image correct?
Also how can I choose which image is the master and which one is the slave through the back-geocoding Inside the graph builder? because it only seamed possible while doing back-geocoding separately
this is the standard, although both is technically possible. I’m not sure how this is solved in the Graph Builder, sorry.
No problem, I appreciate your effort. I kind of figured it out some how. The “read 2” input image in the graph builder by default is the master image. but I can never check unless I cease the graph builder and save the output before the interferogram creation step.
1 Like
good to know, thank you for sharing.
what difference does it make when the creation of interferogram assigns Master image to the one before an earthquake event for example?