The quality of the water level changes/ground displacement measurements with InSAR relies on the quality of the interferometric phase unwrapping product. Phase unwrapping errors are very frequent and often difficult to fix in a single interferogram.
Kepler developed a multi-frequency phase unwrapping technique that uses two phase unwrapping products from different SAR missions as long as measurements are more or less simultaneous. In this example Radarsat-2 and Cosmo-Skymed data acquired at few hours differences was used. Top and middle figures illustrate a Cosmo-Skymed, respectively a Radarsat-2 interferogram with spatial phase unwrapping errors indicated by the arrows; correct water level change measurements cannot be extracted from neither of these two products.
The bottom figure illustrates the corrected Radarsat-2 phase unwrapping product obtained from Kepler’s dual-frequency phase unwrapping technique; the phase discontinuities were eliminated and water level change can be correctly measured now.