Phase can only be detected between negative pi and pi; but the actual phase shift between two waves is often more than this. Phase unwrapping is the process of reconstructing the original phase shift from this "wrapped" representation. It consists of adding or subtracting multiples of 2pi in the appropriate places to make the phase image as smooth as possible.
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| Original Phase (0 to 2pi) | Unwrapped Phase (0 to 8pi) |
To convert interferometric phase into elevation, you must perform phase unwrapping.
Phase unwrapping is easy to do in areas of high coherence; but where decorrelation or layover contaminates the phase, it can be very difficult to extract topography accurately.
Often, phase unwrapping algorithms leave "holes", where they cannot determine the actual phase; or produce errors, where the unwrapped phase is inaccurate (sometimes extremely inaccurate).
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Last Updated: September 1, 1998
If you have any questions, please feel free to email olawlor@acm.org