Properly using Coherence images in the Time Series tool


I have a problem with the Time Series tool ; I am trying to produce graph of coherence over time, with values extracted from polygone, so as to see how it changes for different objects over a year. I did it with backscatter images and it worked :

But when I try to do it with SLC coherence products, I obtain a graph that doesn’t seem to use all the images, or the acquisitions dates that I have. Here I use 3 different images but only two points appear on the graph :

I guess it is because coherence images are from two images with different day of acquisition ? Is there a way to use properly coherence images to produce graph where each of these is represented by one point ?

Also the text file that can be extracted from the graph gives this, if it can help :


I precise that I created a stack with my coherence images (from the .dim files), because nothing appeared on the graph just with all images opened separately on SNAP (although it worked for the GRD backscatter images).

I already looked into these topics, but I didn’t found an answer :