Wrapped Interferograms Enhanced by MuLSAR Method : Applications and Comparison to Other Methods
PINEL-PUYSSEGUR, Béatrice1; KARNOUKIAN, Marc1; GRANDIN, Raphaël2; LASSERRE, Cécile3; DOIN, Marie-Pierre3; QUIN, Guillaume1; LOREAUX, Philippe1

SAR interferometry (InSAR) has proven to be a powerful technique to monitor surface displacements. However, InSAR suffers from numerous noise sources: temporal and geometric decorrelation of images, atmospheric effects, orbital or Digital Elevation Model (DEM) compensation residuals. In this study, we apply a technique called MuLSAR (Multi-Link SAR) [1] to produce robust denoised wrapped phase time series from the combination of wrapped interferograms. The principle is to combine sets of interferograms to form multiple effective interferograms with the same start and end dates, and then combine these to lower the noise in the estimate of the phase change between the two dates. The result of that process is a denoised phase-only interferogram which we call a MuLSAR interferogram. It is particularly efficient in high temporal decorrelation areas. Our method has been applied to several datasets suffering from moderate to severe temporal decorrelation, especially due to vegetation. Two ENVISAT time series are dedicated to interseismic deformation: the Levantine Fault in Lebanon and the uplift of the Himalaya. Another ENVISAT time series was used to study coseismic deformation due to a couple of earthquakes in Pakistan (28-29 October 2008). The interferograms are efficiently enhanced for every time series and helps retrieving interseismic as well as coseismic deformation. At last, the method has also been applied to a TerraSAR-X time series in the French Alps. The performance of the method is demonstrated as it enhances the post-processing steps such as DEM residual compensation and unwrapping. It is finally compared to another method of wrapped time series enhancement, SqueeSAR [2], that is based on similar principles. [1] Pinel-Puysségur, B., Michel, R., and Avouac, J.-Ph., 2012, Multi-Link InSAR time series: Enhancement of a wrapped interferometric database: IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, v. 5, doi:10.1109/JSTARS.2012.2196758. [2] Ferretti, A., A. Fumagalli, F. Novali, 2011, A New Algorithm for Processing Interferometric Data-Stacks: SqueeSAR, IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, vol. 49, 9, p. 3460-3470, DOI: 10.1109/TGRS.2011.2124465 Comparison of MuLSAR and interferograms on Pakistan earthquakes. (a) Interferogram showing deformation signal due to earthquakes. (b) MuLSAR corresponding to interferogram (a). (c) Close-up view of an interferogram showing coseismic deformation signal. (d) Same close-up view as in (c) of the corresponding MuLSAR. The signal to noise ratio is clearly enhanced in the MuLSAR compared to the conventional interferograms.