Phase unwrapping and low coherence

[jchaitman]

Hi, I would like to know what a faulty unwrapped phase looks like and if this can be distinguished in the coherence image before unwrapping. Below are the phase, unwrapped phase, and coherence of a volcano with surrounding forests. I am aware that dominance of low coherence can create faulty outputs, but I am not aware of what defines a dominance of low coherence, and in this case, whether the unwrapped phase provided is faulty or not.

Thanks!

[ABraun]

Can you please share an image of the interferogram before unwrapping as well?

In general, unwrapping was successful when the cyclic patterns turned into absolute values. The only patterns which are left should be those which were already visible in the interferogram and can be related to surface motion (when topographic phase was removed) or terrain (without topographic phase removal). Whenever there are large trends superimposing the unwrapped phase (e.g. ramps from left to right) chances are high that these are not actual changes but rather unwrapping errors resulting from noisy phase areas.

Examples for good results

Source: Theory and prac-ce of phase unwrapping

Source: A new method of weighted choice in InSAR Least Squares unwrapping

Source: Braun 2021 Retrieval of digital elevation models from Sentinel-1 radar data - open applications, techniques and limitations

Examples for bad results

Source: (PDF) Extracting Digital Elevation Model (DEM) from SENTINEL-1 Satellite Imagery: Case Study a Part of Cameron Highlands, Pahang, Malaysia

Souce: Displacement from Sentinel1 - #35 by chronomanz

Source: Some problems occurred interferogram formation!

Source: Problem with the final steps of interferometry

[jchaitman]

Thanks! I have attached an image of the interferogram before unwrapping below.

[ABraun]

This is not too bad, only few decorrelated areas. The shape of the fringes indicates that they could be caused by atmosphere and not by displacement. But technically unwrapping should be possible.

[jchaitman]

Thanks you!

[Johnston]

Thanks mine issue was quit different but got the solution here keep supporting.

[seenu1996]

i am unable to run the snaphu unwrapping. It is showing like
org.esa.snap.core.gpf.OperatorException: Error on transforming template for parameter 'copyFilesTemplate
at org.esa.snap.core.gpf.operators.tooladapter.ToolAdapterOp.extractParameters(ToolAdapterOp.java:486)
at org.esa.snap.core.gpf.operators.tooladapter.ToolAdapterOp.getCommandLineTokens(ToolAdapterOp.java:459)
at org.esa.snap.core.gpf.operators.tooladapter.ToolAdapterOp.execute(ToolAdapterOp.java:346)
at org.esa.snap.core.gpf.operators.tooladapter.ToolAdapterOp.initialize(ToolAdapterOp.java:213)
at org.esa.snap.core.gpf.internal.OperatorContext.initializeOperator(OperatorContext.java:528)
at org.esa.snap.core.gpf.internal.OperatorContext.getTargetProduct(OperatorContext.java:298)
at org.esa.snap.core.gpf.Operator.getTargetProduct(Operator.java:385)
at org.esa.snap.core.gpf.operators.tooladapter.ToolAdapterOp.getResult(ToolAdapterOp.java:247)
at org.esa.snap.ui.tooladapter.dialogs.ToolAdapterExecutionDialog$OperatorTask.run(ToolAdapterExecutionDialog.java:456)
at org.netbeans.modules.progress.ui.RunOffEDTImpl$3.run(RunOffEDTImpl.java:275)
at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1443)
at org.netbeans.modules.openide.util.GlobalLookup.execute(GlobalLookup.java:68)
at org.openide.util.lookup.Lookups.executeWith(Lookups.java:303)
[catch] at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2058)
How can I solve this issue?

[TamNguyen]

My intergerogram as attached file after filter. Is this still good enough for me to do the unwrapping step. I am a bit worrying that my coherence values are quite low.

[mengdahl]

Looks like you should mask out the low coherence areas. This forum has discussions on what is a good limit for acceptable coherence.