I have several S1 12 day interferograms, I have read in various literature that by averaging them together into a stack it is possible to reduce the atmospheric artifacts. I found a few posts on this forum which mention this, but as far as I could see there was not a means to implement this through SNAP. I recently discovered the “Integer Interferogram Combination” tool, which from the help documents sounds like it may help. When I try to combine two wrapped interferograms I get an error message that “two interferograms are expected” - has anyone else encountered this error? Is there another way to average several interferograms?
Using many interferograms, indeed, minimizes the atmospheric noise. You can create a stack of all of you interferograms.
For example, let’s say that you want to identify ground subsidence during the year 2017 and you managed to acquire 10 SAR images. What you can do the following:
Create interferograms for each image pair (1->2, 2->3, 3->4, 4->5, 5->6, 6->7, 7->8,8->9 and 9->10) and derive the ground subsidence for each one of them.
Also, the results should be terrain corrected
Then you can manually add them all together to get the final ground subsidence.
Hello and thank you for the response. So the “Integer Interferogram Combination” tool cannot be used to do this? And the averaging should be done on the final displacement rasters, I read in several papers that it was the unwrapped interferomgrams that were stacked, is this incorrect, or just not currently possible within SNAP?
I am not sure what integer interferogram combination tool does, I have never used it.
In terms of deriving time series analysis using a stack of interferograms, you can either create a stack of the geocoded unwrapped phase, add them all and create the final one where you can derive the ground subsidence or you can add all of your geocoded ground displacement maps to produce the final displacement map.
I do not think that there is any difference on the method you are about to use
I’m not sure how to do what you mention. I have 3 interferograms corresponding to a period of time (1-2, 2-3, 3-4). Can I combine the interferograms in a GIS software by averaging all the interferograms?
I want to determine the subsidence of the terrain but the results are different between the interferograms and it has been difficult to determine a stable zone of zero deformation to correct the interferogram to its absolute values because my study area is the dry bed of an old lake that presents annual average subsidence of 12 cm to 25 cm.
You can use SNAP to stack your three interferograms. Once stacked, export the final stack product to geotiff format.
You can import the geotiff image into QGIS and use raster calculator to average all three interferograms.
If you do not have exact coordiantes of a location in your AOI where you know that there is not chance, use the coherence map and choose pixels with the highest coherence and subtract this value from the whole subsidence map .